利用Filter压缩HTTP响应
/*
* Copyright 2004 The Apache Software Foundation
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may oBTain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either eXPress or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
import Java.io.IOException;
import java.util.Enumeration;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* Implementation of <code>javax.servlet.Filter</code> used to compress
* the ServletResponse if it is bigger than a threshold.
*
* @author Amy Roh
* @author Dmitri Valdin
* @version $Revision: 1.2 $, $Date: 2004/03/18 16:40:33 $
*/
public class CompressionFilter implements Filter{
/**
* The filter configuration object we are associated with. If this value
* is null, this filter instance is not currently configured.
*/
private FilterConfig config = null;
/**
* Minimal reasonable threshold
*/
private int minThreshold = 128;
/**
* The threshold number to compress
*/
protected int compressionThreshold;
/**
* Debug level for this filter
*/
private int debug = 0;
/**
* Place this filter into service.
*
* @param filterConfig The filter configuration object
*/
public void init(FilterConfig filterConfig) {
config = filterConfig;
if (filterConfig != null) {
String value = filterConfig.getInitParameter("debug");
if (value!=null) {
debug = Integer.parseInt(value);
} else {
debug = 0;
}
String str = filterConfig.getInitParameter("compressionThreshold");
if (str!=null) {
compressionThreshold = Integer.parseInt(str);
if (compressionThreshold != 0 && compressionThreshold < minThreshold) { if (debug > 0) {
System.out.println("compressionThreshold should be either 0 - no compression or >= " + minThreshold);
System.out.println("compressionThreshold set to " + minThreshold);
}
compressionThreshold = minThreshold;
}
} else {
compressionThreshold = 0;
}
} else {
compressionThreshold = 0;
}
}
/**
* Take this filter out of service.
*/
public void destroy() {
this.config = null;
}
/**
* The <code>doFilter</code> method of the Filter is called by the container
* each time a request/response pair is passed through the chain due
* to a client request for a resource at the end of the chain.
* The FilterChain passed into this method allows the Filter to pass on the
* request and response to the next entity in the chain.<p>
* This method first examines the request to check whether the client support
* compression. <br>
* It simply just pass the request and response if there is no support for
* compression.<br>
* If the compression support is available, it creates a
* CompressionServletResponseWrapper object which compresses the content and
* modifies the header if the content length is big enough.
* It then invokes the next entity in the chain using the FilterChain object
* (<code>chain.doFilter()</code>), <br>
**/
public void doFilter ( ServletRequest request, ServletResponse response,
FilterChain chain ) throws IOException, ServletException {
if (debug > 0) {
System.out.println("@doFilter");
}
if (compressionThreshold == 0) {
if (debug > 0) {
System.out.println("doFilter gets called, but compressionTreshold is set to 0 - no compression");
}
chain.doFilter(request, response);
return;
}
boolean supportCompression = false;
if (request instanceof HttpServletRequest) {
if (debug > 1) {
System.out.println("requestURI = " + ((HttpServletRequest)request).getRequestURI());
}
// Are we allowed to compress ?
String s = (String) ((HttpServletRequest)request).getParameter("gzip");
if ("false".equals(s)) {
if (debug > 0) {
System.out.println("got parameter gzip=false --> don't compress, just chain filter");
}
chain.doFilter(request, response);
return;
}
Enumeration e =
((HttpServletRequest)request).getHeaders("Accept-Encoding");
while (e.hasMoreElements()) {
String name = (String)e.nextElement();
if (name.indexOf("gzip") != -1) {
if (debug > 0) {
System.out.println("supports compression");
}
supportCompression = true;
} else {
if (debug > 0) {
System.out.println("no support for compresion");
}
}
}
}
if (!supportCompression) {
if (debug > 0) {
System.out.println("doFilter gets called wo compression");
}
chain.doFilter(request, response);
return;
} else {
if (response instanceof HttpServletResponse) {
CompressionServletResponseWrapper wrappedResponse =
new CompressionServletResponseWrapper((HttpServletResponse)response);
wrappedResponse.setDebugLevel(debug);
wrappedResponse.setCompressionThreshold(compressionThreshold);
if (debug > 0) {
System.out.println("doFilter gets called with compression");
}
try {
chain.doFilter(request, wrappedResponse);
} finally {
wrappedResponse.finishResponse();
}
return;
}
}
}
/**
* Set filter config
* This function is equivalent to init. Required by Weblogic 6.1
*
* @param filterConfig The filter configuration object
*/
public void setFilterConfig(FilterConfig filterConfig) {
init(filterConfig);
}
/**
* Return filter config
* Required by Weblogic 6.1
*/
public FilterConfig getFilterConfig() {
return config;
}
}
/*
* Copyright 2004 The Apache Software Foundation
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Enumeration;
import javax.servlet.*;
import javax.servlet.http.*;
/**
* Very Simple test servlet to test compression filter
* @author Amy Roh
* @version $Revision: 1.2 $, $Date: 2004/03/18 16:40:33 $
*/
public class CompressionFilterTestServlet extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
ServletOutputStream out = response.getOutputStream();
response.setContentType("text/plain");
Enumeration e = ((HttpServletRequest)request).getHeaders("Accept-Encoding");
while (e.hasMoreElements()) {
String name = (String)e.nextElement();
out.println(name);
if (name.indexOf("gzip") != -1) {
out.println("gzip supported -- able to compress");
}
else {
out.println("gzip not supported");
}
}
out.println("Compression Filter Test Servlet");
out.close();
}
}
（出处：http://www.knowsky.com）
