Commons Digester example source code file (Pipeline.java)

This example Commons Digester source code file (Pipeline.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Commons Digester tags/keywords

bufferedreader, contents, digester, filereader, filereader, filewriter, io, ioexception, pipeline, pipeline, pluginrules, pluginrules, string, string, transform

The Commons Digester Pipeline.java source code

/*
 * 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.
 */ 

import org.apache.commons.digester.Digester;
import org.apache.commons.digester.plugins.PluginRules;
import org.apache.commons.digester.plugins.PluginCreateRule;
import java.io.*;

/**
 * This is the "main" class for this example.
 * <p>
 * It can be run via <code>java Pipeline config-file-name.
 * <p>
 * The specified config file is parsed using the Apache Commons Digester.
 * This config file specifies an input file to be read, a number of
 * user-defined transform classes to be instantiated and configured from
 * the config file, and an output file.
 * <p>
 * The contents of the input file is then passed to the transform objects,
 * and the output written to the output file. 
 * <p>
 * Why not try writing your own transform classes, and plugging them in.
 * Note that they can configure themselves from the main config file in
 * any manner the Digester supports, without changing a line of this
 * application.
 */
 
public class Pipeline {
    
    private String source;
    private String dest;
    private Transform transformer;

    public static void main(String[] args) {
        if (args.length != 1) {
            System.err.println("usage: pipeline config-file");
            System.exit(-1);
        }
        String configFile = args[0];
        
        Digester digester = new Digester();
        PluginRules rc = new PluginRules();
        digester.setRules(rc);
        
        digester.addObjectCreate("pipeline", Pipeline.class);
        
        digester.addCallMethod("pipeline/source", "setSource", 1);
        digester.addCallParam("pipeline/source", 0, "file");
        
        PluginCreateRule pcr = new PluginCreateRule(Transform.class);
        digester.addRule("pipeline/transform", pcr);
        digester.addSetNext("pipeline/transform", "setTransform");
        
        digester.addCallMethod("pipeline/destination", "setDest", 1);
        digester.addCallParam("pipeline/destination", 0, "file");
        
        Pipeline pipeline = null;
        try {
            pipeline = (Pipeline) digester.parse(configFile);
        }
        catch(Exception e) {
            System.err.println("oops exception occurred during parse.");
            e.printStackTrace();
            System.exit(-1);
        }
        
        try {
            pipeline.execute();
        }
        catch (Exception e) {
            System.err.println("oops exception occurred during pipeline execution.");
            e.printStackTrace();
            System.exit(-1);
        }
    }
    
    public void setSource(String source) {
        this.source = source;
    }
    
    public void setDest(String dest) {
        this.dest = dest;
    }
    
    public void setTransform(Transform transformer) {
        this.transformer = transformer;
    }
    
    private void execute() throws IOException {
        FileReader inRaw = new FileReader(source);
        FileWriter out = new FileWriter(dest);

        BufferedReader in = new BufferedReader(inRaw);
        
        while(true) {
            String inStr = in.readLine();
            if (inStr==null) 
                break;
            
            String outStr = transformer.transform(inStr);
            out.write(outStr);
            out.write('\n');
        }
        
        
        inRaw.close();
        out.close();
        
        System.out.println(
            "Contents of file " + source + " have been transformed, and"
            + " written to file " + dest + ".");
    }
}