实现全局同一编码：Filter

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。

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 = "/*")
public class EncodingFilter implements Filter {

    @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;
        httpServletResponse.setContentType("text/html;charset=UTF-8");
        // 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 {
    }
}

/*
 * 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 {

    private HttpServletRequest request;

    public MyWrapper(HttpServletRequest request) {
        super(request);
        this.request = request;
    }

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

    @Override
    public String getParameter(String name) {
        Map<String, String[]> map = getParameterMap();
        String[] values = map.get(name);
        if (values==null) {
            return null;
        }
        return values[0];
    }

    private boolean flag = true;

    @Override
    public Map<String, String[]> getParameterMap() {
        String method = request.getMethod();
        if ("post".equalsIgnoreCase(method)) {
            try {
                request.setCharacterEncoding("UTF-8");
                return request.getParameterMap();
            } catch (UnsupportedEncodingException e) {
                e.printStackTrace();
            }
        } else if ("Get".equalsIgnoreCase(method)) {

            // get请求
            Map<String, String[]> parameterMap = request.getParameterMap();
            if (!flag) { // 确保get手动编码逻辑只运行一次
                for (String parameterName : parameterMap.keySet()) {
                    String[] values = parameterMap.get(parameterName);
                    if (values != null) {
                        for (int i = 0; i < values.length; i++) {
                            try {
                                // 处理get乱码
                                values[i] = new String(values[i]
                                        .getBytes("ISO-8859-1"), "utf-8");
                            } catch (UnsupportedEncodingException e) {
                                e.printStackTrace();
                            }
                        }
                    }
                }
                flag = true;
            }
            return parameterMap;

        }
        return super.getParameterMap();

    }

}