1     public static void main(String[] args) throws Exception { 2         ByteArrayOutputStream bos = new ByteArrayOutputStream();　　　　//字符流 3         OutputStreamWriter osw = new OutputStreamWriter(bos); 4         PrintWriter pw = new PrintWriter(osw); 5         pw.write("helloworld"); 6         pw.flush(); 7         System.out.println(bos.toByteArray().length); 8  9         /*10          * String s = "abcdefasdfasdfasdfasdfasdfasfd";11          * System.out.println("未压缩前:" + s.getBytes().length);12          * 13          * ByteArrayOutputStream baos = new ByteArrayOutputStream(); //14          * 创建一个数组输出流.15          * 16          * GZIPOutputStream gps = new GZIPOutputStream(baos);//17          * 向baos字节数组流写入信息时，进行压缩18          * 19          * gps.write(s.getBytes());20          * 21          * System.out.println("压缩后:" + baos.toByteArray().length);22          * 23          * gps.close();24          * 25          * byte[] b = new byte[1024]; ByteArrayInputStream bis = new26          * ByteArrayInputStream(baos.toByteArray());27          * 28          * GZIPInputStream gis = new GZIPInputStream(bis);29          * 30          * int len = gis.read(b);// 将压缩数组中的信息解压读到b数组中。31          * 32          * System.out.println(new String(b, 0, len));33          * 34          * gis.close();35          */36     }

 

全站压缩过滤器

1 package cn.itcast.filter;  2   3 import java.io.ByteArrayOutputStream;  4 import java.io.IOException;  5 import java.io.OutputStreamWriter;  6 import java.io.PrintWriter;  7 import java.util.zip.GZIPOutputStream;  8   9 import javax.servlet.Filter; 10 import javax.servlet.FilterChain; 11 import javax.servlet.FilterConfig; 12 import javax.servlet.ServletException; 13 import javax.servlet.ServletOutputStream; 14 import javax.servlet.ServletRequest; 15 import javax.servlet.ServletResponse; 16 import javax.servlet.http.HttpServletRequest; 17 import javax.servlet.http.HttpServletRequestWrapper; 18 import javax.servlet.http.HttpServletResponse; 19 import javax.servlet.http.HttpServletResponseWrapper; 20 //全站压缩过滤器 21 public class GzipFilter implements Filter { 22  23     public void destroy() { 24  25     } 26  27     public void doFilter(ServletRequest req, ServletResponse resp, 28             FilterChain chain) throws IOException, ServletException { 29         HttpServletRequest request = (HttpServletRequest)req; 30         HttpServletResponse response = (HttpServletResponse)resp; 31         GzipHttpServletResponse gresponse = new GzipHttpServletResponse(response); 32         chain.doFilter(request, gresponse);//放行 33         //压缩代码写在此处 34         //找一个内存缓冲字节流 35         ByteArrayOutputStream baos = new ByteArrayOutputStream(); 36         //把数据压缩到缓冲字节流流中 37         GZIPOutputStream gout = new GZIPOutputStream(baos); 38         //取出数据：压缩后的 39         byte b[] = gresponse.getOldBytes();//原始字节 40         System.out.println("原有数据大小："+b.length); 41          42         //因为参数是byte b[]数组，所以会调用父类的write(byte[])方法，调用到最后 是write(int b)方法， 43         //而在父类中声明为抽象的，但是MyServletOutputStream实现了，并且在GzipHttpServletResponse对象中 44         //在doFilter()会被调用getOutputStream()函数进行操作进行写入输出流 45         gout.write(b);             46         gout.close();//保证所有的数据都进入内存缓存流 47          48         //取出压缩后的数据 49         b = baos.toByteArray(); 50         System.out.println("压缩后的数据大小："+b.length); 51         //输出前一定要告知客户端压缩方式 52         response.setHeader("Content-Encoding", "gzip"); 53         response.setContentLength(b.length);//告知客户端正文的大小 54         //用服务器的响应对象输出 55         ServletOutputStream out = response.getOutputStream(); 56         out.write(b); 57     } 58  59     public void init(FilterConfig filterConfig) throws ServletException { 60  61     } 62  63 } 64 class GzipHttpServletResponse extends HttpServletResponseWrapper{ 65     private ByteArrayOutputStream baos = new ByteArrayOutputStream();//用于获取压缩前要输出的数据 66     private PrintWriter pw; 67     public GzipHttpServletResponse(HttpServletResponse response){ 68         super(response); 69     } 70     //把原始数据封装到一个缓冲流中 71     @Override 72     public ServletOutputStream getOutputStream() throws IOException { 73         return new MyServletOutputStream(baos); 74     } 75      76     //字符流：把原始数据封装到一个缓冲流中 77     @Override 78     public PrintWriter getWriter() throws IOException {            //改写父方法，自己实现PrintWriter 79         pw = new PrintWriter(new OutputStreamWriter(baos, super.getCharacterEncoding()));//字符流转成字节流编码会丢失 80         return pw; 81     } 82     //返回baos中的缓存数据：原始 83     public byte[] getOldBytes(){ 84         try { 85             if(pw!=null){ 86                 pw.close(); 87             } 88             baos.flush(); 89         } catch (IOException e) { 90             e.printStackTrace(); 91         } 92         return baos.toByteArray(); 93     } 94      95 } 96 class MyServletOutputStream extends ServletOutputStream{ 97     private ByteArrayOutputStream baos; 98     public MyServletOutputStream(ByteArrayOutputStream baos){ 99         this.baos = baos;100     }101     @Override102     public void write(int b) throws IOException {103         baos.write(b);104     }105 }

 如果调用response.getWriter()和response.getOutputStream()会抛异常，所以不能在代码中都调用，以上方法调用的getOutputStream和getWriter自己覆写了，没有调用servlet本身提供的，所以没有报异常。

把字节流和字符流全都放入ByteArrayOutputStream 缓冲中了，一并处理了。