Allow to specify a default value on placeholder

fix gh-852

Author: kazuki43zoo

src/main/java/org/apache/ibatis/parsing/PropertyParser.java

@@ -1,5 +1,5 @@
 /**
- *    Copyright 2009-2015 the original author or authors.
+ *    Copyright 2009-2016 the original author or authors.
  *
  *    Licensed under the Apache License, Version 2.0 (the "License");
  *    you may not use this file except in compliance with the License.
@@ -19,9 +19,33 @@
 
 /**
  * @author Clinton Begin
+ * @author Kazuki Shimizu
  */
 public class PropertyParser {
 
+  private static final String KEY_PREFIX = "org.apache.ibatis.parsing.PropertyParser.";
+  /**
+   * The special property key that indicate whether enable a default value on placeholder.
+   * <p>
+   *   The default value is {@code false} (indicate disable a default value on placeholder)
+   *   If you specify the {@code true}, you can specify key and default value on placeholder (e.g. {@code ${db.username:postgres}}).
+   * </p>
+   * @since 3.4.2
+   */
+  public static final String KEY_ENABLE_DEFAULT_VALUE = KEY_PREFIX + "enable-default-value";
+
+  /**
+   * The special property key that specify a separator for key and default value on placeholder.
+   * <p>
+   *   The default separator is {@code ":"}.
+   * </p>
+   * @since 3.4.2
+   */
+  public static final String KEY_DEFAULT_VALUE_SEPARATOR = KEY_PREFIX + "default-value-separator";
+
+  private static final String ENABLE_DEFAULT_VALUE = "false";
+  private static final String DEFAULT_VALUE_SEPARATOR = ":";
+
   private PropertyParser() {
     // Prevent Instantiation
   }
@@ -33,18 +57,41 @@ public static String parse(String string, Properties variables) {
   }
 
   private static class VariableTokenHandler implements TokenHandler {
-    private Properties variables;
+    private final Properties variables;
+    private final boolean enableDefaultValue;
+    private final String defaultValueSeparator;
 
-    public VariableTokenHandler(Properties variables) {
+    private VariableTokenHandler(Properties variables) {
       this.variables = variables;
+      this.enableDefaultValue = Boolean.parseBoolean(getPropertyValue(KEY_ENABLE_DEFAULT_VALUE, ENABLE_DEFAULT_VALUE));
+      this.defaultValueSeparator = getPropertyValue(KEY_DEFAULT_VALUE_SEPARATOR, DEFAULT_VALUE_SEPARATOR);
+    }
+
+    private String getPropertyValue(String key, String defaultValue) {
+      return (variables == null) ? defaultValue : variables.getProperty(key, defaultValue);
     }
 
     @Override
     public String handleToken(String content) {
-      if (variables != null && variables.containsKey(content)) {
-        return variables.getProperty(content);
+      if (variables != null) {
+        String key = content;
+        if (enableDefaultValue) {
+          final int separatorIndex = content.indexOf(defaultValueSeparator);
+          String defaultValue = null;
+          if (separatorIndex >= 0) {
+            key = content.substring(0, separatorIndex);
+            defaultValue = content.substring(separatorIndex + defaultValueSeparator.length());
+          }
+          if (defaultValue != null) {
+            return variables.getProperty(key, defaultValue);
+          }
+        }
+        if (variables.containsKey(key)) {
+          return variables.getProperty(key);
+        }
       }
       return "${" + content + "}";
     }
   }
+
 }

src/test/java/org/apache/ibatis/parsing/PropertyParserTest.java

@@ -0,0 +1,84 @@
+/**
+ *    Copyright 2009-2016 the original author or authors.
+ *
+ *    Licensed under the Apache License, Version 2.0 (the "License");
+ *    you may not use this file except in compliance with the License.
+ *    You may obtain a copy of the License at
+ *
+ *       http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *    Unless required by applicable law or agreed to in writing, software
+ *    distributed under the License is distributed on an "AS IS" BASIS,
+ *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *    See the License for the specific language governing permissions and
+ *    limitations under the License.
+ */
+package org.apache.ibatis.parsing;
+
+import org.hamcrest.core.Is;
+import org.junit.Assert;
+import org.junit.Test;
+
+import java.util.Properties;
+
+public class PropertyParserTest {
+
+  @Test
+  public void replaceToVariableValue() {
+    Properties props = new Properties();
+    props.setProperty(PropertyParser.KEY_ENABLE_DEFAULT_VALUE, "true");
+    props.setProperty("key", "value");
+    props.setProperty("tableName", "members");
+    props.setProperty("orderColumn", "member_id");
+    props.setProperty("a:b", "c");
+    Assert.assertThat(PropertyParser.parse("${key}", props), Is.is("value"));
+    Assert.assertThat(PropertyParser.parse("${key:aaaa}", props), Is.is("value"));
+    Assert.assertThat(PropertyParser.parse("SELECT * FROM ${tableName:users} ORDER BY ${orderColumn:id}", props), Is.is("SELECT * FROM members ORDER BY member_id"));
+
+    props.setProperty(PropertyParser.KEY_ENABLE_DEFAULT_VALUE, "false");
+    Assert.assertThat(PropertyParser.parse("${a:b}", props), Is.is("c"));
+
+    props.remove(PropertyParser.KEY_ENABLE_DEFAULT_VALUE);
+    Assert.assertThat(PropertyParser.parse("${a:b}", props), Is.is("c"));
+
+  }
+
+  @Test
+  public void notReplace() {
+    Properties props = new Properties();
+    props.setProperty(PropertyParser.KEY_ENABLE_DEFAULT_VALUE, "true");
+    Assert.assertThat(PropertyParser.parse("${key}", props), Is.is("${key}"));
+    Assert.assertThat(PropertyParser.parse("${key}", null), Is.is("${key}"));
+
+    props.setProperty(PropertyParser.KEY_ENABLE_DEFAULT_VALUE, "false");
+    Assert.assertThat(PropertyParser.parse("${a:b}", props), Is.is("${a:b}"));
+
+    props.remove(PropertyParser.KEY_ENABLE_DEFAULT_VALUE);
+    Assert.assertThat(PropertyParser.parse("${a:b}", props), Is.is("${a:b}"));
+
+  }
+
+  @Test
+  public void applyDefaultValue() {
+    Properties props = new Properties();
+    props.setProperty(PropertyParser.KEY_ENABLE_DEFAULT_VALUE, "true");
+    Assert.assertThat(PropertyParser.parse("${key:default}", props), Is.is("default"));
+    Assert.assertThat(PropertyParser.parse("SELECT * FROM ${tableName:users} ORDER BY ${orderColumn:id}", props), Is.is("SELECT * FROM users ORDER BY id"));
+    Assert.assertThat(PropertyParser.parse("${key:}", props), Is.is(""));
+    Assert.assertThat(PropertyParser.parse("${key: }", props), Is.is(" "));
+    Assert.assertThat(PropertyParser.parse("${key::}", props), Is.is(":"));
+  }
+
+  @Test
+  public void applyCustomSeparator() {
+    Properties props = new Properties();
+    props.setProperty(PropertyParser.KEY_ENABLE_DEFAULT_VALUE, "true");
+    props.setProperty(PropertyParser.KEY_DEFAULT_VALUE_SEPARATOR, "?:");
+    Assert.assertThat(PropertyParser.parse("${key?:default}", props), Is.is("default"));
+    Assert.assertThat(PropertyParser.parse("SELECT * FROM ${schema?:prod}.${tableName == null ? 'users' : tableName} ORDER BY ${orderColumn}", props), Is.is("SELECT * FROM prod.${tableName == null ? 'users' : tableName} ORDER BY ${orderColumn}"));
+    Assert.assertThat(PropertyParser.parse("${key?:}", props), Is.is(""));
+    Assert.assertThat(PropertyParser.parse("${key?: }", props), Is.is(" "));
+    Assert.assertThat(PropertyParser.parse("${key?::}", props), Is.is(":"));
+  }
+
+}