一.Filter對亂碼問題的處理

                 web中的配置            

<filter>
  	<filter-name>EncodingFilter</filter-name>
  	<filter-class>com.test.filter.EncodeFilter</filter-class>
  	<init-param>
  		<param-name>Encoding</param-name>
  		<param-value>UTF-8</param-value>
  	</init-param>
  </filter>
  <filter-mapping>
  	<filter-name>EncodingFilter</filter-name>
  	<url-pattern>/*</url-pattern>
  </filter-mapping>
 

package com.test.filter;

import java.io.IOException;
import java.io.UnsupportedEncodingException;

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;


public class EncodeFilter implements Filter{
	
	String encode = null;
	
	public void init(FilterConfig filterConfig) throws ServletException {
		encode = filterConfig.getInitParameter("Encoding");
		System.out.println("Filter init.....");
	}
	
	public void destroy() {
		System.out.println("Filter destroy.....");
	}

	public void doFilter(ServletRequest request, ServletResponse response,
			FilterChain chain) throws IOException, ServletException {
		
		HttpServletRequest req = (HttpServletRequest) request;
		
		if(req.getMethod().equals("GET")) {
			//Get方式處理亂碼
			request = new MyRequest(req);
		} else {
			//post方式處理亂碼
			request.setCharacterEncoding(encode);
		}
		response.setContentType("text/html;charset="+encode);
		//放行
		chain.doFilter(request, response);
		
	}
	
	/**
	 * 內部類裝飾request物件
	 * @author Administrator
	 *
	 */
	class MyRequest extends HttpServletRequestWrapper {
		
		public MyRequest(HttpServletRequest request) {
			super(request);
		}
		
		@Override
		public String getParameter(String name) {
			String value = super.getParameter(name);
			if (value != null) {
				try {
					value = new String(value.getBytes("ISO8859-1"), encode);
				} catch (UnsupportedEncodingException e) {
					e.printStackTrace();
				}
			}
			return value;
		}

		@Override
		public String[] getParameterValues(String name) {
			String[] values = super.getParameterValues(name);
			if (values != null && values.length > 0) {
				for (int i = 0; i < values.length; i++) {
					String value = values[i];
					try {
						values[i] = new String(value.getBytes("ISO8859-1"), encode);
					} catch (UnsupportedEncodingException e) {
						e.printStackTrace();
					}
				}
			}
			return values;
		}
	}

}
 

二.Filter在許可權控制中的應用（登入許可權)

web中filter的註冊

<filter>
  	<filter-name>LoginFilter</filter-name>
  	<filter-class>com.test.filter.LoginFilter</filter-class>
  </filter>
  
  <filter-mapping>
  	<filter-name>LoginFilter</filter-name>
  	<url-pattern>/jsps/*</url-pattern>
  </filter-mapping>
 

package com.test.filter;

import java.io.IOException;

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.HttpServletResponse;
import javax.servlet.http.HttpSession;

import com.test.model.User;

public class LoginFilter implements Filter{

	public void init(FilterConfig arg0) throws ServletException {
		
	}
	public void destroy() {
		
	}

	public void doFilter(ServletRequest request, ServletResponse response,
			FilterChain chain) throws IOException, ServletException {
		
		HttpServletRequest req = (HttpServletRequest) request;
		HttpServletResponse rep = (HttpServletResponse) response;
		HttpSession session = req.getSession();
		//session中取出User物件
		User user = (User) session.getAttribute("user");
		
		if(user != null) {
			//放行
			chain.doFilter(request, response);
		} else {
			//客戶端跳轉
			rep.sendRedirect("/index.jsp");
			//服務端跳轉
			//req.getRequestDispatcher("/index.jsp").forward(request, response);
		}
	}	

}