javax.servlet.*,javax.servlet.http.*包应用-Filter-优快云博客

本文详细介绍了Servlet过滤器的配置及工作原理，展示了如何通过web.xml文件定义过滤器，并提供了具体的Java代码实现。过滤器可以对客户端请求进行过滤和校验，确保请求的有效性。

A filter is an object that performs filtering tasks on either the request to a resource (a servlet or static content), or on the response from a resource, or both.

Filter是针对客户端向服务器请求资源的时候,过滤和校验该请求是否有效的一种方式,其具体的实现方式是.在web.xml中定义
<filter></filter>

xml 代码

<filter>
<filter-name>myFilter</filter-name>
<filter-class>com.test.MyFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>myFilter</filter-name>
<servlet-name>myServlet</servlet-name>
</filter-mapping>
<servlet>
<servlet-name>myServlet</servlet-name>
<servlet-class>com.test.MyServlet</servlet-class>
<load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>myServlet</servlet-name>
<url-pattern>/myServlet</url-pattern>
</servlet-mapping>

上面是请求一个myServlet时候,myFilter对其该请求过滤.代码如下:

java 代码

package com.test;
import javax.servlet.Filter;
import javax.servlet.FilterConfig;
import javax.servlet.FilterChain;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletResponse;
public class MyFilter implements Filter {
public void init(FilterConfig filterConfig) {
}
public void destroy() {
}
public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain) {
String testValue = request.getParameter("TestValue");
System.out.println("TestValue="+testValue);
try {
if (testValue.equals("1"))
chain.doFilter(request, response);
else{
((HttpServletResponse)response).sendRedirect("index.jsp");
}
} catch (Exception e) {
e.printStackTrace();
}
}
}