javaweb过滤器修改Response的返回值
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以前就听说javaweb中的过滤器可以修改请求过来和响应回去的数据,请求过来的数据修改比较简单,在此主要讨论的是响应回去的数据,咱们如何修改?
tomcat源码中提供了一个类HttpServletResponseWrapper,该类实际上实现了HttpServletResponse接口,也就是过滤器中直接封装该类的子类就可以调用,以下是该类部分源码。
public class HttpServletResponseWrapper extends ServletResponseWrapper implements HttpServletResponse { public HttpServletResponseWrapper(HttpServletResponse response) { super(response); } private HttpServletResponse _getHttpServletResponse() { return (HttpServletResponse)super.getResponse(); }
还记得输出时是通过response.getOutputStream()或者resp.getWriter()获取的输出流,然后将需要返回的数据写入数据流中;我们可以拿到这两个输出流,但是这两个流都是包装流,数据没办法直接从这两个输出流中读取出来,这该如何解决?那我们能不能自己封装这样的一个接口呢,看下面的代码:
package com.asiainfo.wrapper; import java.io.ByteArrayOutputStream; import java.io.IOException; import java.io.OutputStream; import java.io.PrintWriter; import javax.servlet.ServletOutputStream; import javax.servlet.http.HttpServletResponse; import javax.servlet.http.HttpServletResponseWrapper; /** * 返回值输出代理类 * @author Administrator * */ public class ResponseWrapper extends HttpServletResponseWrapper { // 真正缓存数据的流private ByteArrayOutputStream buffer = null; private ServletOutputStream out = null; private PrintWriter writer = null; public ResponseWrapper(HttpServletResponse response) { super(response); // TODO Auto-generated constructor stub buffer = new ByteArrayOutputStream(); out = new WrapperOutputStream(buffer); writer = new PrintWriter(buffer); } /** * 当获取字节输出流时,实际获取的是我们自己包装的字节输出流 */public ServletOutputStream getOutputStream() { return out; } /** * 当获取字符输出流时,实际获取的是我们自己包装的字符输出流 */public PrintWriter getWriter() { return writer; } publicvoid flushBuffer() throws IOException { if (out != null) { out.flush(); } if (writer != null) { writer.flush(); } } publicbyte[] getResponseData() throws IOException { flushBuffer(); return buffer.toByteArray(); } public String getContent() throws IOException { flushBuffer(); return buffer.toString(); } } class WrapperOutputStream extends ServletOutputStream { private OutputStream out; public WrapperOutputStream(OutputStream out) { super(); this.out = out; } @Override publicvoid write(int b) throws IOException { // TODO Auto-generated method stub out.write(b); } }
写一个servlet处理调用请求
package com.asiainfo.servlet; import java.io.IOException; import javax.servlet.ServletException; import javax.servlet.ServletOutputStream; import javax.servlet.annotation.WebServlet; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; @WebServlet("/demo") publicclass FrontServlet extends HttpServlet { @Override protectedvoid service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { // TODO Auto-generated method stub ServletOutputStream outputStream = resp.getOutputStream(); resp.setContentType("application/json;charset=UTF-8"); String content = "{\"a\":\"前置servlet\"}"; outputStream.write("{\"a\":\"前置servlet\"}".getBytes("utf-8")); System.out.println("servlet中写入的内容:"+content); outputStream.flush(); outputStream.close(); } }
下面是写两个过滤器,DemoFilter2先对servlet中相应数据做修改,然后可以在DemoFilter1中查看修改后的内容,代码如下:
package com.asiainfo; import java.io.IOException; 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.annotation.WebFilter; import javax.servlet.http.HttpServletResponse; import com.asiainfo.wrapper.ResponseWrapper; @WebFilter("/*") publicclass DemoFilter2 implements Filter { @Override publicvoid destroy() { // TODO Auto-generated method stub } @Override publicvoid doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain chain) throws IOException, ServletException { ResponseWrapper responseWrapper = new ResponseWrapper((HttpServletResponse) servletResponse); chain.doFilter(servletRequest, responseWrapper); byte[] content = responseWrapper.getResponseData(); String str = ""; if (content != null && !"".equals(content)) { // 这里可以对相应数据做修改,修改后的内容 str = "{\"a\":\"前置servlet\",\"b\":\"新增内容\"}"; System.out.println("第二个过滤器修改后的内容:" + str); HttpServletResponse response = (HttpServletResponse) servletResponse; // 注意:这里的response还要传原来的,不然内容无法输出页面 writeResponse(response, 200, str); } } publicstaticvoid writeResponse(HttpServletResponse response, int status, String json) { try { response.setContentType("application/json;charset=UTF-8"); response.setStatus(status); response.getWriter().write(json); } catch (IOException e) { e.printStackTrace(); } } @Override publicvoid init(FilterConfig arg0) throws ServletException { // TODO Auto-generated method stub } } package com.asiainfo; import java.io.IOException; 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.annotation.WebFilter; import javax.servlet.http.HttpServletResponse; import com.asiainfo.wrapper.ResponseWrapper; @WebFilter("/*") publicclass DemoFilter1 implements Filter { @Override publicvoid init(FilterConfig filterconfig) throws ServletException { // TODO Auto-generated method stub } @Override publicvoid doFilter(ServletRequest servletrequest, ServletResponse servletresponse, FilterChain filterchain) throws IOException, ServletException { // TODO Auto-generated method stub ResponseWrapper responseWrapper = new ResponseWrapper((HttpServletResponse) servletresponse); filterchain.doFilter(servletrequest, responseWrapper); String content = responseWrapper.getContent(); if (content != null) { System.out.println("第一个过滤器读取到的内容:"+content); } HttpServletResponse response = (HttpServletResponse) servletresponse; writeResponse(response, 200, content); } publicstaticvoid writeResponse(HttpServletResponse response, int status, String json) { try { response.setContentType("application/json;charset=UTF-8"); response.setStatus(status); response.getWriter().write(json); } catch (IOException e) { e.printStackTrace(); } } @Override publicvoid destroy() { // TODO Auto-generated method stub } }
将上面的web工程部署到tomcat中启动,浏览器中调用地址:http://localhost:8080/DemoFilter/demo
结果显示如下:
控制台结果:
原文:https://www.cnblogs.com/wudy945/p/12971574.html
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