Gzip 服務端壓縮數據

Gzip 服務端壓縮數據，提升傳輸速率。

首先寫一個過濾器

public class GzipValidator implements Filter{

@Override

public void destroy() {


}

@Override

public void doFilter(ServletRequest arg0, ServletResponse arg1,

FilterChain filterChain) throws IOException, ServletException {

HttpServletRequest request=  (HttpServletRequest) arg0 ;

HttpServletResponse response = (HttpServletResponse) arg1;

CachedResponseWrapper responseWrapper = null ;

responseWrapper = new CachedResponseWrapper(response);

filterChain.doFilter(request, responseWrapper);

byte[] responseData = responseWrapper.getResponseData();

System.out.println(responseData.length);

//壓縮數據

responseData=compress(request, responseWrapper, responseData);

System.out.println(responseData.length);

//發送數據

response.setContentLength(responseData.length);

response.setHeader("Content-Encoding", "gzip");

ServletOutputStream output = response.getOutputStream();

//由於是包裝事後的因此要從新輸出

output.write(responseData);

output.flush();

output.close();

}

public byte[] compress(HttpServletRequest request,

HttpServletResponse response, byte[] responseData){


String acceptEncoding = request.getHeader("Accept-Encoding");

if ( acceptEncoding == null

||!acceptEncoding.contains("gzip")) {

return responseData;

}

response.setHeader("Content-Encoding", "gzip");

return GzipUtil.gzip(responseData);

}

@Override

public void init(FilterConfig arg0) throws ServletException {

}

}

GzipUtil 類

public class GzipUtil {

public static byte[] gzip(byte[] data){

ByteArrayOutputStream byteOutput=new ByteArrayOutputStream(10240);

GZIPOutputStream output =null;

try {

output = new GZIPOutputStream(byteOutput);

output.write(data);

} catch (IOException e) {

throw new RuntimeException("Gzip failed.", e);

} finally {

if (output != null) {

try {

output.close();

} catch (IOException e) {

}

}

}

return byteOutput.toByteArray();//將字節流轉換爲byte數組

}

}

CachedResponseWrapper類

public class CachedResponseWrapper extends HttpServletResponseWrapper{

/** 

     * Indicate that getOutputStream() or getWriter() is not called yet. 

     */  

    public static final int OUTPUT_NONE = 0;  

  

    /** 

     * Indicate that getWriter() is already called. 

     */  

    public static final int OUTPUT_WRITER = 1;  

    /** 

     * Indicate that getOutputStream() is already called. 

     */  

    public static final int OUTPUT_STREAM = 2;  

    private int outputType = OUTPUT_NONE;  

    private int status = SC_OK;  

    private ServletOutputStream output = null;  

    private PrintWriter writer = null;  

    private ByteArrayOutputStream buffer = null;  

    public CachedResponseWrapper(HttpServletResponse resp) throws IOException {  

        super(resp);  

        buffer = new ByteArrayOutputStream();  

    }  

    public int getStatus() {  

        return status;  

    }  

    public void setStatus(int status) {  

        this.status = status;  

    }  

    public void setStatus(int status, String string) {  

        super.setStatus(status, string);  

        this.status = status;  

    }  

    public void sendError(int status, String string) throws IOException {  

        super.sendError(status, string);  

        this.status = status;  

    }  

    public void sendError(int status) throws IOException {  

        super.sendError(status);  

        this.status = status;  

    }  

    public void sendRedirect(String location) throws IOException {  

        super.sendRedirect(location);  

        this.status = SC_MOVED_TEMPORARILY;  

    }  

    public PrintWriter getWriter() throws IOException {  

        if (outputType == OUTPUT_STREAM)  

            throw new IllegalStateException();  

        else if (outputType == OUTPUT_WRITER)  

            return writer;  

        else {  

            outputType = OUTPUT_WRITER;  

            writer = new PrintWriter(new OutputStreamWriter(buffer,  

                    getCharacterEncoding()));  

            return writer;  

        }  

    }  

    public ServletOutputStream getOutputStream() throws IOException {  

        if (outputType == OUTPUT_WRITER)  

            throw new IllegalStateException();  

        else if (outputType == OUTPUT_STREAM)  

            return output;  

        else {  

            outputType = OUTPUT_STREAM;  

            output = new WrappedOutputStream(buffer);  

            return output;  

        }  

    }  

    public void flushBuffer() throws IOException {  

        if (outputType == OUTPUT_WRITER)  

            writer.flush();  

        if (outputType == OUTPUT_STREAM)  

            output.flush();  

    }  

    public void reset() {  

        outputType = OUTPUT_NONE;  

        buffer.reset();  

    }  

    /** 

     * Call this method to get cached response data. 

     *  

     * @return byte array buffer. 

     * @throws IOException 

     */  

    public byte[] getResponseData() throws IOException {  

        flushBuffer();  

        return buffer.toByteArray();  

    }  

    /** 

     * This class is used to wrap a ServletOutputStream and store output stream 

     * in byte[] buffer. 

     */  

    class WrappedOutputStream extends ServletOutputStream {  

        private ByteArrayOutputStream buffer;  

        public WrappedOutputStream(ByteArrayOutputStream buffer) {  

            this.buffer = buffer;  

        }  

        public void write(int b) throws IOException {  

            buffer.write(b);  

        }  

        public byte[] toByteArray() {  

            return buffer.toByteArray();  

        }  

    }  

}

 

遇到的問題：發送數據的時候先設置相應數據的長度再得到包裝以後的輸出流。