Filter过滤器的应用--处理字符编码

骑猪看日落 2022-06-09 09:26 214阅读 0赞

Filter是servlet里的过滤器，如果你想过滤某个servlet，你就可以使用filter，然后再类体中通过chain语句来选择是否放行，如果放行，servlet会得到执行，如果不放行，filter就像一堵墙，servlet返回给浏览器将得不到执行

以下通过代码来实现将经过过滤器的代码进行字符编码设置。

package com.zhang;  
  
  
import java.io.IOException;  
import java.io.UnsupportedEncodingException;  
import java.util.Map;  
  
  
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.HttpServletRequestWrapper;  
  
  
public class EncodingFilter implements Filter\{  
//一次性处理字符编码问题  
  
  
//执行是否放行的方法  
@Override  
public void doFilter(ServletRequest request, ServletResponse response,  
FilterChain chain) throws IOException, ServletException \{  
// TODO Auto-generated method stub  
  
//获取请求,装饰者模式  
HttpServletRequest httpServletRequest = (HttpServletRequest)request;  
HttpServletRequest myRequest = new MyRequest(httpServletRequest);  
//处理相应的乱码  
response.setContentType("text/html;charset=utf-8");  
//放行  
chain.doFilter(myRequest, response);  
\}  
  
//自定义的request对象  
// 自己用自己定义的request处理字符编码问题  
class MyRequest extends HttpServletRequestWrapper\{  
  
  
private HttpServletRequest request;  
private boolean hasEncode = false;  
  
public MyRequest(HttpServletRequest request) \{  
super(request);  
this.request = request;  
\}  
//重写这个方法，在内部吧map里的中文乱码处理掉  
@Override  
public Map<String, String\[\]> getParameterMap() \{  
// TODO Auto-generated method stub  
String method = request.getMethod();  
if("post".equalsIgnoreCase(method))\{  
try \{  
request.setCharacterEncoding("utf-8");  
return request.getParameterMap();  
\} catch (UnsupportedEncodingException e) \{  
// TODO Auto-generated catch block  
e.printStackTrace();  
\}  
\}else if("get".equalsIgnoreCase(method))\{  
//处理get的乱码  
Map<String, String\[\]> parameterMap = request.getParameterMap();  
//对于每一个内容都要重新编码  
if(! hasEncode)\{  
for(String parameterName:parameterMap.keySet())\{  
//拿到键值，单不确定几个值  
String \[\] value = parameterMap.get(parameterName);  
if(value!=null)\{  
for(int i=0; i < value.length; i++)\{  
try \{  
value\[i\] = new String(  
value\[i\].getBytes("ISO-8859-1"),"UTF-8");  
\} catch (UnsupportedEncodingException e) \{  
// TODO Auto-generated catch block  
e.printStackTrace();  
\}  
\}  
\}  
  
\}  
hasEncode=true;  
\}  
return parameterMap;  
\}  
  
return super.getParameterMap();  
\}  
@Override  
public String getParameter(String name) \{  
// TODO Auto-generated method stub  
//通过自己定义的已经处理过字符编码问题方法获取map  
Map<String, String\[\]> parameterMap=getParameterMap();  
//根据map获取值，值是数组  
String \[\] value=parameterMap.get(name);  
if(value==null)\{  
return null;  
\}  
//取一个值就是数组第0个元素  
return value\[0\];  
  
  
\}  
  
@Override  
public String\[\] getParameterValues(String name) \{  
// TODO Auto-generated method stub  
Map<String, String\[\]> parameterMap = getParameterMap();  
String\[\] value = parameterMap.get(name);  
return value;  
\}  
  
  
\}  
  
  
@Override  
public void init(FilterConfig arg0) throws ServletException \{  
// TODO Auto-generated method stub  
  
\}  
@Override  
public void destroy() \{  
// TODO Auto-generated method stub  
  
\}  
\}

主要是重写getParameterMap()方法，让取得的数据在方法里面直接转码，分为post和get请求，分几种不同的情况讨论，如上代码