src/examples/plugins/pipeline/Pipeline.java

/*
 * 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</code>.
 * <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 + ".");
    }
}