web.xml中的filter配置+spring filter配置中targetFilterLifecycle属性作用

缺乏、安全感 2021-06-22 15:36 424阅读 0赞

我们平时写过滤器一般有一下两种，以日志过滤器为例：

<filter>
            <filter-name>logFilter</filter-name>
            <filter-class>cn.com.common.filter.LogFilter</filter-class>
        </filter>
        <filter-mapping>
            <filter-name>logFilter</filter-name>
            <url-pattern>/web/*</url-pattern>
        </filter-mapping>    
        
        <filter>
            <filter-name>logFilter2</filter-name>
            <filter-class>org.springframework.web.filter.DelegatingFilterProxy</filter-class>
            <init-param>
                <param-name>targetFilterLifecycle</param-name>
                <param-value>true</param-value>
            </init-param>
        </filter>
        <filter-mapping>
            <filter-name>logFilter2</filter-name>
            <url-pattern>/web/*</url-pattern>
        </filter-mapping>
        
        <bean class="cn.com.common.filter.LogFilter2" id="logFilter2"></bean>

第一种是我们最常见的filter，指定filter-name，filter-class，和filter映射关系。这种写法与spring无关，就像是一个servlet，唯一的区别在于servlet只处理一段业务并返回，而filter过滤后还可以传递给下一个filter。

第二种是与spring集成的写法，filter-class是spring的一个代理，这个代理也是一个filter。

这是DelegatingFilterProxy的doFilter方法：

@Override
    	public void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain)
    			throws ServletException, IOException {
    
    		// Lazily initialize the delegate if necessary.
    		Filter delegateToUse = this.delegate;
    		if (delegateToUse == null) {
    			synchronized (this.delegateMonitor) {
    				if (this.delegate == null) {
    					WebApplicationContext wac = findWebApplicationContext();
    					if (wac == null) {
    						throw new IllegalStateException("No WebApplicationContext found: no ContextLoaderListener registered?");
    					}
    					this.delegate = initDelegate(wac);
    				}
    				delegateToUse = this.delegate;
    			}
    		}
    
    		// Let the delegate perform the actual doFilter operation.
    		invokeDelegate(delegateToUse, request, response, filterChain);
    	}

可见，当没有委托filter时，它会从spring上下文中寻找这个filter。而且是根据beanName查找。

protected Filter initDelegate(WebApplicationContext wac) throws ServletException {
    		Filter delegate = wac.getBean(getTargetBeanName(), Filter.class);
    		if (isTargetFilterLifecycle()) {
    			delegate.init(getFilterConfig());
    		}
    		return delegate;
    	}

找到这个filter bean之后，执行invokeDelegate，

/**
    	 * Actually invoke the delegate Filter with the given request and response.
    	 * @param delegate the delegate Filter
    	 * @param request the current HTTP request
    	 * @param response the current HTTP response
    	 * @param filterChain the current FilterChain
    	 * @throws ServletException if thrown by the Filter
    	 * @throws IOException if thrown by the Filter
    	 */
    	protected void invokeDelegate(
    			Filter delegate, ServletRequest request, ServletResponse response, FilterChain filterChain)
    			throws ServletException, IOException {
    
    		delegate.doFilter(request, response, filterChain);
    	}

可见是直接调filter bean的doFilter方法，与第一种就一样了。

下面说一下targetFilterLifecycle参数的作用：

字面义是目标过滤器的全生命周期，如果为true，就对filter的全生命周期（init，dofilter，destroy）进行代理，为false则只对dofilter方法进行代理。默认为false，不会执行filter bean里面init和destroy方法。

使用的时候按照是否需要重写init，destroy方法来确认配成true还是false。

### 贴下测试代码： ###

public class LogFilter implements Filter {
    	@Override
    	public void init(FilterConfig filterConfig) throws ServletException {
    		System.out.println("LogFilter1init");
    	}
    	@Override
    	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
    		System.out.println("LogFilter1doFilter");
    		chain.doFilter(request, response);
    	}
    	@Override
    	public void destroy() {
    		System.out.println("LogFilter1destroy");
    	}
    }

public class LogFilter2 implements Filter {
    	@Override
    	public void init(FilterConfig filterConfig) throws ServletException {
    		System.out.println("LogFilter2init");
    	}
    	@Override
    	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
    		System.out.println("LogFilter2doFilter");
    		chain.doFilter(request,response);
    	}
    	@Override
    	public void destroy() {
    		System.out.println("LogFilter2destroy");
    	}
    }

web.xml

<?xml version="1.0" encoding="UTF-8"?>
    <web-app version="2.4"
             xmlns="http://java.sun.com/xml/ns/j2ee"
             xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
             xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
      
        <context-param>
            <param-name>spring.profiles.default</param-name>
            <param-value>dev</param-value>
        </context-param>
        
        <context-param>
            <param-name>contextConfigLocation</param-name>
            <param-value>
                classpath*:/spring/applicationContext.xml
            </param-value>
        </context-param>
        
        <listener>
            <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
        </listener>
    
        
        
        <filter>
            <filter-name>logFilter2</filter-name>
            <filter-class>org.springframework.web.filter.DelegatingFilterProxy</filter-class>
            <init-param>
                <param-name>targetFilterLifecycle</param-name>
                <param-value>true</param-value>
            </init-param>
        </filter>
        <filter-mapping>
            <filter-name>logFilter2</filter-name>
            <url-pattern>/web/*</url-pattern>
        </filter-mapping>
        
        <filter>
            <filter-name>logFilter</filter-name>
            <filter-class>cn.com.common.filter.LogFilter</filter-class>
        </filter>
        <filter-mapping>
            <filter-name>logFilter</filter-name>
            <url-pattern>/web/*</url-pattern>
        </filter-mapping>
    </web-app>

applicationContext.xml

<?xml version="1.0" encoding="UTF-8"?>
    
    <beans xmlns="http://www.springframework.org/schema/beans"
    	   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    	   xmlns:util="http://www.springframework.org/schema/util"
    	   xmlns:context="http://www.springframework.org/schema/context"
    	   xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.0.xsd
                               http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-2.0.xsd
                               http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd">
    
    <bean class="cn.com.common.filter.LogFilter2" id="logFilter2"></bean>
    </beans>

初始化和过滤结果：

LogFilter2init
    LogFilter1init
    
    LogFilter2doFilter
    LogFilter1doFilter