实现全局同一编码：Filter

Posted 2020-09-07 第九种格调的人生

1. request.setCharacterEncoding("UTF-8");只对POST方式提交有用
2. 对于GET方式 ，可以有装饰模式和适配器模式，对获取参数的函数进行重写。
3. 对所有的页面进行过滤，设置编码。

4. package com.learning.filter;
   
   import java.io.IOException;
   import java.io.UnsupportedEncodingException;
   import java.util.Enumeration;
   import java.util.Map;
   
   import javax.security.auth.message.callback.PrivateKeyCallback.Request;
   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.annotation.WebInitParam;
   import javax.servlet.http.HttpServletRequest;
   import javax.servlet.http.HttpServletRequestWrapper;
   import javax.servlet.http.HttpServletResponse;
   
   @WebFilter(urlPatterns = "/*", initParams = { @WebInitParam(name = "encoding", value = "UTF-8") })
   public class EncodingFilter implements Filter {
   
       private FilterConfig filterConfig;
   
       @Override
       public void destroy() {
   
       }
   
       @Override
       public void doFilter(ServletRequest arg0, ServletResponse arg1, FilterChain arg2)
               throws IOException, ServletException {
           // 转换对象
           HttpServletRequest httpServletRequest = (HttpServletRequest) arg0;
           HttpServletResponse httpServletResponse = (HttpServletResponse) arg1;
           // 得到初始化参数
           String encoding = filterConfig.getInitParameter("encoding");
           // 当前不是UTF-8编码 就设置为UTF-8 但此方式之适合POST方式提交
           httpServletRequest.setCharacterEncoding(encoding);
   
           // 对GET方式支持中文提交，可以应用装饰模式或适配器模式 （ 便于观看代码 此类写在本类之下 ）
           httpServletRequest = new MyWrapper(httpServletRequest);
           arg2.doFilter(httpServletRequest, httpServletResponse);
       }
   
       @Override
       public void init(FilterConfig filterConfig) throws ServletException {
           this.filterConfig = filterConfig;
       }
   }
   
   /*
    装饰模式实现：
    1.实现被包装对象的接口 或者 继承被包装对象的自带装饰类 
    2.声明一个和被包装对象相同的对象 用于传参 
    3.运用构造函数 
    4.对需要重写的方法进行重写
    */
   class MyWrapper extends HttpServletRequestWrapper {
   
       HttpServletRequest request;
   
       public MyWrapper(HttpServletRequest request) {
           super(request);
           this.request = request;
       }
   
       @Override
       public String[] getParameterValues(String name) {
           Map<String, String[]> map = request.getParameterMap();
           String[] values = map.get(name);
           return values;
       }
   
       @Override
       public String getParameter(String name) {
           Map<String, String[]> map = request.getParameterMap();
           String[] values = map.get(name);
           return values[0];
       }
   
       private boolean flag = true;
   
       @Override
       public Map<String, String[]> getParameterMap() {
           Map<String, String[]> map = request.getParameterMap();
           // 只对第一次访问编码，
           if (flag) {
               for (Map.Entry<String, String[]> m : map.entrySet()) {
                   String[] values = m.getValue();
                   for (int i = 0; i < values.length; i++) {
                       try {
                           values[i] = new String(values[i].getBytes("iso-8859-1"), "utf-8");
                       } catch (UnsupportedEncodingException e) {
                           e.printStackTrace();
                       }
                   }
               }
               flag = false;
           }
           return map;
       }
   
   }