案例

案例：复制单极文件夹

public class Demo07 {
    public static void main(String[] args) throws IOException {
        //创建数据源目录
        File srcFolder = new File("E:\\xiaobai");
        //取数据源目录名字，不包括文件名
        String srcFolderName = srcFolder.getName();
        //新建目标目录
        File destFoldername = new File(srcFolderName);
        //如果没有目标目录，则创建
        if (!destFoldername.exists()) {
            destFoldername.mkdir();
        }
        //列出源文件目录下所有目标文件，加入File集合
        File[] listFiles = srcFolder.listFiles();
        for (File srcFile : listFiles) {
            String srcFileName = srcFile.getName();//获取目标文件名
            File destfile = new File(destFoldername, srcFileName);//拼接目标目录名和目标文件名
            copyFile(srcFile, destfile);//调用方法复制文件
        }
    }

    //复制文件方法
    private static void copyFile(File srcFile, File destfile) throws IOException {
        BufferedInputStream bis = new BufferedInputStream(new FileInputStream(srcFile));
        BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream(destfile));
        byte[] by = new byte[1024];
        int len;
        while ((len = bis.read(by)) != -1) {
            bos.write(by, 0, len);
        }
        bis.close();
        bos.close();
    }
}

案例：复制多级文件夹

public class Demo08 {
    public static void main(String[] args) throws IOException {
        File srcFile = new File("E:\\xiaobai");//源文件路径
        File destFile = new File("F:\\");//目标文件路径
        copyFolder(srcFile, destFile);//调用复制目录方法
    }

    private static void copyFolder(File srcFile, File destFile) throws IOException{
        if (srcFile.isDirectory()) { //判断路径是否为目录，如果是，执行执行体内容
            String srcFileName = srcFile.getName();//获取源路径下目录名
            File newFolder = new File(destFile, srcFileName);//拼接新的目录名
            //如果该目录不存在，则创建目录
            if (!newFolder.exists()) {
                newFolder.mkdir(); 
            }
            File[] fileArray = srcFile.listFiles();//获取源路径下所有目录/文件，创建File数组
            for (File file : fileArray) {
                copyFolder(file,newFolder);//递归调用复制目录方法！！！！！！！
            }
        }else {
            //如果当前路径非目录，则获取文件名，拼接后调用复制文件方法
            File newFile = new File(destFile, srcFile.getName());
            copyFile(srcFile,newFile);
        }
    }

    private static void copyFile(File srcFile, File file) throws IOException {
        BufferedInputStream bis = new BufferedInputStream(new FileInputStream(srcFile));
        BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream(file));
        byte[] by = new byte[1024];
        int len;
        while ((len = bis.read(by)) != -1) {
            bos.write(by, 0, len);
        }
        bis.close();
        bos.close();
    }
}

复制文件的异常处理

利用try catch处理

public class Demo09 {
    public static void main(String[] args) {
        BufferedReader br = null;
        BufferedWriter bw = null;
        try {
            br = new BufferedReader(new FileReader("br.txt"));
            bw = new BufferedWriter(new FileWriter("br.txt"));
            String line;
            while ((line = br.readLine()) != null) {
                bw.write(line);
                bw.newLine();
                bw.flush();
            }
        } catch (IOException e) {
            throw new RuntimeException(e);
        } finally {
            if (br != null) {
                try {
                    br.close();
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            if (bw != null) {
                try {
                    bw.close();
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
        }
    }
}

JDK7改进方案

在JDK7更新了try catch的新用法，格式为

try(定义流对象){
    可能出现异常的代码
}catch(异常类名 变量名){
    异常的处理代码
}

像是如上操作，不需要使用finally释放资源，会自动释放资源

public class Demo09_1 {
    public static void main(String[] args) {
        try (BufferedWriter bw = new BufferedWriter(new FileWriter("bw.txt"));
             BufferedReader br = new BufferedReader(new FileReader("br.txt"));) {
            String line;
            while ((line = br.readLine()) != null) {
                bw.write(line);
                bw.newLine();
                bw.flush();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

JDK9的改进方案

在这里，JDK9的方案就是把JDK7方案中的try()里面的定义拿到外面去做定义，但会出现方法仍需抛出异常的问题，所以JDK7的方案更靠谱一些