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Groovy: A powerful, dynamic language for the JVM
There is a newer version: 3.0.21
/*
 * Copyright 2003-2007 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 groovy.lang;

import java.io.IOException;
import java.io.PrintWriter;
import java.io.Writer;

/*
 * This {@link Interceptor} traces method calls on the proxied object to a log. 
 * By default, the log is simply System.out; however, that can be 
 * changed with the setWriter(Writer)
 method. 


 * 
 * A message will be written to output before a method is invoked and after a method
 * is invoked. If methods are nested, and invoke one another, then indentation 
 * of two spaces is written. 


 *
 * Here is an example usage on the ArrayList object: 

 *  * def proxy = ProxyMetaClass.getInstance(ArrayList.class)
 * proxy.interceptor = new TracingInterceptor()
 * proxy.use {
 *     def list = [1, 2, 3]
 *     assert 3 == list.size()
 *     assert list.contains(1)
 * }
 * 
 * Running this code produces this output: 
 *  * before java.util.ArrayList.size()
 * after  java.util.ArrayList.size()
 * before java.util.ArrayList.contains(java.lang.Integer)
 * after  java.util.ArrayList.contains(java.lang.Integer)
 * 
 */
public class TracingInterceptor implements Interceptor {

    protected Writer writer = new PrintWriter(System.out);
    private int indent = 0;

    /**
    * Returns the writer associated with this interceptor. 
    */ 
    public Writer getWriter() {
        return writer;
    }

    /**
    * Changes the writer associated with this interceptor. 
    */ 
    public void setWriter(Writer writer) {
        this.writer = writer;
    }

    public Object beforeInvoke(Object object, String methodName, Object[] arguments) {
        write(object, methodName, arguments, "before");
        indent++ ;
        return null;
    }

    public Object afterInvoke(Object object, String methodName, Object[] arguments, Object result) {
        indent--;
        write(object, methodName, arguments, "after ");
        return result;
    }

    public boolean doInvoke() {
        return true;
    }
    private String indent(){
        StringBuffer result = new StringBuffer();
        for (int i=0; i 0) writer.write(", ");
            Object argument = arguments[i];
            writer.write(argument.getClass().getName());
        }
        writer.write(")");
    }
}