我想尝试使用java.util.zip中的Deflate和Inflate类进行zlib压缩.

我能够使用Deflate压缩代码,但在解压缩时,我遇到了这个错误 –

Exception in thread "main" java.util.zip.DataFormatException: unknown compression method
    at java.util.zip.Inflater.inflateBytes(Native Method)
    at java.util.zip.Inflater.inflate(Inflater.java:238)
    at java.util.zip.Inflater.inflate(Inflater.java:256)
    at zlibCompression.main(zlibCompression.java:53)

这是我目前的代码 –

import java.util.zip.*;
import java.io.*;

public class zlibCompression {

    /**
     * @param args
     */
    public static void main(String[] args) throws IOException, DataFormatException {
        // TODO Auto-generated method stub

        String fname = "book1";
        FileReader infile = new FileReader(fname);
        BufferedReader in = new BufferedReader(infile);

        FileOutputStream out = new FileOutputStream("book1out.dfl");
        //BufferedInputStream in = new BufferedInputStream(new FileInputStream(filename));

        Deflater compress = new Deflater();
        Inflater decompress = new Inflater();

        String readFile = in.readLine();
        byte[] bx = readFile.getBytes();

        while(readFile!=null){
            byte[] input = readFile.getBytes();
            byte[] compressedData = new byte[1024];
            compress.setInput(input);
            compress.finish();
            int compressLength = compress.deflate(compressedData, 0, compressedData.length);
            //System.out.println(compressedData);
            out.write(compressedData, 0, compressLength);
            readFile = in.readLine();
        }

        File abc = new File("book1out.dfl");
        InputStream is = new FileInputStream("book1out.dfl");

        InflaterInputStream infl = new InflaterInputStream(new FileInputStream("book1out.dfl"), new Inflater());
        FileOutputStream outFile = new FileOutputStream("decompressed.txt");

        byte[] b = new byte[1024];
        while(true){

            int a = infl.read(b,0,1024);
            if(a==0)
                break;

            decompress.setInput(b);
            byte[] fresult = new byte[1024];
            //decompress.in
            int resLength = decompress.inflate(fresult);
            //outFile.write(b,0,1);
            //String outt = new String(fresult, 0, resLength);
            //System.out.println(outt);
        }

        System.out.println("complete");

    }
}

解决方法:

你想在这做什么？您使用InflaterInputStream解压缩数据,然后尝试将此解压缩数据再次传递给Inflater？使用其中任何一个,但不能同时使用两个.

这就是导致你的例外的原因.

除此之外,还有一些小错误,比如bestsss提到的这些错误：

>您在循环中完成压缩 – 完成后,不能再添加数据.
>您不检查放气过程产生的输出量.如果您有长行,则可能超过1024个字节.
>您也可以在不设置长度a的情况下将输入设置到Inflater.

我发现了一些：

>写入后(以及从同一文件读取之前)不要关闭FileOutputStream.
>您使用readLine()读取一行文本,但之后不再添加换行符,这意味着在解压缩文件中不会出现任何换行符.
>无需任何需要,您可以从字节转换为字符串并再次转换为字节.
>您创建以后不使用的变量.

我不会试图纠正你的程序.这是一个使用DeflaterOutputStream和InflaterInputStream完成我认为你想要的东西. (您也可以使用JZlib的ZInputStream和ZOutputStream.)

import java.util.zip.*;
import java.io.*;

/**
 * Example program to demonstrate how to use zlib compression with
 * Java.
 * Inspired by https://*.com/q/6173920/600500.
 */
public class ZlibCompression {

    /**
     * Compresses a file with zlib compression.
     */
    public static void compressFile(File raw, File compressed)
        throws IOException
    {
        InputStream in = new FileInputStream(raw);
        OutputStream out =
            new DeflaterOutputStream(new FileOutputStream(compressed));
        shovelInToOut(in, out);
        in.close();
        out.close();
    }

    /**
     * Decompresses a zlib compressed file.
     */
    public static void decompressFile(File compressed, File raw)
        throws IOException
    {
        InputStream in =
            new InflaterInputStream(new FileInputStream(compressed));
        OutputStream out = new FileOutputStream(raw);
        shovelInToOut(in, out);
        in.close();
        out.close();
    }

    /**
     * Shovels all data from an input stream to an output stream.
     */
    private static void shovelInToOut(InputStream in, OutputStream out)
        throws IOException
    {
        byte[] buffer = new byte[1000];
        int len;
        while((len = in.read(buffer)) > 0) {
            out.write(buffer, 0, len);
        }
    }


    /**
     * Main method to test it all.
     */
    public static void main(String[] args) throws IOException, DataFormatException {
        File compressed = new File("book1out.dfl");
        compressFile(new File("book1"), compressed);
        decompressFile(compressed, new File("decompressed.txt"));
    }
}

为了提高效率,使用缓冲流包装文件流可能很有用.如果这是性能关键,请测量它.