Make DynamicLogLevelProcessor pluggable

Users can provide own subclasses of RequestLoggingFilter, which can
bring own implementations of DynLogEnvironment and DynLogLevelProcessor.
There are several constructors, that can be used to customize the filter.

Author: KarstenSchnitter

cf-java-logging-support-servlet/src/main/java/com/sap/hcp/cf/logging/servlet/dynlog/DynLogConfiguration.java

@@ -0,0 +1,17 @@
+package com.sap.hcp.cf.logging.servlet.dynlog;
+
+import java.security.interfaces.RSAPublicKey;
+
+import javax.servlet.http.HttpServletRequest;
+
+public interface DynLogConfiguration {
+
+    String getDynLogHeaderKey();
+
+    RSAPublicKey getRsaPublicKey();
+
+    default String getDynLogHeaderValue(HttpServletRequest httpRequest) {
+        return httpRequest.getHeader(getDynLogHeaderKey());
+    }
+
+}

cf-java-logging-support-servlet/src/main/java/com/sap/hcp/cf/logging/servlet/dynlog/DynLogEnvironment.java

@@ -10,7 +10,7 @@
 
 import com.sap.hcp.cf.logging.common.helper.Environment;
 
-public class DynLogEnvironment {
+public class DynLogEnvironment implements DynLogConfiguration {
 
     private static final Logger LOGGER = LoggerFactory.getLogger(DynLogEnvironment.class);
     private final RSAPublicKey rsaPublicKey;
@@ -46,10 +46,12 @@ public DynLogEnvironment() {
         }
     }
 
+    @Override
     public RSAPublicKey getRsaPublicKey() {
         return rsaPublicKey;
     }
 
+    @Override
     public String getDynLogHeaderKey() {
         return dynLogHeaderKey;
     }

cf-java-logging-support-servlet/src/main/java/com/sap/hcp/cf/logging/servlet/dynlog/DynamicLogLevelProcessor.java

@@ -3,8 +3,6 @@
 import java.util.Arrays;
 import java.util.List;
 
-import javax.servlet.http.HttpServletRequest;
-
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 import org.slf4j.MDC;
@@ -24,25 +22,22 @@ public class DynamicLogLevelProcessor {
     private static final List<String> ALLOWED_DYNAMIC_LOGLEVELS = Arrays.asList("TRACE", "DEBUG", "INFO", "WARN",
                                                                                 "ERROR");
     private final TokenDecoder tokenDecoder;
-    private final DynLogEnvironment dynLogEnvironment;
 
-    public DynamicLogLevelProcessor(DynLogEnvironment dynLogEnvironment) {
-        this.dynLogEnvironment = dynLogEnvironment;
-        this.tokenDecoder = new TokenDecoder(dynLogEnvironment.getRsaPublicKey());
+    public DynamicLogLevelProcessor(DynLogConfiguration dynLogConfig) {
+        this.tokenDecoder = new TokenDecoder(dynLogConfig.getRsaPublicKey());
     }
 
-    public void copyDynamicLogLevelToMDC(HttpServletRequest httpRequest) {
-        String logLevelToken = httpRequest.getHeader(dynLogEnvironment.getDynLogHeaderKey());
+    public void copyDynamicLogLevelToMDC(String logLevelToken) {
         if (logLevelToken == null) {
             return;
         } else {
             try {
                 DecodedJWT jwt = tokenDecoder.validateAndDecodeToken(logLevelToken);
                 String dynamicLogLevel = jwt.getClaim("level").asString();
-				String packages = jwt.getClaim("packages").asString();
+                String packages = jwt.getClaim("packages").asString();
                 if (ALLOWED_DYNAMIC_LOGLEVELS.contains(dynamicLogLevel)) {
                     MDC.put(DynamicLogLevelHelper.MDC_DYNAMIC_LOG_LEVEL_KEY, dynamicLogLevel);
-					MDC.put(DynamicLogLevelHelper.MDC_DYNAMIC_LOG_LEVEL_PREFIXES, packages);
+                    MDC.put(DynamicLogLevelHelper.MDC_DYNAMIC_LOG_LEVEL_PREFIXES, packages);
                 } else {
                     throw new DynamicLogLevelException("Dynamic Log-Level [" + dynamicLogLevel +
                                                        "] provided in header is not valid. Allowed Values are " +