web.xml中filter加载顺序问题

昨天遇到了一个问题，项目中需要用到了urlrewrite，发现地址经过rewrite后，接收到表单post过来的中文数据全是乱码，奇怪了，我的Set Character Encoding这个filter为啥没起作用呢，如下示例，找了半天原因，后来网上找到一篇文章，简单说是filter加载是有顺序的，请看第二个xml，将设置编码方式的filter放到了urlrewrite前面，乱码就不见了，我也不知道具体是为什么，但是通过断点发现这个web.xml中确实是按照你写的先后顺序来执行的，估计是urlrewrite中有转过码，导致filter中再设置编码已经无效。

web.xml示例（接收post中文参数乱码）
<!-- Url Rewrite Filter -->
	<filter>
		<filter-name>UrlRewriteFilter</filter-name>
		<filter-class>org.tuckey.web.filters.urlrewrite.UrlRewriteFilter</filter-class>
        <init-param>
            <param-name>logLevel</param-name>
            <param-value>INFO</param-value>
        </init-param>
	</filter>
	<filter-mapping>
		<filter-name>UrlRewriteFilter</filter-name>
		<url-pattern>/*</url-pattern>
	</filter-mapping>
<!-- Set Character Encoding -->
	<filter>
		<filter-name>Set Character Encoding</filter-name>
		<filter-class>
			org.springframework.web.filter.CharacterEncodingFilter
		</filter-class>
		<init-param>
			<param-name>encoding</param-name>
			<param-value>utf-8</param-value>
		</init-param>
	</filter>
	<filter-mapping>
		<filter-name>Set Character Encoding</filter-name>
		<url-pattern>/*</url-pattern>
	</filter-mapping>

web.xml示例（接收post中文参数没有乱码）
<!-- Set Character Encoding -->
	<filter>
		<filter-name>Set Character Encoding</filter-name>
		<filter-class>
			org.springframework.web.filter.CharacterEncodingFilter
		</filter-class>
		<init-param>
			<param-name>encoding</param-name>
			<param-value>utf-8</param-value>
		</init-param>
	</filter>
	<filter-mapping>
		<filter-name>Set Character Encoding</filter-name>
		<url-pattern>/*</url-pattern>
	</filter-mapping>
<!-- Url Rewrite Filter -->
	<filter>
		<filter-name>UrlRewriteFilter</filter-name>
		<filter-class>org.tuckey.web.filters.urlrewrite.UrlRewriteFilter</filter-class>
        <init-param>
            <param-name>logLevel</param-name>
            <param-value>INFO</param-value>
        </init-param>
	</filter>
	<filter-mapping>
		<filter-name>UrlRewriteFilter</filter-name>
		<url-pattern>/*</url-pattern>
	</filter-mapping>

评论

1 楼 iq527 2010-12-28  

看到这个问题顺便翻了下servlet specification
其中是这样描述的:

    The order the container uses in building the chain of filters to be applied for a 
particular request URI is as follows:
1. First, the <url-pattern> matching filter mappings in the same order that these 
elements appear in the deployment descriptor.
2. Next, the <servlet-name> matching filter mappings in the same order that 
these elements appear in the deployment descriptor.
If a filter mapping contains both <servlet-name> and <url-pattern>, the 
container must expand the filter mapping into multiple filter mappings (one for 
each <servlet-name> and <url-pattern>), preserving the order of the <servlet-
name> and <url-pattern> elements. 

也就是说filter chain
1.首先是根据web.xml中filter的url-pattern的先后顺序来创建
2.然后再按照filter配置中的servlet-name的先后顺序
如果有filter同时配置了url-pattern, servlet-name的话, 则会将该filter mapping拆分成多个filter mapping,同时遵守前面的两条准则