Java filter中的chain.doFilter使用詳解
filter中的chain.doFilter使用
chain.doFilter作用
1.一般filter都是一個鏈,web.xml 裡面配置瞭幾個就有幾個。一個一個的連在一起
request -> filter1 -> filter2 ->filter3 -> …. -> request resource.
2.chain.doFilter將請求轉發給過濾器鏈下一個filter , 如果沒有filter那就是你請求的資源
舉例說明
1.input.jsp 是用來提交輸入的 : 當提交後,過濾器檢測姓名和年齡 .
2.如果正常的話會提交給output.jsp 如果不正常提交給erroroutput.jsp.
3.在此 , 同時也有一個過濾器,防止亂碼問題存在 , 該過濾器檢測一個頁面是否設置瞭字符編碼,如果沒有則進行設置。
1.input.jsp
<form action="output.jsp" name="form" method="post"> <table> <tr> <td>name</td> <td><input type="text" name="name" /></td> </tr> <tr> <td>age</td> <td><input type="text" name="age"/></td> </tr> <tr> <td><input type="submit" name="ok" value="ok"/></td> </tr> </table> </form>
2.web.xml
<filter> <description></description> <display-name>encodefilter</display-name> <filter-name>encodefilter</filter-name> <filter-class>servletbean.encodefilter</filter-class> <init-param> <param-name>encoding</param-name> <param-value>GB2312</param-value> </init-param> </filter> <filter-mapping> <filter-name>encodefilter</filter-name> <url-pattern>/*</url-pattern> </filter-mapping> <filter> <description></description> <display-name>myfilter</display-name> <filter-name>myfilter</filter-name> <filter-class>servletbean.myfilter</filter-class> </filter> <filter-mapping> <filter-name>myfilter</filter-name> <url-pattern>/output.jsp</url-pattern> </filter-mapping>
3.encodefilter.java
package servletbean; public class encodefilter implements Filter { public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { if(request.getCharacterEncoding()==null) { System.out.println(encoding); request.setCharacterEncoding(encoding); } chain.doFilter(request, response);//到下一個鏈 } public void init(FilterConfig fConfig) throws ServletException { this.config=fConfig; encoding=fConfig.getInitParameter("encoding");//獲得目標編碼格式 } }
3.myfilter.java
package servletbean; import javax.swing.JOptionPane; public class myfilter implements Filter { public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { response.setContentType("text/html"); response.setCharacterEncoding("GB2312"); PrintWriter out=response.getWriter(); String name=""; String age=""; int age1; name=request.getParameter("name"); age=request.getParameter("age"); RequestDispatcher dispatch=request.getRequestDispatcher("erroroutput.jsp"); if(name==null||name==""||name==" "||age==null) { JOptionPane.showMessageDialog(null,"用戶名和年齡輸入錯誤!"); dispatch.forward(request, response); return; } else{ try { age1=Integer.parseInt(age); }catch(Exception e){ //JOptionPane.showMessageDialog(null,"年齡必須為數字!"); dispatch.forward(request,response); return;//如果是錯誤頁面就到erroroutput.jsp中 } } //這裡表示是正確的,也就是說,他回去找下一個鏈,但是它下面已經沒有瞭,所以就會去跳轉頁面瞭,此跳轉的頁面就是action="output.jsp"瞭 chain.doFilter(request, response); } }
Filter中chain.doFilter(req, res)的理解
在寫代碼中,每次看到Filter(過濾器)中 chain.doFilter(req, res);都不懂為什麼要加這一句,他的作用是什麼;
代碼下面也有:
@Override public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { ContentCachingRequestWrapper req=new ContentCachingRequestWrapper((HttpServletRequest) request); ContentCachingResponseWrapper res=new ContentCachingResponseWrapper((HttpServletResponse) response); long startTime = System.currentTimeMillis(); String serverUrl = req.getServletPath(); //不懂這句什麼意思 chain.doFilter(req, res); long endTime = System.currentTimeMillis(); try { int status = res.getStatus(); String charset=res.getCharacterEncoding(); //響應體 String responsePayload = getPayLoad(res.getContentAsByteArray(),res.getCharacterEncoding()); res.copyBodyToResponse(); if(writeLogService==null) { writeLogService = (WriteLogService) ServiceLocator.getInstance().getCtx().getBean("writeLogServiceImpl"); } writeLogService.writeLog(startTime,endTime,serverUrl,postparams,status,responsePayload,charset); } catch (Exception e) { e.printStackTrace(); } }
用法
在doFilter()方法中,在chain.doFilter()之前的代碼,一般是對request執行的過濾操作;
在chain.doFilter()後面的代碼,一般是對response執行的操作;
chain.doFiter()執行下一個過濾器或者業務處理器。
如果在doFilter()方法中,不寫chain.doFilter(),業務無法繼續往下處理;
以上為個人經驗,希望能給大傢一個參考,也希望大傢多多支持WalkonNet。
推薦閱讀:
- Java過濾器doFilter裡chain.doFilter()函數的理解
- springmvc字符編碼過濾器CharacterEncodingFilter的使用
- Java CharacterEncodingFilter案例詳解
- 詳解JavaWeb中的過濾器Filter
- Springboot如何去掉URL後面的jsessionid