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servlet中使用HttpServletResponseWrapper截获返回的页面内容

2013-05-01 22:25 639 查看

知名的页面装饰框架sitemesh，就是利用filter过滤器先截获返回给客户端的页面，然后分析html代码并最终装饰页面效果后返回给客户端。我这里也先简单的说下如何来自己编程实现，然后说一个我遇到的问题，应该也是大家会遇到但很难找到原因的问题。

要截获页面返回的内容，整体的思路是先把原始返回的页面内容写入到一个字符Writer，然后再组装成字符串并进行分析，最后再返回给客户端。代码如下：package org.sim.response;

import java.io.CharArrayWriter;
import java.io.PrintWriter;

import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpServletResponseWrapper;

public class ResponseWrapper extends HttpServletResponseWrapper {

private PrintWriter cachedWriter;
private CharArrayWriter bufferedWriter;

public ResponseWrapper(HttpServletResponse response) {
super(response);
bufferedWriter = new CharArrayWriter();
cachedWriter = new PrintWriter(bufferedWriter);
}

@Override
public PrintWriter getWriter() {
return cachedWriter;
}

public String getResult() {
return bufferedWriter.toString();
}
}

然后再写一个过滤器来截获内容并处理：
package org.sim.filter;

import java.io.IOException;
import java.io.PrintWriter;

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.HttpServletResponse;

import org.sim.response.ResponseWrapper;

public class MyServletFilter implements Filter {

@Override
public void destroy() {
// TODO Auto-generated method stub

}

@Override
public void doFilter(ServletRequest req, ServletResponse resp,
FilterChain chain) throws IOException, ServletException {
ResponseWrapper wrapper = new ResponseWrapper((HttpServletResponse)resp);
chain.doFilter(req, wrapper);

String result = wrapper.getResult();
System.out.println(result);
result = result.replace("大头", "大脑袋");
PrintWriter out = resp.getWriter();

System.out.println("++++++++++++++++++++++++++");
System.out.println(out);

out.write(result);
out.flush();
out.close();
}

@Override
public void init(FilterConfig arg0) throws ServletException {
// TODO Auto-generated method stub

}

}

然后将该servlet配置在web.xml文件中，如下：
<filter>
<filter-name>myWrapper</filter-name>
<filter-class>org.sim.filter.MyServletFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>myWrapper</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>

jsp:
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>

大头的jsp
</body>
</html>

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标签： servlet

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