java io 之File类

1.1File类

File 类这个名称有一定的误导性，她既可以代表一个特定的文件(eg:F:\JMS\apache-activemq-5.7.0\bin\activemq.bat)；又可以代表某个目录下的一组文件(eg:F:\JMS\apache-activemq-5.7.0)

文件过滤器

有些时候，我们需要获取指定目录下的一些文件，比如F:\javastudy\io目录下所有java文件。请看如下示例

import java.io.File;
import java.util.regex.Pattern;
public class FileList {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		File file=new File("F:"+File.separator+"javastudy"+File.separator+"io");
		String[] fileNames=file.list(new FileFilter(".java"));
		for(String item:fileNames){
			System.out.println(item);
		}
	}

}
class FileFilter implements java.io.FilenameFilter{
	private String filterName;
	public FileFilter(String filterName){
		this.filterName=filterName;
	}
	@Override
	public boolean accept(File dir, String name) {
		if(name.endsWith(filterName)){
			return true;
		}
		return false;
	}
	
}
class FileFilter1 implements java.io.FilenameFilter{
	private Pattern pattern;
	public FileFilter1(String regex){
		this.pattern=Pattern.compile(regex);
	}
	@Override
	public boolean accept(File dir, String name) {
		return pattern.matcher(name).matches();
	}
	
}

先看下File类中list(FilenamFilterfilter)方法,源码如下：

public String[] list(FilenameFilter filter) {
		String names[] = list();
		if ((names == null) || (filter == null)) {
			return names;
		}
		ArrayList v = new ArrayList();
		for (int i = 0 ; i < names.length ; i++) {
			if (filter.accept(this, names[i])) {
				v.add(names[i]);
			}
		}
		return (String[])(v.toArray(new String[v.size()]));
	}

list()方法会为此目录下的每个文件名调用accept()方法，来判断该文件是否包含在内。

类FileFilter 实现了FilenameFilter接口,这个接口只需实现accept方法

目录实用工具

import java.io.File;
import java.io.FilenameFilter;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Iterator;
import java.util.List;
import java.util.regex.Pattern;
public final class Directory {
	public static final 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) {
				
				return pattern.matcher(new File(name).getName()).matches();
			}
		});
	}
	public static final File[] local(String path,final String regex){
		return local(new File(path),regex);
	}
	public static class TreeInfo implements Iterable<File>{
		private List<File> dirs=new ArrayList<File>();
		private List<File> files=new ArrayList<File>();
		@Override
		public Iterator<File> iterator() {

			return files.iterator();
		}
		void addAll(TreeInfo other){
			dirs.addAll(other.dirs);
			files.addAll(other.files);
		}
		@Override
		public String toString() {
			return "dirs:"+PPrint.pFormat(dirs)+"\nfiles:"+PPrint.pFormat(files);
		}
		
		public static TreeInfo walk(File start,String regex){
			return recurseDirs(start,regex);
		}
		
		public static TreeInfo walk(String start,String regex){
			return recurseDirs(new File(start),regex);
		}
		public static TreeInfo walk(File start){
			return recurseDirs(start,".*");
		}
		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;
		}
		public static void main(String[] args) {
			System.out.println(walk("F:/javastudy"));
		}
	}
	
}
class PPrint{
	public static String pFormat(Collection<?> c){
		if(c.size()==0)return "[]";
		StringBuilder result=new StringBuilder("[");
		for(Object item:c){
			if(c.size()!=1){
				result.append("\n");
			}
			result.append(item);
		}
		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)));
	}
}

运行结果如下：