java解压zip文件示例

若是使用java自带的压缩工具包来实现解压缩文件到指定文件夹的功能，因为jdk提供的zip只能按utf-8格式处理，而windows系统中文件名是以gbk方式编码的，所以如果是解压一个包含中文文件名的zip包，会报非法参数异常，所以要实现解压缩，就得对deflateroutputstream.java、inflaterinputstream.java、zipconstants.java、zipentry.java、zipinputstream.java以及zipoutputstream.java这些相关的类进行修改，过程如下：
因为从 j2se 1.4 开始，java 编译器不再支持 import 进未命包名的类、接口，所以在创建的java项目中，一定要新建一个自己定义的包，包命名的格式一般为学校域名的逆序+自己的网名，比如cn.edu.xidian.crytoll。
在包内新建deflateroutputstream类，代码如下：

deflateroutputstream.java:

package cn.edu.xdian.crytoll;

import java.io.filteroutputstream;
import java.io.ioexception;
import java.io.outputstream;
import java.util.zip.deflater;

/**
 * this class implements an output stream filter for compressing data in
 * the "deflate" compression format. it is also used as the basis for other
 * types of compression filters, such as gzipoutputstream.
 *
 * @see     deflater
 * @version     1.36, 03/13/06
 * @author  david connelly
 */
public
class deflateroutputstream extends filteroutputstream {
    /**
     * compressor for this stream.
     */
    protected deflater def;

    /**
     * output buffer for writing compressed data.
     */
    protected byte[] buf;

    /**
     * indicates that the stream has been closed.
     */

    private boolean closed = false;

    /**
     * creates a new output stream with the specified compressor and
     * buffer size.
     * @param out the output stream
     * @param def the compressor ("deflater")
     * @param size the output buffer size
     * @exception illegalargumentexception if size is <= 0
     */
    public deflateroutputstream(outputstream out, deflater def, int size) {
        super(out);
        if (out == null || def == null) {
            throw new nullpointerexception();
        } else if (size <= 0) {
            throw new illegalargumentexception("buffer size <= 0");
        }
        this.def = def;
        buf = new byte[size];
    }

    /**
     * creates a new output stream with the specified compressor and
     * a default buffer size.
     * @param out the output stream
     * @param def the compressor ("deflater")
     */
    public deflateroutputstream(outputstream out, deflater def) {
    this(out, def, 512);
    }

    boolean usesdefaultdeflater = false;

    /**
     * creates a new output stream with a default compressor and buffer size.
     * @param out the output stream
     */
    public deflateroutputstream(outputstream out) {
    this(out, new deflater());
        usesdefaultdeflater = true;
    }

    /**
     * writes a byte to the compressed output stream. this method will
     * block until the byte can be written.
     * @param b the byte to be written
     * @exception ioexception if an i/o error has occurred
     */
    public void write(int b) throws ioexception {
        byte[] buf = new byte[1];
    buf[0] = (byte)(b & 0xff);
    write(buf, 0, 1);
    }

    /**
     * writes an array of bytes to the compressed output stream. this
     * method will block until all the bytes are written.
     * @param b the data to be written
     * @param off the start offset of the data
     * @param len the length of the data
     * @exception ioexception if an i/o error has occurred
     */
    public void write(byte[] b, int off, int len) throws ioexception {
    if (def.finished()) {
        throw new ioexception("write beyond end of stream");
    }
        if ((off | len | (off + len) | (b.length - (off + len))) < 0) {
        throw new indexoutofboundsexception();
    } else if (len == 0) {
        return;
    }
    if (!def.finished()) {
            // deflate no more than stride bytes at a time.  this avoids
            // excess copying in deflatebytes (see deflater.c)
            int stride = buf.length;
            for (int i = 0; i < len; i+= stride) {
                def.setinput(b, off + i, math.min(stride, len - i));
                while (!def.needsinput()) {
                    deflate();
                }
            }
    }
    }

    /**
     * finishes writing compressed data to the output stream without closing
     * the underlying stream. use this method when applying multiple filters
     * in succession to the same output stream.
     * @exception ioexception if an i/o error has occurred
     */
    public void finish() throws ioexception {
    if (!def.finished()) {
        def.finish();
        while (!def.finished()) {
        deflate();
        }
    }
    }

    /**
     * writes remaining compressed data to the output stream and closes the
     * underlying stream.
     * @exception ioexception if an i/o error has occurred
     */
    public void close() throws ioexception {
        if (!closed) {
            finish();
            if (usesdefaultdeflater)
                def.end();
            out.close();
            closed = true;
        }
    }

    /**
     * writes next block of compressed data to the output stream.
     * @throws ioexception if an i/o error has occurred
     */
    protected void deflate() throws ioexception {
    int len = def.deflate(buf, 0, buf.length);
    if (len > 0) {
        out.write(buf, 0, len);
    }
    }
}