FilenameFilter学习

从给定的一个路径中筛选中某种格式的文件，通常的做法，便是遍历该目录，然后按照文件后缀来判断该文件是否符合判断条件。

public class FileFilter {

	public static void main(String[] args) {
		File filepath = new File("F:\\论文\\中国知网论文\\中国知网论文");
		List<File> list = filterFile(filepath);
		System.out.println(list.size());
	}

	public static List<File> filterFile(File file) {
		List<File> list = new ArrayList<File>();
		File[] fileList = file.listFiles();
		for (int i = 0; i < fileList.length; i++) {
			// 判断该file是否是目录，是目录，则继续深入遍历
			if (fileList[i].isDirectory()) {
				filterFile(fileList[i]);
			// 是文件时，判断后缀是否是PDF结尾，是则截取出来该文件
			} else if (fileList[i].getName().endsWith(".pdf")) {
				list.add(fileList[i]);
			}
			else
				continue;
		}

		return list;
	}
}

其实 java的File 类有一个自带的过滤方法，即FilenameFilter接口

FilenameFilter接口自带一个accept方法，过滤符合条件的文件类型

package java.io;

/**
 * Instances of classes that implement this interface are used to
 * filter filenames. These instances are used to filter directory
 * listings in the <code>list</code> method of class
 * <code>File</code>, and by the Abstract Window Toolkit's file
 * dialog component.
 *
 * @author  Arthur van Hoff
 * @author  Jonathan Payne
 * @see     java.awt.FileDialog#setFilenameFilter(java.io.FilenameFilter)
 * @see     java.io.File
 * @see     java.io.File#list(java.io.FilenameFilter)
 * @since   JDK1.0
 */
public interface FilenameFilter {
    /**
     * Tests if a specified file should be included in a file list.
     *
     * @param   dir    the directory in which the file was found.
     * @param   name   the name of the file.
     * @return  <code>true</code> if and only if the name should be
     * included in the file list; <code>false</code> otherwise.
     */
    boolean accept(File dir, String name);
}

FilenameFilter 接口中的accept方法，主要判断给定的文件是否包含在该目录中

通过FilenameFilter 接口改造后的代码

public class FileFilter {

	public static void main(String[] args) {
		File filepath = new File("F:\\论文\\中国知网论文\\中国知网论文");
		List<File> list = filterFile(filepath);
		System.out.println(list.size());
	}

	public static List<File> filterFile(File file) {
		// 定义变量list来接收最后的文件列表
		List<File> list = new ArrayList<File>();

		// 将文件类型给到FilterName 中
		FilterName filter = new FilterName(".abcd"); 

		// 文件过滤
        String[] files = file.list(filter);  

        // 由于File.list(FilenameFilter filter) 返回结果为数组
        // 此处将数组转换为list
        if (null != files) {
            for (String fileName : files) {
            	list.add(new File(fileName));
            }
        }

		return list;
	}
}

class FilterName implements FilenameFilter {

	private String type;

	// 构造方法，定义要过滤的文件类型
    FilterName(String type) {
    	this.type = type;
    }

	@Override
	public boolean accept(File dir, String name) {
		return name.endsWith(type);
	}
}