在Java中使用Deflate和Inflate类进行Zlib压缩

Question

我想尝试将java.util.zip中的Deflate和Inflate类用于zlib压缩。

我可以使用Deflate压缩代码，但是在解压缩时却遇到此错误-

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)

到目前为止，这是我的代码-

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");

    }
}

Answer 1

您想在这里做什么？您使用InflaterInputStream来解压缩数据，然后尝试再次将此解压缩后的数据传递给Inflater？使用其中之一，但不能同时使用。

这就是导致您的异常的原因。

除此之外，还有一些小错误，例如bestsss提到的错误：

• 您在循环中完成了压缩-完成后，无法再添加任何数据。
• 您无需检查放气过程会产生多少输出。如果行很长，则可能超过1024个字节。
• 您也可以在不设置长度的情况下将输入设置为充气机a。

我发现了更多：

• 写入后（和从同一文件读取之前），不要关闭FileOutputStream。
• 您readLine()曾经使用过读取一行文本，但随后不再添加换行符，这意味着在解压缩的文件中将不会出现任何换行符。
• 您可以从字节转换为字符串，然后再转换为字节，而无需任何操作。
• 您将创建稍后不使用的变量。

我不会尝试更正您的程序。这是一个简单的示例，它使用DeflaterOutputStream和InflaterInputStream来满足您的要求。（您也可以改用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 http://stackoverflow.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，用缓冲流包装文件流可能很有用。如果这对性能至关重要，请对其进行测量。