Filter - 全局编码 (装饰者模式)

Tomcat7以前需要处理get乱码，tomcat8以后不需要处理get乱码，因为tomcat内部会处理。

乱码原因：

 package cn.itcast.web.filter;

 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.annotation.WebFilter;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletRequestWrapper;

 /**
  * 编码过滤器（用于统一项目编码，防止出现乱码）
  */
 @WebFilter("/*")
 public class EncodingFilter2 implements Filter {
     public void init(FilterConfig filterConfig) throws ServletException {

     }

     public void doFilter(ServletRequest request, ServletResponse response,
                          FilterChain chain) throws IOException, ServletException {
         // 处理请求乱码
         HttpServletRequest httpServletRequest = (HttpServletRequest) request;
         HttpServletRequest myRequest = new MyRequest(httpServletRequest);
         // 处理响应乱码
         response.setContentType("text/html;charset=utf-8");
         chain.doFilter(myRequest, response);
     }

     public void destroy() {

     }
 }

 // 自定义request对象
 class MyRequest extends HttpServletRequestWrapper {
     private HttpServletRequest request;

     public MyRequest(HttpServletRequest request) {
         super(request);// super必须写
         this.request = request;
     }

     // 对需要增强方法 进行覆盖
     @SuppressWarnings({"unchecked", "rawtypes"})
     @Override
     public Map getParameterMap() {
         // 先获得请求方式
         String method = request.getMethod();
         if (method.equalsIgnoreCase("post")) {
             // post请求
             try {
                 // 处理post乱码
                 request.setCharacterEncoding("utf-8");
                 return request.getParameterMap();
             } catch (UnsupportedEncodingException e) {
                 e.printStackTrace();
             }
         } else if (method.equalsIgnoreCase("get")) {
             // get请求
             Map<String, String[]> parameterMap = request.getParameterMap();
             for (String parameterName : parameterMap.keySet()) {
                 String[] values = parameterMap.get(parameterName);
                 if (values != null) {
                     for (int i = 0; i < values.length; i++) {
                         try {
                             values[i] = new String(values[i].getBytes("iso8859-1"), "utf-8");
                         } catch (UnsupportedEncodingException e) {
                             e.printStackTrace();
                         }
                     }
                 }
             }
             return parameterMap;
         }
         return super.getParameterMap();
     }

     @Override
     public String getParameter(String name) {
         @SuppressWarnings("unchecked")
         Map<String, String[]> parameterMap = getParameterMap();
         String[] values = parameterMap.get(name);
         if (values == null) {
             return null;
         }
         return values[0]; // 取回参数的第一个值
     }

     @Override
     public String[] getParameterValues(String name) {
         @SuppressWarnings("unchecked")
         Map<String, String[]> parameterMap = getParameterMap();
         String[] values = parameterMap.get(name);
         return values;
     }
 }