Zlib 壓縮在 Java 中使用 Deflate 和 Inflate 類

Question

我想嘗試使用 java.util.zip 中的 Deflate 和 Inflate 類進行 zlib 壓縮。

我可以使用 Deflate 壓縮代碼，但是在解壓縮時，我遇到了這個錯誤 -

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)

到目前為止，這是我的代碼-

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

你想在這里做什么？ 您使用 InflaterInputStream 來解壓縮您的數據，然后您嘗試將這些解壓縮的數據再次傳遞給 Inflater？ 使用其中之一，但不能同時使用。

這就是導致您的異常的原因。

除此之外，還有一些小錯誤，比如 bestsss 提到的這些：

• 您在循環中完成壓縮 - 完成后，無法添加更多數據。
• 您不檢查放氣過程產生了多少 output。 如果你有很長的行，它可能超過 1024 字節。
• 您也將輸入設置為 Inflater 而不設置長度a 。

我發現的更多：

• 寫入后（以及從同一文件讀取之前），您不會關閉 FileOutputStream。
• 您使用readLine()讀取一行文本，但隨后您不再添加換行符，這意味着在您的解壓縮文件中不會有任何換行符。
• 您無需任何需要即可從字節轉換為字符串並再次轉換為字節。
• 您創建以后不使用的變量。

我不會試圖糾正你的程序。 這是一個簡單的，它使用 DeflaterOutputStream 和 InflaterInputStream 完成我認為你想要的。 （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"));
    }
}

為了提高效率，用緩沖流包裝文件流可能很有用。 如果這對性能至關重要，請對其進行測量。

Answer 2

Paŭlo Ebermann的代碼可以通過使用try-with-resources進一步改進：

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

public class ZLibCompression
{
    public static void compress(File raw, File compressed) throws IOException
    {
        try (InputStream inputStream = new FileInputStream(raw);
             OutputStream outputStream = new DeflaterOutputStream(new FileOutputStream(compressed)))
        {
            copy(inputStream, outputStream);
        }
    }

    public static void decompress(File compressed, File raw)
            throws IOException
    {
        try (InputStream inputStream = new InflaterInputStream(new FileInputStream(compressed));
             OutputStream outputStream = new FileOutputStream(raw))
        {
            copy(inputStream, outputStream);
        }
    }

    public static String decompress(File compressed) throws IOException
    {
        try (InputStream inputStream = new InflaterInputStream(new FileInputStream(compressed)))
        {
            return toString(inputStream);
        }
    }

    private static String toString(InputStream inputStream)
    {
        try (Scanner scanner = new Scanner(inputStream).useDelimiter("\\A"))
        {
            return scanner.hasNext() ? scanner.next() : "";
        }
    }

    private static void copy(InputStream inputStream, OutputStream outputStream)
            throws IOException
    {
        byte[] buffer = new byte[1000];
        int length;

        while ((length = inputStream.read(buffer)) > 0)
        {
            outputStream.write(buffer, 0, length);
        }
    }
}