Java文件压缩

从接触计算机开始，便知道了压缩文件的存在，刚开始不解（本来我一次就可以打开文件，现在却多了一步，乃是解压。。。)到了后来，我才慢慢明白压缩的重要性，除了节省空间，还节省了时间。有时候压缩文件的结果会让你吃惊，大概在原文件的50%左右，这样在网络端传输的时间将缩短一半。由此可见，它是有多么的重要。

单个文件压缩

首选GZIP

public static void compress(File source, File gzip) {
    if(source == null || gzip == null) 
        throw new NullPointerException();
    BufferedReader reader = null;
    BufferedOutputStream bos = null;
    try {
        //读取文本文件可以字符流读取
        reader = new BufferedReader(new FileReader(source));
        //对于GZIP输出流，只能使用字节流
        bos = new BufferedOutputStream(new GZIPOutputStream(new FileOutputStream(gzip)));
        String data;
        while((data = reader.readLine()) != null) {
            bos.write(data.getBytes());
        }
    }  catch (IOException e) {
        throw new RuntimeException(e);
    }  finally {
        try {
            if(reader != null)
                reader.close();
            if(bos != null) 
                bos.close();
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
        
    }
}

多文件压缩

public static void compressMore(File[] files, File outFile) {
    if(files == null || outFile == null) 
        throw new NullPointerException();
    ZipOutputStream zipStream = null;
    try {
        //用校验流确保输出数据的完整性
        CheckedOutputStream cos = new CheckedOutputStream(new FileOutputStream(outFile), new Adler32());
        //用缓冲字节输出流进行包装
        zipStream = new ZipOutputStream(new BufferedOutputStream(cos));
        for (File file : files) {
            if(file != null) {
                BufferedInputStream in = new BufferedInputStream(new FileInputStream(file));
                try {
                    //添加实体到流中，实际上只需要指定文件名称
                    zipStream.putNextEntry(new ZipEntry(file.getName()));
                    int c;
                    while((c = in.read()) != -1)
                        zipStream.write(c);
                } catch (IOException e) {
                    throw new RuntimeException(e);
                } finally {
                    in.close();
                }   
            }
        }
    } catch (IOException e) {
        throw new RuntimeException(e);
    } finally {
        try{
            if(zipStream != null)
                zipStream.close();
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }
}