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;
    }
}