基础9——过滤器

Posted 2020-10-11 鹏达君

 1.说明：对过滤器的理解我们不要从请求作为起点，而是项目本身的资源作为过滤的起点，然后根据其要过滤的项目资源（url），在根据他的模式，就可以知道它要过滤的是啥资源了，然后看它的方法，就可以知道它过滤是处理些什么逻辑，当然，最后还需要把该请求传下去，如果是后面还有过滤器就继续过滤，如果没有，就到了servlet或者jsp了，而过滤的顺序与其注册的顺序是一致的。

 

2.创建一个过滤器

a.步骤：

1）建一个过滤器，根据需求写好逻辑方法

2）进行注册（xml或者直接注释进行注册）

 

b.代码

package com.guolvqi;

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.annotation.WebFilter;

/**
 * Servlet Filter implementation class fristFilter
 */
//代表过滤映射为/downloadServlet的项目资源
@WebFilter("/downloadServlet")
public class fristFilter implements Filter {

  
	/**
	 * @see Filter#destroy()
	 */
	public void destroy() {
		// TODO Auto-generated method stub
	}

	/**
	 * @see Filter#doFilter(ServletRequest, ServletResponse, FilterChain)
	 */
	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
		System.out.println("过滤器实施了");
		chain.doFilter(request, response);
	}

	/**
	 * @see Filter#init(FilterConfig)
	 */
	public void init(FilterConfig fConfig) throws ServletException {
		// TODO Auto-generated method stub
	}

}

　

3.Filter的生命周期

 

 4.过滤器的api

 

5.过滤器的配置

 

 

5.案例：使用Filter进行字符编码转换

1）servlet

package com.anli;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebFilter;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class TestFilter
 */
@WebServlet("/TestFilter")

public class TestFilter extends HttpServlet {
	private static final long serialVersionUID = 1L;
       
  
	/**
	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		response.getWriter().append("其内容为通过了过滤器设置编码才能正常显示的");
	}

	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		doGet(request, response);
	}

}

　　2）Filter

package com.guolvqi;

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.annotation.WebFilter;
import javax.servlet.annotation.WebInitParam;

/**
 * Servlet Filter implementation class fristFilter
 */
@WebFilter(urlPatterns= {"/*"},
 initParams= {
		 @WebInitParam(name="encoding",value="utf-8"),@WebInitParam(name="encoding1",value="utf-8")})
public class fristFilter implements Filter {
    String enconding;
  
	/**
	 * @see Filter#destroy()
	 */
	public void destroy() {
	enconding=null;
	}

	/**
	 * @see Filter#doFilter(ServletRequest, ServletResponse, FilterChain)
	 */
	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
		if(enconding!=null) {
			//这边的设置既可以是输入的时候输入中文，也可以是输出的时候是中文
			request.setCharacterEncoding(enconding);
			response.setCharacterEncoding(enconding);
		}
		chain.doFilter(request, response);
	}

	/**
	 * @see Filter#init(FilterConfig)
	 */
	public void init(FilterConfig fConfig) throws ServletException {
		enconding=fConfig.getInitParameter("encoding");
	}

}

　　3）测试：