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.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;
import javax.servlet.http.HttpServletResponse;

//全局编码过滤
public class EncodingFilter implements Filter {
	public void destroy() {

	}

	public void doFilter(ServletRequest req, ServletResponse resp,
			FilterChain chain) throws IOException, ServletException {

		// 1.将请求与响应对象强制转换成http协议下的
		HttpServletRequest request = (HttpServletRequest) req;
		HttpServletResponse response = (HttpServletResponse) resp;

		// 2.完成操作--处理编码

		// 将request对象进行增强，增强后的request对象可以解决编码问题----使用装饰来增强.

		// 3.放行
		chain.doFilter(new MyRequest(request), response);
	}

	public void init(FilterConfig arg0) throws ServletException {

	}
}

// 自定义的的增强类
class MyRequest extends HttpServletRequestWrapper {

	private HttpServletRequest request;

	private boolean flag = true;// 开关

	public MyRequest(HttpServletRequest request) {
		super(request);
		this.request = request;

	}

	// 得写方法，来解决编码问题
	@Override
	public String getParameter(String name) {
		if (name == null) {
			return null;
		}
		String[] st = getParameterMap().get(name);
		if (st == null || st.length == 0) {
			return null;
		}

		return st[0];
	}

	@Override
	public String[] getParameterValues(String name) {
		if (name == null) {
			return null;
		}
		String[] st = getParameterMap().get(name);

		return st;
	}

	@Override
	public Map<String, String[]> getParameterMap() {

		// 1.得到请求方式
		String method = request.getMethod();

		if ("post".equalsIgnoreCase(method)) {
			// 解决post编码
			try {
				request.setCharacterEncoding("utf-8");
			} catch (UnsupportedEncodingException e) {
				e.printStackTrace();
			}
			return request.getParameterMap();
		} else {
			// get请求
			// 2.得到所有请求参数
			Map<String, String[]> map = request.getParameterMap();

			if (flag) { // 对map集合中的信息只进行一次转码

				// 3.对Map集合中的value的每一个元素进行转码操作

				for (String key : map.keySet()) { // 得到map的所有的key

					String[] value = map.get(key); // 根据key获取value

					// 4.对value中所有元素进行编码处理
					for (int i = 0; i < value.length; i++) {

						try {
							value[i] = new String(
									value[i].getBytes("iso8859-1"), "utf-8");
						} catch (UnsupportedEncodingException e) {
							e.printStackTrace();
						}

					}

				}
				flag = false;
			}

			return map;

		}

	}

}

web.xml配置

<!-- 全局编码过滤器 -->
	<filter>
		<filter-name>encoding</filter-name>
		<filter-class>cn.itcast.web.filter.EncodingFilter</filter-class>
	</filter>

	<filter-mapping>
		<filter-name>encoding</filter-name>
		<url-pattern>/*</url-pattern>
	</filter-mapping>