servlet过滤器简单示例

servlet过滤器的执行顺序

在一个大型项目中往往有多个servlet过滤器，但是这些servlet过滤器的执行顺序是怎样的呢？
请看一下例子：
创建两个简单的servlet文件
package 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;
public class Filter1 implements Filter {
public void destroy() {
}
public void init(FilterConfig config) throws ServletException {
}
public void doFilter(ServletRequest request, ServletResponse response,
  FilterChain chain) throws IOException, ServletException {
 try {
  System.out.println("filter1");
  chain.doFilter(request, response);
  System.out.println("filter1  go back");
 } catch (Exception e) {
  e.printStackTrace();
 }
}
}


package 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;
public class Filter2 implements Filter {
public void destroy() {
}
public void init(FilterConfig config) throws ServletException {
}
public void doFilter(ServletRequest request, ServletResponse response,
  FilterChain chain) throws IOException, ServletException {
 try {
  System.out.println("filter2");
  chain.doFilter(request, response);
  System.out.println("filter2   go back");
 } catch (Exception e) {
  e.printStackTrace();
 }
}
}

在web.xml里面添加映射文件：
<filter>
   <filter-name>filter1</filter-name>
   <filter-class>filter.Filter1</filter-class>
 
 </filter>
 <filter>
   <filter-name>filter2</filter-name>
   <filter-class>filter.Filter2</filter-class>
 </filter>
 <filter>
   <filter-name>filter3</filter-name>
   <filter-class>filter.Filter3</filter-class>
 </filter>
 <filter-mapping>
   <filter-name>filter1</filter-name>
   <url-pattern>/*</url-pattern>
 </filter-mapping>
 <filter-mapping>
   <filter-name>filter2</filter-name>
   <url-pattern>/*</url-pattern>
 </filter-mapping>
对于这个项目的任意一个jsp以及其他请求都要经过这两个servlet过滤器的过滤
因为<url-pattern>/*</url-pattern>
程序执行结果
filter1
filter2
filter2   go back
filter1  go back
如果把web.xml映射文件修改为
</filter>
 <filter>
   <filter-name>filter2</filter-name>
   <filter-class>filter.Filter2</filter-class>
 </filter>
 <filter>
   <filter-name>filter3</filter-name>
   <filter-class>filter.Filter3</filter-class>
 </filter>
<filter-mapping>
   <filter-name>filter2</filter-name>
   <url-pattern>/*</url-pattern>
 </filter-mapping>
 <filter-mapping>
   <filter-name>filter1</filter-name>
   <url-pattern>/*</url-pattern>
 </filter-mapping>
则程序的执行结果为：
filter2
filter1
filter1  go back
filter2   go back

仔细观察这两个映射文件的不同之处我们可以看出
servlet过滤器的执行顺序就是servlet过滤器在web.xml里面映射文件的顺序