public static byte[] compress(String str, String encoding) {
    if (str == null || str.length() == 0) {
      return null;
    }
    ByteArrayOutputStream out = new ByteArrayOutputStream();
    GZIPOutputStream gzip;
    try {
      gzip = new GZIPOutputStream(out);
      gzip.write(str.getBytes(encoding));
      gzip.close();
    } catch ( Exception e) {
      e.printStackTrace();
    }
    return out.toByteArray();
  }

public static byte[] uncompress(byte[] bytes) {
    if (bytes == null || bytes.length == 0) {
      return null;
    }
    ByteArrayOutputStream out = new ByteArrayOutputStream();
    ByteArrayInputStream in = new ByteArrayInputStream(bytes);
    try {
      GZIPInputStream ungzip = new GZIPInputStream(in);
      byte[] buffer = new byte[256];
      int n;
      while ((n = ungzip.read(buffer)) >= 0) {
        out.write(buffer, 0, n);
      }
    } catch (Exception e) {
      e.printStackTrace();
    }
    return out.toByteArray();
  }

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.util.zip.GZIPInputStream;
import java.util.zip.GZIPOutputStream;

public class GZIPUtils {
  public static final String GZIP_ENCODE_UTF_8 = "UTF-8"; 
  public static final String GZIP_ENCODE_ISO_8859_1 = "ISO-8859-1";

  
  public static byte[] compress(String str, String encoding) {
    if (str == null || str.length() == 0) {
      return null;
    }
    ByteArrayOutputStream out = new ByteArrayOutputStream();
    GZIPOutputStream gzip;
    try {
      gzip = new GZIPOutputStream(out);
      gzip.write(str.getBytes(encoding));
      gzip.close();
    } catch ( Exception e) {
      e.printStackTrace();
    }
    return out.toByteArray();
  }
  
  public static byte[] compress(String str) throws IOException { 
    return compress(str, GZIP_ENCODE_UTF_8); 
  }
  
  public static byte[] uncompress(byte[] bytes) {
    if (bytes == null || bytes.length == 0) {
      return null;
    }
    ByteArrayOutputStream out = new ByteArrayOutputStream();
    ByteArrayInputStream in = new ByteArrayInputStream(bytes);
    try {
      GZIPInputStream ungzip = new GZIPInputStream(in);
      byte[] buffer = new byte[256];
      int n;
      while ((n = ungzip.read(buffer)) >= 0) {
        out.write(buffer, 0, n);
      }
    } catch (Exception e) {
      e.printStackTrace();
    }
    return out.toByteArray();
  }
  
  public static String uncompressToString(byte[] bytes, String encoding) { 
    if (bytes == null || bytes.length == 0) { 
      return null; 
    } 
    ByteArrayOutputStream out = new ByteArrayOutputStream(); 
    ByteArrayInputStream in = new ByteArrayInputStream(bytes); 
    try {
      GZIPInputStream ungzip = new GZIPInputStream(in); 
      byte[] buffer = new byte[256]; 
      int n; 
      while ((n = ungzip.read(buffer)) >= 0) { 
        out.write(buffer, 0, n); 
      } 
      return out.toString(encoding);
    } catch (Exception e) {
      e.printStackTrace();
    }
    return null;
  }
  
  public static String uncompressToString(byte[] bytes) { 
    return uncompressToString(bytes, GZIP_ENCODE_UTF_8); 
  } 
  
  public static void main(String[] args) throws IOException {
    String s = "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa";
    System.out.println("字符串長(zhǎng)度："+s.length());
    System.out.println("壓縮后：："+compress(s).length);
    System.out.println("解壓后："+uncompress(compress(s)).length);
    System.out.println("解壓字符串后：："+uncompressToString(compress(s)).length());
  }
}