diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..4f56dc1
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,22 @@
+.DS_Store
+
+.idea
+*.iml
+
+.gradle
+
+# Ignore Gradle GUI config
+gradle-app.setting
+
+# Avoid ignoring Gradle wrapper jar file (.jar files are usually ignored)
+!gradle-wrapper.jar
+
+# Cache of project
+.gradletasknamecache
+
+build
+out
+bin
+.settings
+.classpath
+.project
\ No newline at end of file
diff --git a/Chapter_04/aop-aspectj/build.gradle b/Chapter_04/aop-aspectj/build.gradle
new file mode 100644
index 0000000..4441039
--- /dev/null
+++ b/Chapter_04/aop-aspectj/build.gradle
@@ -0,0 +1,20 @@
+plugins {
+    id 'java'
+    id "aspectj.gradle" version "0.1.6"
+    id 'application'
+}
+
+group 'com.whezh'
+version '1.0-SNAPSHOT'
+
+sourceCompatibility = 1.8
+
+repositories {
+    mavenCentral()
+}
+
+dependencies {
+    compile "org.springframework:spring-context:${springVersion}"
+}
+
+mainClassName = 'concert.Main'
diff --git a/Chapter_04/aop-aspectj/gradle.properties b/Chapter_04/aop-aspectj/gradle.properties
new file mode 100644
index 0000000..d51100e
--- /dev/null
+++ b/Chapter_04/aop-aspectj/gradle.properties
@@ -0,0 +1,3 @@
+springVersion=4.0.7.RELEASE
+systemRulesVersion=1.5.0
+aspectjVersion=1.8.5
\ No newline at end of file
diff --git a/Chapter_04/aop-aspectj/gradle/wrapper/gradle-wrapper.jar b/Chapter_04/aop-aspectj/gradle/wrapper/gradle-wrapper.jar
new file mode 100644
index 0000000..1948b90
Binary files /dev/null and b/Chapter_04/aop-aspectj/gradle/wrapper/gradle-wrapper.jar differ
diff --git a/Chapter_04/aop-aspectj/gradle/wrapper/gradle-wrapper.properties b/Chapter_04/aop-aspectj/gradle/wrapper/gradle-wrapper.properties
new file mode 100644
index 0000000..d2c45a4
--- /dev/null
+++ b/Chapter_04/aop-aspectj/gradle/wrapper/gradle-wrapper.properties
@@ -0,0 +1,5 @@
+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-4.8-bin.zip
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists
diff --git a/Chapter_04/aop-aspectj/gradlew b/Chapter_04/aop-aspectj/gradlew
new file mode 100755
index 0000000..cccdd3d
--- /dev/null
+++ b/Chapter_04/aop-aspectj/gradlew
@@ -0,0 +1,172 @@
+#!/usr/bin/env sh
+
+##############################################################################
+##
+##  Gradle start up script for UN*X
+##
+##############################################################################
+
+# Attempt to set APP_HOME
+# Resolve links: $0 may be a link
+PRG="$0"
+# Need this for relative symlinks.
+while [ -h "$PRG" ] ; do
+    ls=`ls -ld "$PRG"`
+    link=`expr "$ls" : '.*-> \(.*\)$'`
+    if expr "$link" : '/.*' > /dev/null; then
+        PRG="$link"
+    else
+        PRG=`dirname "$PRG"`"/$link"
+    fi
+done
+SAVED="`pwd`"
+cd "`dirname \"$PRG\"`/" >/dev/null
+APP_HOME="`pwd -P`"
+cd "$SAVED" >/dev/null
+
+APP_NAME="Gradle"
+APP_BASE_NAME=`basename "$0"`
+
+# Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+DEFAULT_JVM_OPTS=""
+
+# Use the maximum available, or set MAX_FD != -1 to use that value.
+MAX_FD="maximum"
+
+warn () {
+    echo "$*"
+}
+
+die () {
+    echo
+    echo "$*"
+    echo
+    exit 1
+}
+
+# OS specific support (must be 'true' or 'false').
+cygwin=false
+msys=false
+darwin=false
+nonstop=false
+case "`uname`" in
+  CYGWIN* )
+    cygwin=true
+    ;;
+  Darwin* )
+    darwin=true
+    ;;
+  MINGW* )
+    msys=true
+    ;;
+  NONSTOP* )
+    nonstop=true
+    ;;
+esac
+
+CLASSPATH=$APP_HOME/gradle/wrapper/gradle-wrapper.jar
+
+# Determine the Java command to use to start the JVM.
+if [ -n "$JAVA_HOME" ] ; then
+    if [ -x "$JAVA_HOME/jre/sh/java" ] ; then
+        # IBM's JDK on AIX uses strange locations for the executables
+        JAVACMD="$JAVA_HOME/jre/sh/java"
+    else
+        JAVACMD="$JAVA_HOME/bin/java"
+    fi
+    if [ ! -x "$JAVACMD" ] ; then
+        die "ERROR: JAVA_HOME is set to an invalid directory: $JAVA_HOME
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+    fi
+else
+    JAVACMD="java"
+    which java >/dev/null 2>&1 || die "ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+fi
+
+# Increase the maximum file descriptors if we can.
+if [ "$cygwin" = "false" -a "$darwin" = "false" -a "$nonstop" = "false" ] ; then
+    MAX_FD_LIMIT=`ulimit -H -n`
+    if [ $? -eq 0 ] ; then
+        if [ "$MAX_FD" = "maximum" -o "$MAX_FD" = "max" ] ; then
+            MAX_FD="$MAX_FD_LIMIT"
+        fi
+        ulimit -n $MAX_FD
+        if [ $? -ne 0 ] ; then
+            warn "Could not set maximum file descriptor limit: $MAX_FD"
+        fi
+    else
+        warn "Could not query maximum file descriptor limit: $MAX_FD_LIMIT"
+    fi
+fi
+
+# For Darwin, add options to specify how the application appears in the dock
+if $darwin; then
+    GRADLE_OPTS="$GRADLE_OPTS \"-Xdock:name=$APP_NAME\" \"-Xdock:icon=$APP_HOME/media/gradle.icns\""
+fi
+
+# For Cygwin, switch paths to Windows format before running java
+if $cygwin ; then
+    APP_HOME=`cygpath --path --mixed "$APP_HOME"`
+    CLASSPATH=`cygpath --path --mixed "$CLASSPATH"`
+    JAVACMD=`cygpath --unix "$JAVACMD"`
+
+    # We build the pattern for arguments to be converted via cygpath
+    ROOTDIRSRAW=`find -L / -maxdepth 1 -mindepth 1 -type d 2>/dev/null`
+    SEP=""
+    for dir in $ROOTDIRSRAW ; do
+        ROOTDIRS="$ROOTDIRS$SEP$dir"
+        SEP="|"
+    done
+    OURCYGPATTERN="(^($ROOTDIRS))"
+    # Add a user-defined pattern to the cygpath arguments
+    if [ "$GRADLE_CYGPATTERN" != "" ] ; then
+        OURCYGPATTERN="$OURCYGPATTERN|($GRADLE_CYGPATTERN)"
+    fi
+    # Now convert the arguments - kludge to limit ourselves to /bin/sh
+    i=0
+    for arg in "$@" ; do
+        CHECK=`echo "$arg"|egrep -c "$OURCYGPATTERN" -`
+        CHECK2=`echo "$arg"|egrep -c "^-"`                                 ### Determine if an option
+
+        if [ $CHECK -ne 0 ] && [ $CHECK2 -eq 0 ] ; then                    ### Added a condition
+            eval `echo args$i`=`cygpath --path --ignore --mixed "$arg"`
+        else
+            eval `echo args$i`="\"$arg\""
+        fi
+        i=$((i+1))
+    done
+    case $i in
+        (0) set -- ;;
+        (1) set -- "$args0" ;;
+        (2) set -- "$args0" "$args1" ;;
+        (3) set -- "$args0" "$args1" "$args2" ;;
+        (4) set -- "$args0" "$args1" "$args2" "$args3" ;;
+        (5) set -- "$args0" "$args1" "$args2" "$args3" "$args4" ;;
+        (6) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" ;;
+        (7) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" ;;
+        (8) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" "$args7" ;;
+        (9) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" "$args7" "$args8" ;;
+    esac
+fi
+
+# Escape application args
+save () {
+    for i do printf %s\\n "$i" | sed "s/'/'\\\\''/g;1s/^/'/;\$s/\$/' \\\\/" ; done
+    echo " "
+}
+APP_ARGS=$(save "$@")
+
+# Collect all arguments for the java command, following the shell quoting and substitution rules
+eval set -- $DEFAULT_JVM_OPTS $JAVA_OPTS $GRADLE_OPTS "\"-Dorg.gradle.appname=$APP_BASE_NAME\"" -classpath "\"$CLASSPATH\"" org.gradle.wrapper.GradleWrapperMain "$APP_ARGS"
+
+# by default we should be in the correct project dir, but when run from Finder on Mac, the cwd is wrong
+if [ "$(uname)" = "Darwin" ] && [ "$HOME" = "$PWD" ]; then
+  cd "$(dirname "$0")"
+fi
+
+exec "$JAVACMD" "$@"
diff --git a/Chapter_04/aop-aspectj/gradlew.bat b/Chapter_04/aop-aspectj/gradlew.bat
new file mode 100644
index 0000000..f955316
--- /dev/null
+++ b/Chapter_04/aop-aspectj/gradlew.bat
@@ -0,0 +1,84 @@
+@if "%DEBUG%" == "" @echo off
+@rem ##########################################################################
+@rem
+@rem  Gradle startup script for Windows
+@rem
+@rem ##########################################################################
+
+@rem Set local scope for the variables with windows NT shell
+if "%OS%"=="Windows_NT" setlocal
+
+set DIRNAME=%~dp0
+if "%DIRNAME%" == "" set DIRNAME=.
+set APP_BASE_NAME=%~n0
+set APP_HOME=%DIRNAME%
+
+@rem Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+set DEFAULT_JVM_OPTS=
+
+@rem Find java.exe
+if defined JAVA_HOME goto findJavaFromJavaHome
+
+set JAVA_EXE=java.exe
+%JAVA_EXE% -version >NUL 2>&1
+if "%ERRORLEVEL%" == "0" goto init
+
+echo.
+echo ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+echo.
+echo Please set the JAVA_HOME variable in your environment to match the
+echo location of your Java installation.
+
+goto fail
+
+:findJavaFromJavaHome
+set JAVA_HOME=%JAVA_HOME:"=%
+set JAVA_EXE=%JAVA_HOME%/bin/java.exe
+
+if exist "%JAVA_EXE%" goto init
+
+echo.
+echo ERROR: JAVA_HOME is set to an invalid directory: %JAVA_HOME%
+echo.
+echo Please set the JAVA_HOME variable in your environment to match the
+echo location of your Java installation.
+
+goto fail
+
+:init
+@rem Get command-line arguments, handling Windows variants
+
+if not "%OS%" == "Windows_NT" goto win9xME_args
+
+:win9xME_args
+@rem Slurp the command line arguments.
+set CMD_LINE_ARGS=
+set _SKIP=2
+
+:win9xME_args_slurp
+if "x%~1" == "x" goto execute
+
+set CMD_LINE_ARGS=%*
+
+:execute
+@rem Setup the command line
+
+set CLASSPATH=%APP_HOME%\gradle\wrapper\gradle-wrapper.jar
+
+@rem Execute Gradle
+"%JAVA_EXE%" %DEFAULT_JVM_OPTS% %JAVA_OPTS% %GRADLE_OPTS% "-Dorg.gradle.appname=%APP_BASE_NAME%" -classpath "%CLASSPATH%" org.gradle.wrapper.GradleWrapperMain %CMD_LINE_ARGS%
+
+:end
+@rem End local scope for the variables with windows NT shell
+if "%ERRORLEVEL%"=="0" goto mainEnd
+
+:fail
+rem Set variable GRADLE_EXIT_CONSOLE if you need the _script_ return code instead of
+rem the _cmd.exe /c_ return code!
+if  not "" == "%GRADLE_EXIT_CONSOLE%" exit 1
+exit /b 1
+
+:mainEnd
+if "%OS%"=="Windows_NT" endlocal
+
+:omega
diff --git a/Chapter_04/aop-aspectj/settings.gradle b/Chapter_04/aop-aspectj/settings.gradle
new file mode 100644
index 0000000..683c3ed
--- /dev/null
+++ b/Chapter_04/aop-aspectj/settings.gradle
@@ -0,0 +1,2 @@
+rootProject.name = 'aop'
+
diff --git a/Chapter_04/aop-aspectj/src/main/java/concert/CriticAspect.aj b/Chapter_04/aop-aspectj/src/main/java/concert/CriticAspect.aj
new file mode 100644
index 0000000..c51ce23
--- /dev/null
+++ b/Chapter_04/aop-aspectj/src/main/java/concert/CriticAspect.aj
@@ -0,0 +1,30 @@
+package concert;
+
+public aspect CriticAspect {
+    private CriticismEngine criticismEngine;
+
+    pointcut performance():execution(* concert.Performance.perform(..));
+
+    pointcut construct():execution(concert.CriticismEngineImpl.new());
+
+    after():performance(){
+        System.out.println(criticismEngine.getCriticism());
+    }
+
+    after():construct(){
+        System.out.println("After Performance constructor");
+    }
+
+
+    before():construct(){
+        System.out.println("Before Performance constructor");
+    }
+
+    public CriticismEngine getCriticismEngine() {
+        return this.criticismEngine;
+    }
+
+    public void setCriticismEngine(CriticismEngine criticismEngine) {
+        this.criticismEngine = criticismEngine;
+    }
+}
diff --git a/Chapter_04/aop-aspectj/src/main/java/concert/CriticismEngine.java b/Chapter_04/aop-aspectj/src/main/java/concert/CriticismEngine.java
new file mode 100644
index 0000000..00ddc68
--- /dev/null
+++ b/Chapter_04/aop-aspectj/src/main/java/concert/CriticismEngine.java
@@ -0,0 +1,5 @@
+package concert;
+
+public interface CriticismEngine {
+    String getCriticism();
+}
diff --git a/Chapter_04/aop-aspectj/src/main/java/concert/CriticismEngineImpl.java b/Chapter_04/aop-aspectj/src/main/java/concert/CriticismEngineImpl.java
new file mode 100644
index 0000000..39ee348
--- /dev/null
+++ b/Chapter_04/aop-aspectj/src/main/java/concert/CriticismEngineImpl.java
@@ -0,0 +1,18 @@
+package concert;
+
+public class CriticismEngineImpl implements CriticismEngine {
+    private String[] criticismPool;
+
+    public CriticismEngineImpl() {
+    }
+
+    @Override
+    public String getCriticism() {
+        int i = (int) (Math.random() * criticismPool.length);
+        return criticismPool[i];
+    }
+
+    public void setCriticismPool(String[] criticismPool) {
+        this.criticismPool = criticismPool;
+    }
+}
diff --git a/Chapter_04/aop-aspectj/src/main/java/concert/Main.java b/Chapter_04/aop-aspectj/src/main/java/concert/Main.java
new file mode 100644
index 0000000..4368b78
--- /dev/null
+++ b/Chapter_04/aop-aspectj/src/main/java/concert/Main.java
@@ -0,0 +1,13 @@
+package concert;
+
+import org.springframework.context.support.ClassPathXmlApplicationContext;
+
+public class Main {
+    public static void main(String[] args) {
+        ClassPathXmlApplicationContext context =
+                new ClassPathXmlApplicationContext("concert.xml");
+        Performance performance = context.getBean(Performance.class);
+        performance.perform();
+        context.close();
+    }
+}
diff --git a/Chapter_04/aop-aspectj/src/main/java/concert/Music.java b/Chapter_04/aop-aspectj/src/main/java/concert/Music.java
new file mode 100644
index 0000000..c1450bd
--- /dev/null
+++ b/Chapter_04/aop-aspectj/src/main/java/concert/Music.java
@@ -0,0 +1,11 @@
+package concert;
+
+import org.springframework.stereotype.Component;
+
+@Component
+public class Music implements Performance {
+    @Override
+    public void perform() {
+        System.out.println("Piano Solo");
+    }
+}
diff --git a/Chapter_04/aop-aspectj/src/main/java/concert/Performance.java b/Chapter_04/aop-aspectj/src/main/java/concert/Performance.java
new file mode 100644
index 0000000..19896c1
--- /dev/null
+++ b/Chapter_04/aop-aspectj/src/main/java/concert/Performance.java
@@ -0,0 +1,5 @@
+package concert;
+
+public interface Performance {
+    void perform();
+}
diff --git a/Chapter_04/aop-aspectj/src/main/resources/concert.xml b/Chapter_04/aop-aspectj/src/main/resources/concert.xml
new file mode 100644
index 0000000..ce98b19
--- /dev/null
+++ b/Chapter_04/aop-aspectj/src/main/resources/concert.xml
@@ -0,0 +1,21 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<beans xmlns="http://www.springframework.org/schema/beans"
+       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
+
+  <bean id="performance" class="concert.Music" />
+
+  <bean id="criticismEngine" class="concert.CriticismEngineImpl">
+    <property name="criticismPool">
+      <list>
+        <value>Worst performance ever!</value>
+        <value>I laughed, I cried, then I realized I was at the wrong show.</value>
+        <value>A must see show!</value>
+      </list>
+    </property>
+  </bean>
+
+  <bean class="concert.CriticAspect" factory-method="aspectOf">
+    <property name="criticismEngine" ref="criticismEngine" />
+  </bean>
+</beans>
\ No newline at end of file
diff --git a/Chapter_04/aop-xml/build.gradle b/Chapter_04/aop-xml/build.gradle
new file mode 100644
index 0000000..02a6131
--- /dev/null
+++ b/Chapter_04/aop-xml/build.gradle
@@ -0,0 +1,20 @@
+plugins {
+    id 'java'
+}
+
+group 'com.whezh'
+version '1.0-SNAPSHOT'
+
+sourceCompatibility = 1.8
+
+repositories {
+    mavenCentral()
+}
+
+dependencies {
+    compile "org.springframework:spring-context:${springVersion}"
+    compile("org.aspectj:aspectjweaver:${aspectjVersion}")
+
+    testCompile("org.springframework:spring-test:${springVersion}")
+    testCompile "com.github.stefanbirkner:system-rules:${systemRulesVersion}"
+}
diff --git a/Chapter_04/aop-xml/gradle.properties b/Chapter_04/aop-xml/gradle.properties
new file mode 100644
index 0000000..d9d7004
--- /dev/null
+++ b/Chapter_04/aop-xml/gradle.properties
@@ -0,0 +1,3 @@
+springVersion=4.0.7.RELEASE
+systemRulesVersion=1.5.0
+aspectjVersion=1.7.2
\ No newline at end of file
diff --git a/Chapter_04/aop-xml/gradle/wrapper/gradle-wrapper.jar b/Chapter_04/aop-xml/gradle/wrapper/gradle-wrapper.jar
new file mode 100644
index 0000000..1948b90
Binary files /dev/null and b/Chapter_04/aop-xml/gradle/wrapper/gradle-wrapper.jar differ
diff --git a/Chapter_04/aop-xml/gradle/wrapper/gradle-wrapper.properties b/Chapter_04/aop-xml/gradle/wrapper/gradle-wrapper.properties
new file mode 100644
index 0000000..d2c45a4
--- /dev/null
+++ b/Chapter_04/aop-xml/gradle/wrapper/gradle-wrapper.properties
@@ -0,0 +1,5 @@
+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-4.8-bin.zip
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists
diff --git a/Chapter_04/aop-xml/gradlew b/Chapter_04/aop-xml/gradlew
new file mode 100755
index 0000000..cccdd3d
--- /dev/null
+++ b/Chapter_04/aop-xml/gradlew
@@ -0,0 +1,172 @@
+#!/usr/bin/env sh
+
+##############################################################################
+##
+##  Gradle start up script for UN*X
+##
+##############################################################################
+
+# Attempt to set APP_HOME
+# Resolve links: $0 may be a link
+PRG="$0"
+# Need this for relative symlinks.
+while [ -h "$PRG" ] ; do
+    ls=`ls -ld "$PRG"`
+    link=`expr "$ls" : '.*-> \(.*\)$'`
+    if expr "$link" : '/.*' > /dev/null; then
+        PRG="$link"
+    else
+        PRG=`dirname "$PRG"`"/$link"
+    fi
+done
+SAVED="`pwd`"
+cd "`dirname \"$PRG\"`/" >/dev/null
+APP_HOME="`pwd -P`"
+cd "$SAVED" >/dev/null
+
+APP_NAME="Gradle"
+APP_BASE_NAME=`basename "$0"`
+
+# Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+DEFAULT_JVM_OPTS=""
+
+# Use the maximum available, or set MAX_FD != -1 to use that value.
+MAX_FD="maximum"
+
+warn () {
+    echo "$*"
+}
+
+die () {
+    echo
+    echo "$*"
+    echo
+    exit 1
+}
+
+# OS specific support (must be 'true' or 'false').
+cygwin=false
+msys=false
+darwin=false
+nonstop=false
+case "`uname`" in
+  CYGWIN* )
+    cygwin=true
+    ;;
+  Darwin* )
+    darwin=true
+    ;;
+  MINGW* )
+    msys=true
+    ;;
+  NONSTOP* )
+    nonstop=true
+    ;;
+esac
+
+CLASSPATH=$APP_HOME/gradle/wrapper/gradle-wrapper.jar
+
+# Determine the Java command to use to start the JVM.
+if [ -n "$JAVA_HOME" ] ; then
+    if [ -x "$JAVA_HOME/jre/sh/java" ] ; then
+        # IBM's JDK on AIX uses strange locations for the executables
+        JAVACMD="$JAVA_HOME/jre/sh/java"
+    else
+        JAVACMD="$JAVA_HOME/bin/java"
+    fi
+    if [ ! -x "$JAVACMD" ] ; then
+        die "ERROR: JAVA_HOME is set to an invalid directory: $JAVA_HOME
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+    fi
+else
+    JAVACMD="java"
+    which java >/dev/null 2>&1 || die "ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+fi
+
+# Increase the maximum file descriptors if we can.
+if [ "$cygwin" = "false" -a "$darwin" = "false" -a "$nonstop" = "false" ] ; then
+    MAX_FD_LIMIT=`ulimit -H -n`
+    if [ $? -eq 0 ] ; then
+        if [ "$MAX_FD" = "maximum" -o "$MAX_FD" = "max" ] ; then
+            MAX_FD="$MAX_FD_LIMIT"
+        fi
+        ulimit -n $MAX_FD
+        if [ $? -ne 0 ] ; then
+            warn "Could not set maximum file descriptor limit: $MAX_FD"
+        fi
+    else
+        warn "Could not query maximum file descriptor limit: $MAX_FD_LIMIT"
+    fi
+fi
+
+# For Darwin, add options to specify how the application appears in the dock
+if $darwin; then
+    GRADLE_OPTS="$GRADLE_OPTS \"-Xdock:name=$APP_NAME\" \"-Xdock:icon=$APP_HOME/media/gradle.icns\""
+fi
+
+# For Cygwin, switch paths to Windows format before running java
+if $cygwin ; then
+    APP_HOME=`cygpath --path --mixed "$APP_HOME"`
+    CLASSPATH=`cygpath --path --mixed "$CLASSPATH"`
+    JAVACMD=`cygpath --unix "$JAVACMD"`
+
+    # We build the pattern for arguments to be converted via cygpath
+    ROOTDIRSRAW=`find -L / -maxdepth 1 -mindepth 1 -type d 2>/dev/null`
+    SEP=""
+    for dir in $ROOTDIRSRAW ; do
+        ROOTDIRS="$ROOTDIRS$SEP$dir"
+        SEP="|"
+    done
+    OURCYGPATTERN="(^($ROOTDIRS))"
+    # Add a user-defined pattern to the cygpath arguments
+    if [ "$GRADLE_CYGPATTERN" != "" ] ; then
+        OURCYGPATTERN="$OURCYGPATTERN|($GRADLE_CYGPATTERN)"
+    fi
+    # Now convert the arguments - kludge to limit ourselves to /bin/sh
+    i=0
+    for arg in "$@" ; do
+        CHECK=`echo "$arg"|egrep -c "$OURCYGPATTERN" -`
+        CHECK2=`echo "$arg"|egrep -c "^-"`                                 ### Determine if an option
+
+        if [ $CHECK -ne 0 ] && [ $CHECK2 -eq 0 ] ; then                    ### Added a condition
+            eval `echo args$i`=`cygpath --path --ignore --mixed "$arg"`
+        else
+            eval `echo args$i`="\"$arg\""
+        fi
+        i=$((i+1))
+    done
+    case $i in
+        (0) set -- ;;
+        (1) set -- "$args0" ;;
+        (2) set -- "$args0" "$args1" ;;
+        (3) set -- "$args0" "$args1" "$args2" ;;
+        (4) set -- "$args0" "$args1" "$args2" "$args3" ;;
+        (5) set -- "$args0" "$args1" "$args2" "$args3" "$args4" ;;
+        (6) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" ;;
+        (7) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" ;;
+        (8) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" "$args7" ;;
+        (9) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" "$args7" "$args8" ;;
+    esac
+fi
+
+# Escape application args
+save () {
+    for i do printf %s\\n "$i" | sed "s/'/'\\\\''/g;1s/^/'/;\$s/\$/' \\\\/" ; done
+    echo " "
+}
+APP_ARGS=$(save "$@")
+
+# Collect all arguments for the java command, following the shell quoting and substitution rules
+eval set -- $DEFAULT_JVM_OPTS $JAVA_OPTS $GRADLE_OPTS "\"-Dorg.gradle.appname=$APP_BASE_NAME\"" -classpath "\"$CLASSPATH\"" org.gradle.wrapper.GradleWrapperMain "$APP_ARGS"
+
+# by default we should be in the correct project dir, but when run from Finder on Mac, the cwd is wrong
+if [ "$(uname)" = "Darwin" ] && [ "$HOME" = "$PWD" ]; then
+  cd "$(dirname "$0")"
+fi
+
+exec "$JAVACMD" "$@"
diff --git a/Chapter_04/aop-xml/gradlew.bat b/Chapter_04/aop-xml/gradlew.bat
new file mode 100644
index 0000000..f955316
--- /dev/null
+++ b/Chapter_04/aop-xml/gradlew.bat
@@ -0,0 +1,84 @@
+@if "%DEBUG%" == "" @echo off
+@rem ##########################################################################
+@rem
+@rem  Gradle startup script for Windows
+@rem
+@rem ##########################################################################
+
+@rem Set local scope for the variables with windows NT shell
+if "%OS%"=="Windows_NT" setlocal
+
+set DIRNAME=%~dp0
+if "%DIRNAME%" == "" set DIRNAME=.
+set APP_BASE_NAME=%~n0
+set APP_HOME=%DIRNAME%
+
+@rem Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+set DEFAULT_JVM_OPTS=
+
+@rem Find java.exe
+if defined JAVA_HOME goto findJavaFromJavaHome
+
+set JAVA_EXE=java.exe
+%JAVA_EXE% -version >NUL 2>&1
+if "%ERRORLEVEL%" == "0" goto init
+
+echo.
+echo ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+echo.
+echo Please set the JAVA_HOME variable in your environment to match the
+echo location of your Java installation.
+
+goto fail
+
+:findJavaFromJavaHome
+set JAVA_HOME=%JAVA_HOME:"=%
+set JAVA_EXE=%JAVA_HOME%/bin/java.exe
+
+if exist "%JAVA_EXE%" goto init
+
+echo.
+echo ERROR: JAVA_HOME is set to an invalid directory: %JAVA_HOME%
+echo.
+echo Please set the JAVA_HOME variable in your environment to match the
+echo location of your Java installation.
+
+goto fail
+
+:init
+@rem Get command-line arguments, handling Windows variants
+
+if not "%OS%" == "Windows_NT" goto win9xME_args
+
+:win9xME_args
+@rem Slurp the command line arguments.
+set CMD_LINE_ARGS=
+set _SKIP=2
+
+:win9xME_args_slurp
+if "x%~1" == "x" goto execute
+
+set CMD_LINE_ARGS=%*
+
+:execute
+@rem Setup the command line
+
+set CLASSPATH=%APP_HOME%\gradle\wrapper\gradle-wrapper.jar
+
+@rem Execute Gradle
+"%JAVA_EXE%" %DEFAULT_JVM_OPTS% %JAVA_OPTS% %GRADLE_OPTS% "-Dorg.gradle.appname=%APP_BASE_NAME%" -classpath "%CLASSPATH%" org.gradle.wrapper.GradleWrapperMain %CMD_LINE_ARGS%
+
+:end
+@rem End local scope for the variables with windows NT shell
+if "%ERRORLEVEL%"=="0" goto mainEnd
+
+:fail
+rem Set variable GRADLE_EXIT_CONSOLE if you need the _script_ return code instead of
+rem the _cmd.exe /c_ return code!
+if  not "" == "%GRADLE_EXIT_CONSOLE%" exit 1
+exit /b 1
+
+:mainEnd
+if "%OS%"=="Windows_NT" endlocal
+
+:omega
diff --git a/Chapter_04/aop-xml/settings.gradle b/Chapter_04/aop-xml/settings.gradle
new file mode 100644
index 0000000..683c3ed
--- /dev/null
+++ b/Chapter_04/aop-xml/settings.gradle
@@ -0,0 +1,2 @@
+rootProject.name = 'aop'
+
diff --git a/Chapter_04/aop-xml/src/main/java/concert/Audience.java b/Chapter_04/aop-xml/src/main/java/concert/Audience.java
new file mode 100644
index 0000000..3e3053e
--- /dev/null
+++ b/Chapter_04/aop-xml/src/main/java/concert/Audience.java
@@ -0,0 +1,32 @@
+package concert;
+
+import org.aspectj.lang.ProceedingJoinPoint;
+
+public class Audience {
+    public void silenceCellPhone() {
+        System.out.println("Silencing cell phones");
+    }
+
+    public void takeSeats() {
+        System.out.println("Taking seats");
+    }
+
+    public void applause() {
+        System.out.println("CLAP CLAP CLAP!!!");
+    }
+
+    public void demandRefund() {
+        System.out.println("Demanding a refund");
+    }
+
+    public void watchPerformance(ProceedingJoinPoint jp) {
+        try {
+            System.out.println("Silencing cell phones");
+            System.out.println("Taking seats");
+            jp.proceed();
+            System.out.println("CLAP CLAP CLAP!!!");
+        } catch (Throwable e) {
+            System.out.println("Demanding a refund");
+        }
+    }
+}
diff --git a/Chapter_04/aop-xml/src/main/java/concert/DefaultEncoreable.java b/Chapter_04/aop-xml/src/main/java/concert/DefaultEncoreable.java
new file mode 100644
index 0000000..d06729e
--- /dev/null
+++ b/Chapter_04/aop-xml/src/main/java/concert/DefaultEncoreable.java
@@ -0,0 +1,8 @@
+package concert;
+
+public class DefaultEncoreable implements Encoreable {
+    @Override
+    public void performEncore() {
+        System.out.println("Default encoreable");
+    }
+}
diff --git a/Chapter_04/aop-xml/src/main/java/concert/Encoreable.java b/Chapter_04/aop-xml/src/main/java/concert/Encoreable.java
new file mode 100644
index 0000000..822ad00
--- /dev/null
+++ b/Chapter_04/aop-xml/src/main/java/concert/Encoreable.java
@@ -0,0 +1,5 @@
+package concert;
+
+public interface Encoreable {
+    void performEncore();
+}
diff --git a/Chapter_04/aop-xml/src/main/java/concert/Music.java b/Chapter_04/aop-xml/src/main/java/concert/Music.java
new file mode 100644
index 0000000..719cf2c
--- /dev/null
+++ b/Chapter_04/aop-xml/src/main/java/concert/Music.java
@@ -0,0 +1,8 @@
+package concert;
+
+public class Music implements Performance {
+    @Override
+    public void perform() {
+        System.out.println("Piano Solo");
+    }
+}
diff --git a/Chapter_04/aop-xml/src/main/java/concert/Performance.java b/Chapter_04/aop-xml/src/main/java/concert/Performance.java
new file mode 100644
index 0000000..19896c1
--- /dev/null
+++ b/Chapter_04/aop-xml/src/main/java/concert/Performance.java
@@ -0,0 +1,5 @@
+package concert;
+
+public interface Performance {
+    void perform();
+}
diff --git a/Chapter_04/aop-xml/src/main/java/params/BlankDisc.java b/Chapter_04/aop-xml/src/main/java/params/BlankDisc.java
new file mode 100644
index 0000000..8cf45f9
--- /dev/null
+++ b/Chapter_04/aop-xml/src/main/java/params/BlankDisc.java
@@ -0,0 +1,33 @@
+package params;
+
+import java.util.List;
+
+public class BlankDisc implements CompactDisc {
+
+    private String title;
+    private String artist;
+    private List<String> tracks;
+
+    public void setTitle(String title) {
+        this.title = title;
+    }
+
+    public void setArtist(String artist) {
+        this.artist = artist;
+    }
+
+    public void setTracks(List<String> tracks) {
+        this.tracks = tracks;
+    }
+
+    public void play() {
+        System.out.println("Playing " + title + " by " + artist);
+        for (int i = 0; i < tracks.size(); i++) {
+            playTrack(i);
+        }
+    }
+
+    public void playTrack(int track) {
+        System.out.println("-Track: " + tracks.get(track));
+    }
+}
diff --git a/Chapter_04/aop-xml/src/main/java/params/CompactDisc.java b/Chapter_04/aop-xml/src/main/java/params/CompactDisc.java
new file mode 100644
index 0000000..8bfab5f
--- /dev/null
+++ b/Chapter_04/aop-xml/src/main/java/params/CompactDisc.java
@@ -0,0 +1,7 @@
+package params;
+
+public interface CompactDisc {
+    void play();
+
+    void playTrack(int track);
+}
diff --git a/Chapter_04/aop-xml/src/main/java/params/TrackCounter.java b/Chapter_04/aop-xml/src/main/java/params/TrackCounter.java
new file mode 100644
index 0000000..8b8628b
--- /dev/null
+++ b/Chapter_04/aop-xml/src/main/java/params/TrackCounter.java
@@ -0,0 +1,18 @@
+package params;
+
+import java.util.HashMap;
+import java.util.Map;
+
+public class TrackCounter {
+
+    private Map<Integer, Integer> trackCounts = new HashMap<>();
+
+    public void countTrack(int trackNumber) {
+        int currentCount = getPlayCount(trackNumber);
+        trackCounts.put(trackNumber, currentCount + 1);
+    }
+
+    public int getPlayCount(int trackNumber) {
+        return trackCounts.getOrDefault(trackNumber, 0);
+    }
+}
diff --git a/Chapter_04/aop-xml/src/main/resources/concert.xml b/Chapter_04/aop-xml/src/main/resources/concert.xml
new file mode 100644
index 0000000..51364c6
--- /dev/null
+++ b/Chapter_04/aop-xml/src/main/resources/concert.xml
@@ -0,0 +1,31 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<beans xmlns="http://www.springframework.org/schema/beans"
+       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+       xmlns:aop="http://www.springframework.org/schema/aop"
+       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop.xsd">
+
+  <bean id="music" class="concert.Music" />
+  <bean id="audience" class="concert.Audience" />
+
+  <aop:config>
+    <aop:aspect ref="audience">
+      <aop:pointcut id="performance" expression="execution(* concert.Performance.perform(..))" />
+
+      <!--<aop:before method="silenceCellPhone" pointcut-ref="performance" />-->
+      <!--<aop:before method="takeSeats" pointcut-ref="performance" />-->
+      <!--<aop:after-returning method="applause" pointcut-ref="performance" />-->
+      <!--<aop:after-throwing method="demandRefund" pointcut-ref="performance" />-->
+
+      <aop:around method="watchPerformance" pointcut-ref="performance" />
+
+    </aop:aspect>
+
+    <aop:aspect>
+      <aop:declare-parents
+          types-matching="concert.Performance+"
+          implement-interface="concert.Encoreable"
+          default-impl="concert.DefaultEncoreable"
+      />
+    </aop:aspect>
+  </aop:config>
+</beans>
\ No newline at end of file
diff --git a/Chapter_04/aop-xml/src/main/resources/params.xml b/Chapter_04/aop-xml/src/main/resources/params.xml
new file mode 100644
index 0000000..9777a71
--- /dev/null
+++ b/Chapter_04/aop-xml/src/main/resources/params.xml
@@ -0,0 +1,40 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<beans xmlns="http://www.springframework.org/schema/beans"
+       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+       xmlns:p="http://www.springframework.org/schema/p"
+       xmlns:aop="http://www.springframework.org/schema/aop"
+       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop.xsd">
+
+  <bean id="cd"
+        class="params.BlankDisc"
+        p:title="Sgt. Pepper's Lonely Hearts Club Band"
+        p:artist="The Beatles">
+    <property name="tracks">
+      <list>
+        <value>Sgt. Pepper's Lonely Hearts Club Band</value>
+        <value>With a Little Help from My Friends</value>
+        <value>Lucy in the Sky with Diamonds</value>
+        <value>Getting Better</value>
+        <value>Fixing a Hole</value>
+        <value>She's Leaving Home</value>
+        <value>Being for the Benefit of Mr. Kite!</value>
+        <value>Within You Without You</value>
+        <value>When I'm Sixty-Four</value>
+        <value>Lovely Rita</value>
+        <value>Good Morning Good Morning</value>
+        <value>Sgt. Pepper's Lonely Hearts Club Band (Reprise)</value>
+        <value>A Day in the Life</value>
+      </list>
+    </property>
+  </bean>
+  <bean id="trackCounter" class="params.TrackCounter" />
+
+  <aop:config>
+    <aop:aspect ref="trackCounter">
+      <aop:pointcut id="trackPlayed"
+                    expression="execution(* params.CompactDisc.playTrack(int)) and args(trackNumber)*" />
+
+      <aop:before method="countTrack" pointcut-ref="trackPlayed" />
+    </aop:aspect>
+  </aop:config>
+</beans>
\ No newline at end of file
diff --git a/Chapter_04/aop-xml/src/test/java/concert/ConcertTest.java b/Chapter_04/aop-xml/src/test/java/concert/ConcertTest.java
new file mode 100644
index 0000000..d777da1
--- /dev/null
+++ b/Chapter_04/aop-xml/src/test/java/concert/ConcertTest.java
@@ -0,0 +1,30 @@
+package concert;
+
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.test.context.ContextConfiguration;
+import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
+import org.junit.contrib.java.lang.system.StandardOutputStreamLog;
+
+import static org.junit.Assert.assertEquals;
+
+@RunWith(SpringJUnit4ClassRunner.class)
+@ContextConfiguration("classpath:concert.xml")
+public class ConcertTest {
+    @Rule
+    public final StandardOutputStreamLog log = new StandardOutputStreamLog();
+
+    @Autowired
+    private Performance performance;
+
+    @Test
+    public void testPerformance() {
+        performance.perform();
+        assertEquals("Silencing cell phones\n" +
+                "Taking seats\n" +
+                "Piano Solo\n" +
+                "CLAP CLAP CLAP!!!\n", log.getLog());
+    }
+}
diff --git a/Chapter_04/aop-xml/src/test/java/concert/EncoreableTest.java b/Chapter_04/aop-xml/src/test/java/concert/EncoreableTest.java
new file mode 100644
index 0000000..2b67902
--- /dev/null
+++ b/Chapter_04/aop-xml/src/test/java/concert/EncoreableTest.java
@@ -0,0 +1,27 @@
+package concert;
+
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.contrib.java.lang.system.StandardOutputStreamLog;
+import org.junit.runner.RunWith;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.test.context.ContextConfiguration;
+import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
+
+import static org.junit.Assert.assertEquals;
+
+@RunWith(SpringJUnit4ClassRunner.class)
+@ContextConfiguration("classpath:concert.xml")
+public class EncoreableTest {
+    @Rule
+    public final StandardOutputStreamLog log = new StandardOutputStreamLog();
+
+    @Autowired
+    private Encoreable performance;
+
+    @Test
+    public void testPerformance() {
+        performance.performEncore();
+        assertEquals("Default encoreable\n", log.getLog());
+    }
+}
diff --git a/Chapter_04/aop-xml/src/test/java/params/TrackCountTest.java b/Chapter_04/aop-xml/src/test/java/params/TrackCountTest.java
new file mode 100644
index 0000000..55fa56a
--- /dev/null
+++ b/Chapter_04/aop-xml/src/test/java/params/TrackCountTest.java
@@ -0,0 +1,40 @@
+package params;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.test.context.ContextConfiguration;
+import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
+
+import static org.junit.Assert.assertEquals;
+
+@RunWith(SpringJUnit4ClassRunner.class)
+@ContextConfiguration("classpath:params.xml")
+public class TrackCountTest {
+    @Autowired
+    private CompactDisc cd;
+
+    @Autowired
+    private TrackCounter counter;
+
+    @Test
+    public void testTrackCounter() {
+        cd.playTrack(1);
+        cd.playTrack(2);
+        cd.playTrack(3);
+        cd.playTrack(3);
+        cd.playTrack(3);
+        cd.playTrack(3);
+        cd.playTrack(6);
+        cd.playTrack(7);
+        cd.playTrack(7);
+
+        assertEquals(1, counter.getPlayCount(1));
+        assertEquals(1, counter.getPlayCount(2));
+        assertEquals(4, counter.getPlayCount(3));
+        assertEquals(0, counter.getPlayCount(4));
+        assertEquals(0, counter.getPlayCount(5));
+        assertEquals(1, counter.getPlayCount(6));
+        assertEquals(2, counter.getPlayCount(7));
+    }
+}
diff --git a/Chapter_04/aop/build.gradle b/Chapter_04/aop/build.gradle
new file mode 100644
index 0000000..02a6131
--- /dev/null
+++ b/Chapter_04/aop/build.gradle
@@ -0,0 +1,20 @@
+plugins {
+    id 'java'
+}
+
+group 'com.whezh'
+version '1.0-SNAPSHOT'
+
+sourceCompatibility = 1.8
+
+repositories {
+    mavenCentral()
+}
+
+dependencies {
+    compile "org.springframework:spring-context:${springVersion}"
+    compile("org.aspectj:aspectjweaver:${aspectjVersion}")
+
+    testCompile("org.springframework:spring-test:${springVersion}")
+    testCompile "com.github.stefanbirkner:system-rules:${systemRulesVersion}"
+}
diff --git a/Chapter_04/aop/gradle.properties b/Chapter_04/aop/gradle.properties
new file mode 100644
index 0000000..d9d7004
--- /dev/null
+++ b/Chapter_04/aop/gradle.properties
@@ -0,0 +1,3 @@
+springVersion=4.0.7.RELEASE
+systemRulesVersion=1.5.0
+aspectjVersion=1.7.2
\ No newline at end of file
diff --git a/Chapter_04/aop/gradle/wrapper/gradle-wrapper.jar b/Chapter_04/aop/gradle/wrapper/gradle-wrapper.jar
new file mode 100644
index 0000000..1948b90
Binary files /dev/null and b/Chapter_04/aop/gradle/wrapper/gradle-wrapper.jar differ
diff --git a/Chapter_04/aop/gradle/wrapper/gradle-wrapper.properties b/Chapter_04/aop/gradle/wrapper/gradle-wrapper.properties
new file mode 100644
index 0000000..d2c45a4
--- /dev/null
+++ b/Chapter_04/aop/gradle/wrapper/gradle-wrapper.properties
@@ -0,0 +1,5 @@
+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-4.8-bin.zip
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists
diff --git a/Chapter_04/aop/gradlew b/Chapter_04/aop/gradlew
new file mode 100755
index 0000000..cccdd3d
--- /dev/null
+++ b/Chapter_04/aop/gradlew
@@ -0,0 +1,172 @@
+#!/usr/bin/env sh
+
+##############################################################################
+##
+##  Gradle start up script for UN*X
+##
+##############################################################################
+
+# Attempt to set APP_HOME
+# Resolve links: $0 may be a link
+PRG="$0"
+# Need this for relative symlinks.
+while [ -h "$PRG" ] ; do
+    ls=`ls -ld "$PRG"`
+    link=`expr "$ls" : '.*-> \(.*\)$'`
+    if expr "$link" : '/.*' > /dev/null; then
+        PRG="$link"
+    else
+        PRG=`dirname "$PRG"`"/$link"
+    fi
+done
+SAVED="`pwd`"
+cd "`dirname \"$PRG\"`/" >/dev/null
+APP_HOME="`pwd -P`"
+cd "$SAVED" >/dev/null
+
+APP_NAME="Gradle"
+APP_BASE_NAME=`basename "$0"`
+
+# Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+DEFAULT_JVM_OPTS=""
+
+# Use the maximum available, or set MAX_FD != -1 to use that value.
+MAX_FD="maximum"
+
+warn () {
+    echo "$*"
+}
+
+die () {
+    echo
+    echo "$*"
+    echo
+    exit 1
+}
+
+# OS specific support (must be 'true' or 'false').
+cygwin=false
+msys=false
+darwin=false
+nonstop=false
+case "`uname`" in
+  CYGWIN* )
+    cygwin=true
+    ;;
+  Darwin* )
+    darwin=true
+    ;;
+  MINGW* )
+    msys=true
+    ;;
+  NONSTOP* )
+    nonstop=true
+    ;;
+esac
+
+CLASSPATH=$APP_HOME/gradle/wrapper/gradle-wrapper.jar
+
+# Determine the Java command to use to start the JVM.
+if [ -n "$JAVA_HOME" ] ; then
+    if [ -x "$JAVA_HOME/jre/sh/java" ] ; then
+        # IBM's JDK on AIX uses strange locations for the executables
+        JAVACMD="$JAVA_HOME/jre/sh/java"
+    else
+        JAVACMD="$JAVA_HOME/bin/java"
+    fi
+    if [ ! -x "$JAVACMD" ] ; then
+        die "ERROR: JAVA_HOME is set to an invalid directory: $JAVA_HOME
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+    fi
+else
+    JAVACMD="java"
+    which java >/dev/null 2>&1 || die "ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+fi
+
+# Increase the maximum file descriptors if we can.
+if [ "$cygwin" = "false" -a "$darwin" = "false" -a "$nonstop" = "false" ] ; then
+    MAX_FD_LIMIT=`ulimit -H -n`
+    if [ $? -eq 0 ] ; then
+        if [ "$MAX_FD" = "maximum" -o "$MAX_FD" = "max" ] ; then
+            MAX_FD="$MAX_FD_LIMIT"
+        fi
+        ulimit -n $MAX_FD
+        if [ $? -ne 0 ] ; then
+            warn "Could not set maximum file descriptor limit: $MAX_FD"
+        fi
+    else
+        warn "Could not query maximum file descriptor limit: $MAX_FD_LIMIT"
+    fi
+fi
+
+# For Darwin, add options to specify how the application appears in the dock
+if $darwin; then
+    GRADLE_OPTS="$GRADLE_OPTS \"-Xdock:name=$APP_NAME\" \"-Xdock:icon=$APP_HOME/media/gradle.icns\""
+fi
+
+# For Cygwin, switch paths to Windows format before running java
+if $cygwin ; then
+    APP_HOME=`cygpath --path --mixed "$APP_HOME"`
+    CLASSPATH=`cygpath --path --mixed "$CLASSPATH"`
+    JAVACMD=`cygpath --unix "$JAVACMD"`
+
+    # We build the pattern for arguments to be converted via cygpath
+    ROOTDIRSRAW=`find -L / -maxdepth 1 -mindepth 1 -type d 2>/dev/null`
+    SEP=""
+    for dir in $ROOTDIRSRAW ; do
+        ROOTDIRS="$ROOTDIRS$SEP$dir"
+        SEP="|"
+    done
+    OURCYGPATTERN="(^($ROOTDIRS))"
+    # Add a user-defined pattern to the cygpath arguments
+    if [ "$GRADLE_CYGPATTERN" != "" ] ; then
+        OURCYGPATTERN="$OURCYGPATTERN|($GRADLE_CYGPATTERN)"
+    fi
+    # Now convert the arguments - kludge to limit ourselves to /bin/sh
+    i=0
+    for arg in "$@" ; do
+        CHECK=`echo "$arg"|egrep -c "$OURCYGPATTERN" -`
+        CHECK2=`echo "$arg"|egrep -c "^-"`                                 ### Determine if an option
+
+        if [ $CHECK -ne 0 ] && [ $CHECK2 -eq 0 ] ; then                    ### Added a condition
+            eval `echo args$i`=`cygpath --path --ignore --mixed "$arg"`
+        else
+            eval `echo args$i`="\"$arg\""
+        fi
+        i=$((i+1))
+    done
+    case $i in
+        (0) set -- ;;
+        (1) set -- "$args0" ;;
+        (2) set -- "$args0" "$args1" ;;
+        (3) set -- "$args0" "$args1" "$args2" ;;
+        (4) set -- "$args0" "$args1" "$args2" "$args3" ;;
+        (5) set -- "$args0" "$args1" "$args2" "$args3" "$args4" ;;
+        (6) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" ;;
+        (7) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" ;;
+        (8) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" "$args7" ;;
+        (9) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" "$args7" "$args8" ;;
+    esac
+fi
+
+# Escape application args
+save () {
+    for i do printf %s\\n "$i" | sed "s/'/'\\\\''/g;1s/^/'/;\$s/\$/' \\\\/" ; done
+    echo " "
+}
+APP_ARGS=$(save "$@")
+
+# Collect all arguments for the java command, following the shell quoting and substitution rules
+eval set -- $DEFAULT_JVM_OPTS $JAVA_OPTS $GRADLE_OPTS "\"-Dorg.gradle.appname=$APP_BASE_NAME\"" -classpath "\"$CLASSPATH\"" org.gradle.wrapper.GradleWrapperMain "$APP_ARGS"
+
+# by default we should be in the correct project dir, but when run from Finder on Mac, the cwd is wrong
+if [ "$(uname)" = "Darwin" ] && [ "$HOME" = "$PWD" ]; then
+  cd "$(dirname "$0")"
+fi
+
+exec "$JAVACMD" "$@"
diff --git a/Chapter_04/aop/gradlew.bat b/Chapter_04/aop/gradlew.bat
new file mode 100644
index 0000000..f955316
--- /dev/null
+++ b/Chapter_04/aop/gradlew.bat
@@ -0,0 +1,84 @@
+@if "%DEBUG%" == "" @echo off
+@rem ##########################################################################
+@rem
+@rem  Gradle startup script for Windows
+@rem
+@rem ##########################################################################
+
+@rem Set local scope for the variables with windows NT shell
+if "%OS%"=="Windows_NT" setlocal
+
+set DIRNAME=%~dp0
+if "%DIRNAME%" == "" set DIRNAME=.
+set APP_BASE_NAME=%~n0
+set APP_HOME=%DIRNAME%
+
+@rem Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+set DEFAULT_JVM_OPTS=
+
+@rem Find java.exe
+if defined JAVA_HOME goto findJavaFromJavaHome
+
+set JAVA_EXE=java.exe
+%JAVA_EXE% -version >NUL 2>&1
+if "%ERRORLEVEL%" == "0" goto init
+
+echo.
+echo ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+echo.
+echo Please set the JAVA_HOME variable in your environment to match the
+echo location of your Java installation.
+
+goto fail
+
+:findJavaFromJavaHome
+set JAVA_HOME=%JAVA_HOME:"=%
+set JAVA_EXE=%JAVA_HOME%/bin/java.exe
+
+if exist "%JAVA_EXE%" goto init
+
+echo.
+echo ERROR: JAVA_HOME is set to an invalid directory: %JAVA_HOME%
+echo.
+echo Please set the JAVA_HOME variable in your environment to match the
+echo location of your Java installation.
+
+goto fail
+
+:init
+@rem Get command-line arguments, handling Windows variants
+
+if not "%OS%" == "Windows_NT" goto win9xME_args
+
+:win9xME_args
+@rem Slurp the command line arguments.
+set CMD_LINE_ARGS=
+set _SKIP=2
+
+:win9xME_args_slurp
+if "x%~1" == "x" goto execute
+
+set CMD_LINE_ARGS=%*
+
+:execute
+@rem Setup the command line
+
+set CLASSPATH=%APP_HOME%\gradle\wrapper\gradle-wrapper.jar
+
+@rem Execute Gradle
+"%JAVA_EXE%" %DEFAULT_JVM_OPTS% %JAVA_OPTS% %GRADLE_OPTS% "-Dorg.gradle.appname=%APP_BASE_NAME%" -classpath "%CLASSPATH%" org.gradle.wrapper.GradleWrapperMain %CMD_LINE_ARGS%
+
+:end
+@rem End local scope for the variables with windows NT shell
+if "%ERRORLEVEL%"=="0" goto mainEnd
+
+:fail
+rem Set variable GRADLE_EXIT_CONSOLE if you need the _script_ return code instead of
+rem the _cmd.exe /c_ return code!
+if  not "" == "%GRADLE_EXIT_CONSOLE%" exit 1
+exit /b 1
+
+:mainEnd
+if "%OS%"=="Windows_NT" endlocal
+
+:omega
diff --git a/Chapter_04/aop/settings.gradle b/Chapter_04/aop/settings.gradle
new file mode 100644
index 0000000..683c3ed
--- /dev/null
+++ b/Chapter_04/aop/settings.gradle
@@ -0,0 +1,2 @@
+rootProject.name = 'aop'
+
diff --git a/Chapter_04/aop/src/main/java/concert/Audience.java b/Chapter_04/aop/src/main/java/concert/Audience.java
new file mode 100644
index 0000000..4e43a4c
--- /dev/null
+++ b/Chapter_04/aop/src/main/java/concert/Audience.java
@@ -0,0 +1,45 @@
+package concert;
+
+import org.aspectj.lang.ProceedingJoinPoint;
+import org.aspectj.lang.annotation.Around;
+import org.aspectj.lang.annotation.Aspect;
+import org.aspectj.lang.annotation.Pointcut;
+
+@Aspect
+public class Audience {
+    @Pointcut("execution(* concert.Performance.perform(..))")
+    public void performance() {
+    }
+
+    @Around("performance()")
+    public void watchPerformance(ProceedingJoinPoint jp) {
+        try {
+            System.out.println("Silencing cell phones");
+            System.out.println("Taking seats");
+            jp.proceed();
+            System.out.println("CLAP CLAP CLAP!!!");
+        } catch (Throwable e) {
+            System.out.println("Demanding a refund");
+        }
+    }
+
+//    @Before("performance()")
+//    public void silenceCellPhone() {
+//        System.out.println("Silencing cell phones");
+//    }
+//
+//    @Before("performance()")
+//    public void takeSeats() {
+//        System.out.println("Taking seats");
+//    }
+//
+//    @Before("performance()")
+//    public void applause() {
+//        System.out.println("CLAP CLAP CLAP!!!");
+//    }
+//
+//    @Before("performance()")
+//    public void demandRefund() {
+//        System.out.println("Demanding a refund");
+//    }
+}
diff --git a/Chapter_04/aop/src/main/java/concert/ConcertConfig.java b/Chapter_04/aop/src/main/java/concert/ConcertConfig.java
new file mode 100644
index 0000000..e2220f6
--- /dev/null
+++ b/Chapter_04/aop/src/main/java/concert/ConcertConfig.java
@@ -0,0 +1,22 @@
+package concert;
+
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.ComponentScan;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.context.annotation.EnableAspectJAutoProxy;
+
+@Configuration
+@EnableAspectJAutoProxy
+@ComponentScan
+public class ConcertConfig {
+
+    @Bean
+    public Audience audience() {
+        return new Audience();
+    }
+
+    @Bean
+    public EncoreableIntroducer encoreableIntroducer() {
+        return new EncoreableIntroducer();
+    }
+}
diff --git a/Chapter_04/aop/src/main/java/concert/DefaultEncoreable.java b/Chapter_04/aop/src/main/java/concert/DefaultEncoreable.java
new file mode 100644
index 0000000..d06729e
--- /dev/null
+++ b/Chapter_04/aop/src/main/java/concert/DefaultEncoreable.java
@@ -0,0 +1,8 @@
+package concert;
+
+public class DefaultEncoreable implements Encoreable {
+    @Override
+    public void performEncore() {
+        System.out.println("Default encoreable");
+    }
+}
diff --git a/Chapter_04/aop/src/main/java/concert/Encoreable.java b/Chapter_04/aop/src/main/java/concert/Encoreable.java
new file mode 100644
index 0000000..822ad00
--- /dev/null
+++ b/Chapter_04/aop/src/main/java/concert/Encoreable.java
@@ -0,0 +1,5 @@
+package concert;
+
+public interface Encoreable {
+    void performEncore();
+}
diff --git a/Chapter_04/aop/src/main/java/concert/EncoreableIntroducer.java b/Chapter_04/aop/src/main/java/concert/EncoreableIntroducer.java
new file mode 100644
index 0000000..d850a90
--- /dev/null
+++ b/Chapter_04/aop/src/main/java/concert/EncoreableIntroducer.java
@@ -0,0 +1,11 @@
+package concert;
+
+import org.aspectj.lang.annotation.Aspect;
+import org.aspectj.lang.annotation.DeclareParents;
+
+@Aspect
+public class EncoreableIntroducer {
+
+    @DeclareParents(value = "concert.Performance+", defaultImpl = DefaultEncoreable.class)
+    public static Encoreable encoreable;
+}
diff --git a/Chapter_04/aop/src/main/java/concert/Music.java b/Chapter_04/aop/src/main/java/concert/Music.java
new file mode 100644
index 0000000..c1450bd
--- /dev/null
+++ b/Chapter_04/aop/src/main/java/concert/Music.java
@@ -0,0 +1,11 @@
+package concert;
+
+import org.springframework.stereotype.Component;
+
+@Component
+public class Music implements Performance {
+    @Override
+    public void perform() {
+        System.out.println("Piano Solo");
+    }
+}
diff --git a/Chapter_04/aop/src/main/java/concert/Performance.java b/Chapter_04/aop/src/main/java/concert/Performance.java
new file mode 100644
index 0000000..7654ce3
--- /dev/null
+++ b/Chapter_04/aop/src/main/java/concert/Performance.java
@@ -0,0 +1,5 @@
+package concert;
+
+public interface Performance {
+    void perform();
+}
\ No newline at end of file
diff --git a/Chapter_04/aop/src/main/java/params/BlankDisc.java b/Chapter_04/aop/src/main/java/params/BlankDisc.java
new file mode 100644
index 0000000..8cf45f9
--- /dev/null
+++ b/Chapter_04/aop/src/main/java/params/BlankDisc.java
@@ -0,0 +1,33 @@
+package params;
+
+import java.util.List;
+
+public class BlankDisc implements CompactDisc {
+
+    private String title;
+    private String artist;
+    private List<String> tracks;
+
+    public void setTitle(String title) {
+        this.title = title;
+    }
+
+    public void setArtist(String artist) {
+        this.artist = artist;
+    }
+
+    public void setTracks(List<String> tracks) {
+        this.tracks = tracks;
+    }
+
+    public void play() {
+        System.out.println("Playing " + title + " by " + artist);
+        for (int i = 0; i < tracks.size(); i++) {
+            playTrack(i);
+        }
+    }
+
+    public void playTrack(int track) {
+        System.out.println("-Track: " + tracks.get(track));
+    }
+}
diff --git a/Chapter_04/aop/src/main/java/params/CompactDisc.java b/Chapter_04/aop/src/main/java/params/CompactDisc.java
new file mode 100644
index 0000000..21bc2c3
--- /dev/null
+++ b/Chapter_04/aop/src/main/java/params/CompactDisc.java
@@ -0,0 +1,7 @@
+package params;
+
+public interface CompactDisc {
+    void play();
+
+    void playTrack(int track);
+}
\ No newline at end of file
diff --git a/Chapter_04/aop/src/main/java/params/TrackCounter.java b/Chapter_04/aop/src/main/java/params/TrackCounter.java
new file mode 100644
index 0000000..78b36bf
--- /dev/null
+++ b/Chapter_04/aop/src/main/java/params/TrackCounter.java
@@ -0,0 +1,28 @@
+package params;
+
+import org.aspectj.lang.annotation.Aspect;
+import org.aspectj.lang.annotation.Before;
+import org.aspectj.lang.annotation.Pointcut;
+
+import java.util.HashMap;
+import java.util.Map;
+
+@Aspect
+public class TrackCounter {
+
+    private Map<Integer, Integer> trackCounts = new HashMap<>();
+
+    @Pointcut("execution(* params.CompactDisc.playTrack(int)) && args(trackNumber)")
+    public void trackPlayed(int trackNumber) {
+    }
+
+    @Before("trackPlayed(trackNumber)")
+    public void countTrack(int trackNumber) {
+        int currentCount = getPlayCount(trackNumber);
+        trackCounts.put(trackNumber, currentCount + 1);
+    }
+
+    public int getPlayCount(int trackNumber) {
+        return trackCounts.containsKey(trackNumber) ? trackCounts.get(trackNumber) : 0;
+    }
+}
diff --git a/Chapter_04/aop/src/main/java/params/TrackCounterConfig.java b/Chapter_04/aop/src/main/java/params/TrackCounterConfig.java
new file mode 100644
index 0000000..3bffef1
--- /dev/null
+++ b/Chapter_04/aop/src/main/java/params/TrackCounterConfig.java
@@ -0,0 +1,42 @@
+package params;
+
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.context.annotation.EnableAspectJAutoProxy;
+
+import java.util.ArrayList;
+import java.util.List;
+
+@Configuration
+@EnableAspectJAutoProxy
+public class TrackCounterConfig {
+
+    @Bean
+    public CompactDisc blankDisc() {
+        BlankDisc cd = new BlankDisc();
+        cd.setTitle("Sgt. Pepper's Lonely Hearts Club Band");
+        cd.setArtist("The Beatles");
+
+        List<String> tracks = new ArrayList<>();
+        tracks.add("Sgt. Pepper's Lonely Hearts Club Band");
+        tracks.add("With a Little Help from My Friends");
+        tracks.add("Lucy in the Sky with Diamonds");
+        tracks.add("Getting Better");
+        tracks.add("Fixing a Hole");
+        tracks.add("She's Leaving Home");
+        tracks.add("Within You Without You");
+        tracks.add("When I'm Sixty-Four");
+        tracks.add("Lovely Rita");
+        tracks.add("Good Morning Good Morning");
+        tracks.add("A Day in the Life");
+
+        cd.setTracks(tracks);
+
+        return cd;
+    }
+
+    @Bean
+    public TrackCounter trackCounter() {
+        return new TrackCounter();
+    }
+}
diff --git a/Chapter_04/aop/src/test/java/concert/ConcertTest.java b/Chapter_04/aop/src/test/java/concert/ConcertTest.java
new file mode 100644
index 0000000..5bac278
--- /dev/null
+++ b/Chapter_04/aop/src/test/java/concert/ConcertTest.java
@@ -0,0 +1,30 @@
+package concert;
+
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.test.context.ContextConfiguration;
+import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
+import org.junit.contrib.java.lang.system.StandardOutputStreamLog;
+
+import static org.junit.Assert.assertEquals;
+
+@RunWith(SpringJUnit4ClassRunner.class)
+@ContextConfiguration(classes = ConcertConfig.class)
+public class ConcertTest {
+    @Rule
+    public final StandardOutputStreamLog log = new StandardOutputStreamLog();
+
+    @Autowired
+    private Performance performance;
+
+    @Test
+    public void testPerformance() {
+        performance.perform();
+        assertEquals("Silencing cell phones\n" +
+                "Taking seats\n" +
+                "Piano Solo\n" +
+                "CLAP CLAP CLAP!!!\n", log.getLog());
+    }
+}
diff --git a/Chapter_04/aop/src/test/java/concert/EncoreableTest.java b/Chapter_04/aop/src/test/java/concert/EncoreableTest.java
new file mode 100644
index 0000000..ec7513c
--- /dev/null
+++ b/Chapter_04/aop/src/test/java/concert/EncoreableTest.java
@@ -0,0 +1,27 @@
+package concert;
+
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.contrib.java.lang.system.StandardOutputStreamLog;
+import org.junit.runner.RunWith;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.test.context.ContextConfiguration;
+import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
+
+import static org.junit.Assert.assertEquals;
+
+@RunWith(SpringJUnit4ClassRunner.class)
+@ContextConfiguration(classes = ConcertConfig.class)
+public class EncoreableTest {
+    @Rule
+    public final StandardOutputStreamLog log = new StandardOutputStreamLog();
+
+    @Autowired
+    private Encoreable performance;
+
+    @Test
+    public void testPerformance() {
+        performance.performEncore();
+        assertEquals("Default encoreable\n", log.getLog());
+    }
+}
diff --git a/Chapter_04/aop/src/test/java/params/TrackCountTest.java b/Chapter_04/aop/src/test/java/params/TrackCountTest.java
new file mode 100644
index 0000000..b677b2a
--- /dev/null
+++ b/Chapter_04/aop/src/test/java/params/TrackCountTest.java
@@ -0,0 +1,40 @@
+package params;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.test.context.ContextConfiguration;
+import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
+
+import static org.junit.Assert.assertEquals;
+
+@RunWith(SpringJUnit4ClassRunner.class)
+@ContextConfiguration(classes = TrackCounterConfig.class)
+public class TrackCountTest {
+    @Autowired
+    private CompactDisc cd;
+
+    @Autowired
+    private TrackCounter counter;
+
+    @Test
+    public void testTrackCounter() {
+        cd.playTrack(1);
+        cd.playTrack(2);
+        cd.playTrack(3);
+        cd.playTrack(3);
+        cd.playTrack(3);
+        cd.playTrack(3);
+        cd.playTrack(6);
+        cd.playTrack(7);
+        cd.playTrack(7);
+
+        assertEquals(1, counter.getPlayCount(1));
+        assertEquals(1, counter.getPlayCount(2));
+        assertEquals(4, counter.getPlayCount(3));
+        assertEquals(0, counter.getPlayCount(4));
+        assertEquals(0, counter.getPlayCount(5));
+        assertEquals(1, counter.getPlayCount(6));
+        assertEquals(2, counter.getPlayCount(7));
+    }
+}