对程序语言的设计者来说，创建一个好的输出/输入（I/O）系统是一项艰难的任务。——《Thinking in Java》

18.1 File类

18.1.1 目录列表器

Directory.java

package com.ntech.io;

import java.io.File;
import java.io.FilenameFilter;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.regex.Pattern;

/**
 * 目录实用工具类
 * @author joiant
 *
 */
public final class Directory {

    public static void main(String[] args) {
        System.out.println(walk("."));

    }

    /**
     * 根据正则表达式匹配文件,获得File数组
     * @param dir
     * @param regex
     * @return
     */
    public static File[] local(File dir, final String regex) {
        return dir.listFiles(new FilenameFilter() {
            private Pattern pattern = Pattern.compile(regex);
            @Override
            public boolean accept(File dir, String name) {
                // TODO Auto-generated method stub
                return pattern.matcher(new File(name).getName()).matches();
            }
            
        });
    }
    
    /**
     * Overloaded
     * @param path
     * @param regex
     * @return
     */
    public static File[] local(String path, final String regex) {
        return local(new File(path), regex);
    }
    
    /**
     * 实现了Iterable<File>
     * @author joiant
     *
     */
    public static class TreeInfo implements Iterable<File>{
        public List<File> files = new ArrayList<File>();
        public List<File> dirs = new ArrayList<File>();
        @Override
        public Iterator<File> iterator() {
            // TODO Auto-generated method stub
            return files.iterator();
        }
        
        void addAll(TreeInfo other) {
            files.addAll(other.files);
            dirs.addAll(other.dirs);
        }
        
        public String toString() {
            return "dirs: " + PPrint.pformat(dirs) + "\n\n" 
                    + "files: " + PPrint.pformat(files);
        }   
    }
    
    /**
     * 将目录名字转化为File对象
     * @param start
     * @param regex
     * @return
     */
    public static TreeInfo walk(String start, String regex) {
        return recurseDirs(new File(start), regex);
    }
    
    public static TreeInfo walk(File start, String regex) {
        return recurseDirs(start, regex);
    }
    
    public static TreeInfo walk(String start) {
        return recurseDirs(new File(start), ".*");
    }
    
    static TreeInfo recurseDirs(File startDir, String regex) {
        TreeInfo result = new TreeInfo();
        for(File item : startDir.listFiles()) {
            if(item.isDirectory()) {
                result.dirs.add(item);
                result.addAll(recurseDirs(item, regex));
            }else if(item.getName().matches(regex)) {
                result.files.add(item);
            }
        }
        return result;
    }
}

PPrint.java

package com.ntech.io;

import java.util.Arrays;
import java.util.Collection;

/**
 * "灵巧打印机"
 * @author joiant
 *
 */
public class PPrint {
    public static String pformat(Collection<?> c) {
        if(c.size() == 0) {
            return "[]";
        }
        StringBuilder result = new StringBuilder("[");
        for(Object elem : c) {
            if(c.size() != 1) {
                result.append("\n  ");
            }
            result.append(elem);
        }
        if(c.size() != 1) {
            result.append("\n");
        }
        result.append("]");
        return result.toString();
    }
    
    public static void pprint(Collection<?> c) {
        System.out.println(pformat(c));
    }
    
    public static void pprint(Object[] c) {
        System.out.println(pformat(Arrays.asList(c)));
    }
}

ProcessFiles.java

package com.ntech.io;

import java.io.File;
import java.io.IOException;

public class ProcessFiles {
    public interface Strategy{
        void process(File file);
    }
    
    private Strategy strategy;
    private String ext;
    public ProcessFiles(Strategy strategy, String ext) {
        this.strategy = strategy;
        this.ext = ext;
    }
    
    public void start(String[] args) throws IOException {
        if(args.length ==0) {
            processDirectoryTree(new File("."));
        }else {
            for(String arg: args) {
                File fileArg = new File(arg);
                if(fileArg.isDirectory()) {
                    processDirectoryTree(fileArg);
                }else {
                    if(!arg.endsWith("." + ext)) {
                        arg += "." + ext;
                    }
                    strategy.process(new File(arg).getCanonicalFile());
                }
            }
        }
    }
    
    public void processDirectoryTree(File root) throws IOException {
        for(File file:Directory.walk(root.getAbsolutePath(), ".*\\." + ext)) {
            strategy.process(file.getCanonicalFile());
        }
    }
    
    public static void main(String[] args) throws IOException {
        new ProcessFiles(new Strategy() {
            
            @Override
            public void process(File file) {
                System.out.println(file);
                
            }
        }, "java").start(args);
    }
}