JavaWeb 之 Filter过滤器

简介

Filter：过滤器，通过Filter可以拦截访问web资源的请求与响应操作。

Servlet API中提供了一个Filter接口，开发web应用时，如果编写的Java类实现了这个接口，则把这个java类

称之为过滤器。他可以拦截Jsp、Servlet、静态图片文件、静态 html文件等，从而实现一些特殊的功能。

例如：实现URL级别的权限访问控制、过滤敏感词汇、压缩响应信息等一些高级功能。

创建步骤

创建过滤器类并实现Filter接口

在web.xml文件中配置Filter

javax.servlet.Filter接口中的方法介绍：

方法描述

init(FilterConfig fConfig) 初始化方法

doFilter(ServletRequest request, ServletResponse response, FilterChain chain) 过滤方法

destroy() 销毁方法

方法	描述
init(FilterConfig fConfig)	初始化方法
doFilter(ServletRequest request, ServletResponse response, FilterChain chain)	过滤方法
destroy()	销毁方法

1.创建过滤器类并实现Filter接口

public class Filter01 implements Filter {

    public Filter01() {
    }
    
    public void init(FilterConfig fConfig) throws ServletException {
	}

    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        //chain过滤器链
        //注意：如果拦截后不调用doFilter()，请求将无法传到下一个过滤器或服务器里
		//chain.doFilter(request, response);//放行
    }
	public void destroy() {
	}
}

2.在web.xml配置文件中配置过滤器信息

  <filter>
    <filter-name>Filter01</filter-name>
    <filter-class>com.dream.filter.Filter01</filter-class>
  </filter>
  <filter-mapping>
    <filter-name>Filter01</filter-name>
    <url-pattern>/*</url-pattern><!-- 拦截所有请求 -->
  </filter-mapping>

过滤器链

客户端对服务器请求之后，服务器在调用Servlet之前，会执行一组过滤器（多个过滤器），那么这组过滤器就称为一条过滤器链。

生命周期 - 单个过滤器

单个过滤器的生命周期：

项目启动时创建Filter01对象，调用Filter01()、init()

因为此过滤器配置的是所有请求拦截，所以发送请求时，调用doFilter()

项目更新或销毁时，调用destroy()

1.创建过滤器类并实现Filter接口

public class Filter01 implements Filter {
    public Filter01() {
    	System.out.println("Filter01 - Filter01()");
    }
    public void init(FilterConfig fConfig) throws ServletException {
    	System.out.println("Filter01 - init()");
	}
    //doFilter(请求,响应,过滤器链)
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
    	
    	System.out.println("Filter01执行前");
    	chain.doFilter(request, response);//放行
    	System.out.println("Filter01执行后");
	}
	public void destroy() {
		System.out.println("Filter01 - destroy()");
	}
}

2.在web.xml配置文件中配置过滤器信息

  <filter>
    <filter-name>Filter01</filter-name>
    <filter-class>com.dream.filter.Filter01</filter-class>
  </filter>
  <filter-mapping>
    <filter-name>Filter01</filter-name>
    <url-pattern>/*</url-pattern><!-- 拦截所有请求 -->
  </filter-mapping>

生命周期 - 多个过滤器

创建顺序：创建顺序无序

执行顺序：按照web.xml中配置的顺序执行

1.创建过滤器类并实现Filter接口

//----------- Filter01 -----------------------
public class Filter01 implements Filter {
    public Filter01() {
    	System.out.println("Filter01 - Filter01()");
    }
    public void init(FilterConfig fConfig) throws ServletException {
    	System.out.println("Filter01 - init()");
	}
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
    	System.out.println("Filter01执行前");
    	chain.doFilter(request, response);//放行
    	System.out.println("Filter01执行后");
	}
    
	public void destroy() { 
		System.out.println("Filter01 - destroy()");
	}
}
//----------- Filter02 -----------------------
public class Filter02 implements Filter {

	public Filter02() {
		System.out.println("Filter02 - Filter02()");
	}

	public void init(FilterConfig fConfig) throws ServletException {
		System.out.println("Filter02 - init()");
	}
	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
		System.out.println("Filter02执行前");
		chain.doFilter(request, response);//放行
		System.out.println("Filter02执行后");
	}
	public void destroy() { 
		System.out.println("Filter02 - destroy()");
	}
}
//----------- Filter03 -----------------------
public class Filter03 implements Filter {

	public Filter03() {
		System.out.println("Filter03 - Filter03()");
	}

	public void init(FilterConfig fConfig) throws ServletException {
		System.out.println("Filter03 - init()");
	}
	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
		System.out.println("Filter03执行前");
		chain.doFilter(request, response);//放行
		System.out.println("Filter03执行后");
	}
	public void destroy() { 
		System.out.println("Filter03 - destroy()");
	}
}

2.在web.xml配置文件中配置过滤器信息

  <filter>
    <filter-name>Filter01</filter-name>
    <filter-class>com.dream.filter.Filter01</filter-class>
  </filter>
  <filter-mapping>
    <filter-name>Filter01</filter-name>
    <url-pattern>/*</url-pattern><!-- 拦截所有请求 -->
  </filter-mapping>
  
  <filter>
    <filter-name>Filter02</filter-name>
    <filter-class>com.dream.filter.Filter02</filter-class>
  </filter>
  <filter-mapping>
    <filter-name>Filter02</filter-name>
    <url-pattern>/*</url-pattern><!-- 拦截所有请求 -->
  </filter-mapping>
  
  <filter>
    <filter-name>Filter03</filter-name>
    <filter-class>com.dream.filter.Filter03</filter-class>
  </filter>
  <filter-mapping>
    <filter-name>Filter03</filter-name>
    <url-pattern>/*</url-pattern><!-- 拦截所有请求 -->
  </filter-mapping>

案例一：编码过滤器

解决请求和响应乱码问题

public class EncodeFilter implements Filter {
	private String encode;

	public void init(FilterConfig fConfig) throws ServletException {
		//获取web.xml中该过滤器的初始化属性
		encode = fConfig.getInitParameter("encode");
	}

	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {

		HttpServletRequest req = (HttpServletRequest) request;
		HttpServletResponse resp = (HttpServletResponse) response;

		resp.setContentType("text/html;charset="+encode);
		req.setCharacterEncoding(encode);
		
		chain.doFilter(req, resp);
	}
	public void destroy() {
    }
}

  <filter>
    <filter-name>EncodeFilter</filter-name>
    <filter-class>com.dream.filter.EncodeFilter</filter-class>
    <init-param>
    	<param-name>encode</param-name><!-- 初始化参数名 -->
    	<param-value>UTF-8</param-value><!-- 初始化参数值 -->
    </init-param>
  </filter>
  <filter-mapping>
    <filter-name>EncodeFilter</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>

案例二：登录权限过滤器

解决权限的统一控制问题，没有登录，就不能直接跳转到其他详情页面

public class LoginFilter implements Filter {

   public void init(FilterConfig fConfig) throws ServletException {
   }
   public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
   	HttpServletRequest req = (HttpServletRequest) request;
   	HttpServletResponse resp = (HttpServletResponse) response;
   	
   	//获取请求地址
   	String uri = req.getRequestURI();
   	
   	if(uri.contains("welcome.jsp") ||uri.contains("login.jsp") 
   			|| uri.contains("register.jsp") || uri.contains("action=login") 
   			|| uri.contains("action=register")){
   		chain.doFilter(request, response);
   	}else{
   		HttpSession session = req.getSession();
   		String user = (String) session.getAttribute("user");
   		if(user == null){//没登录过
   			resp.sendRedirect("login.jsp");
   		}else{//登录过
   			chain.doFilter(request, response);
   		}
   	}
   }
   public void destroy() {
   }
}

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

案例三：关键字过滤器

解决文档内的一个敏感词汇

public class SensitiveWordsFilter implements Filter {

	public void init(FilterConfig fConfig) throws ServletException {
	}
	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
		
		chain.doFilter(new MyHttpServletRequestWapper((HttpServletRequest) request), response);//放行
	}
	public void destroy() { 
	}

	///请求包装类
	class MyHttpServletRequestWapper extends HttpServletRequestWrapper{
		public MyHttpServletRequestWapper(HttpServletRequest request) {
			super(request);
		}
		@Override
		public String getParameter(String name) {
			
			String value = super.getParameter(name);
			value = value.replaceAll("傻逼", "**");
			//把尖括号替换成字符尖括号，替换后不会认为是html里的尖括号符号
			value = value.replaceAll("<", "&lt;");
			value = value.replaceAll(">", "&gt;");
			
			return value;
		}
	}
}

  <filter>
    <filter-name>SensitiveWordsFilter</filter-name>
    <filter-class>com.dream.filter.SensitiveWordsFilter</filter-class>
  </filter>
  <filter-mapping>
    <filter-name>SensitiveWordsFilter</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>

注解配置过滤器（简化配置）

@WebFilter(

value="/*",

initParams= {@WebInitParam(name = “encode”, value = “UTF-8”),

@WebInitParam(name = “name”, value = “java”)}

)

创建顺序：创建顺序无序

执行顺序：按照类名的顺序执行

@WebFilter(value="/*",initParams={@WebInitParam(name="encode",value="UTF-8")})
public class EncodeFilter implements Filter {
    ...
}

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JavaWeb 之 Filter过滤器

简介

创建步骤

过滤器链

生命周期 - 单个过滤器

生命周期 - 多个过滤器

案例一：编码过滤器

案例二：登录权限过滤器

案例三：关键字过滤器

注解配置过滤器（简化配置）

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