/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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.commons.chain.generic;
import org.apache.commons.chain.Command;
import org.apache.commons.chain.Context;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.Map;
import java.util.WeakHashMap;
/**
* An abstract base command which uses introspection to look up a method to execute.
* For use by developers who prefer to group related functionality into a single class
* rather than an inheritance family.
*
* @since Chain 1.1
*/
public abstract class DispatchCommand implements Command {
/** Cache of methods */
private Map methods = new WeakHashMap();
/** Method name */
private String method = null;
/** Method key */
private String methodKey = null;
/**
* The base implementation expects dispatch methods to take a <code>Context</code>
* as their only argument.
*/
protected static final Class[] DEFAULT_SIGNATURE = new Class[] {Context.class};
/**
* Look up the method specified by either "method" or "methodKey" and invoke it,
* returning a boolean value as interpreted by <code>evaluateResult</code>.
* @param context The Context to be processed by this Command.
* @return the result of method being dispatched to.
* @throws IllegalStateException if neither 'method' nor 'methodKey' properties are defined
* @throws Exception if any is thrown by the invocation. Note that if invoking the method
* results in an InvocationTargetException, the cause of that exception is thrown instead of
* the exception itself, unless the cause is an <code>Error</code> or other <code>Throwable</code>
* which is not an <code>Exception</code>.
*/
public boolean execute(Context context) throws Exception {
if (this.getMethod() == null && this.getMethodKey() == null) {
throw new IllegalStateException("Neither 'method' nor 'methodKey' properties are defined ");
}
Method methodObject = extractMethod(context);
try {
return evaluateResult(methodObject.invoke(this, getArguments(context)));
} catch (InvocationTargetException e) {
Throwable cause = e.getTargetException();
if (cause instanceof Exception) {
throw (Exception)cause;
}
throw e;
}
}
/**
* Extract the dispatch method. The base implementation uses the command's
* <code>method</code> property as the name of a method to look up, or, if that is not defined,
* looks up the the method name in the Context using the <code>methodKey</code>.
*
* @param context The Context being processed by this Command.
* @return The method to execute
* @throws NoSuchMethodException if no method can be found under the specified name.
* @throws NullPointerException if no methodName cannot be determined
*/
protected Method extractMethod(Context context) throws NoSuchMethodException {
String methodName = this.getMethod();
if (methodName == null) {
Object methodContextObj = context.get(this.getMethodKey());
if (methodContextObj == null) {
throw new NullPointerException("No value found in context under " + this.getMethodKey());
}
methodName = methodContextObj.toString();
}
Method theMethod = null;
synchronized (methods) {
theMethod = (Method) methods.get(methodName);
if (theMethod == null) {
theMethod = getClass().getMethod(methodName, getSignature());
methods.put(methodName, theMethod);
}
}
return theMethod;
}
/**
* Evaluate the result of the method invocation as a boolean value. Base implementation
* expects that the invoked method returns boolean true/false, but subclasses might
* implement other interpretations.
* @param o The result of the methid execution
* @return The evaluated result/
*/
protected boolean evaluateResult(Object o) {
Boolean result = (Boolean) o;
return (result != null && result.booleanValue());
}
/**
* Return a <code>Class[]</code> describing the expected signature of the method.
* @return The method signature.
*/
protected Class[] getSignature() {
return DEFAULT_SIGNATURE;
}
/**
* Get the arguments to be passed into the dispatch method.
* Default implementation simply returns the context which was passed in, but subclasses
* could use this to wrap the context in some other type, or extract key values from the
* context to pass in. The length and types of values returned by this must coordinate
* with the return value of <code>getSignature()</code>
* @param context The Context being processed by this Command.
* @return The method arguments.
*/
protected Object[] getArguments(Context context) {
return new Object[] {context};
}
/**
* Return the method name.
* @return The method name.
*/
public String getMethod() {
return method;
}
/**
* Return the Context key for the method name.
* @return The Context key for the method name.
*/
public String getMethodKey() {
return methodKey;
}
/**
* Set the method name.
* @param method The method name.
*/
public void setMethod(String method) {
this.method = method;
}
/**
* Set the Context key for the method name.
* @param methodKey The Context key for the method name.
*/
public void setMethodKey(String methodKey) {
this.methodKey = methodKey;
}
}