Filter （一）

来源：互联网发布：伍迪艾伦知乎编辑：程序博客网时间：2024/06/05 11:58

理解Filter的执行顺序。

我们可以在web.xml中定义多个Filter，顺序很重要，从上往下的顺序。doFilter方法中的chain.doFilter(request, response)这一句，就是处理完当前这一句代码之前的代码后，接着处理下一个Filter。

执行顺序如下，假设有N个Filter，这里是三个。

web.xml :

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5">
<display-name>TestFilter</display-name>
<welcome-file-list>
<welcome-file>index.html</welcome-file>
<welcome-file>index.htm</welcome-file>
<welcome-file>index.jsp</welcome-file>
<welcome-file>default.html</welcome-file>
<welcome-file>default.htm</welcome-file>
<welcome-file>default.jsp</welcome-file>
</welcome-file-list>
<servlet>
<description></description>
<display-name>MyServlet</display-name>
<servlet-name>MyServlet</servlet-name>
<servlet-class>com.test.MyServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>MyServlet</servlet-name>
<url-pattern>/MyServlet</url-pattern>
</servlet-mapping>
<filter>
<display-name>Filter1</display-name>
<filter-name>Filter1</filter-name>
<filter-class>com.test.Filter1</filter-class>
</filter>
<filter-mapping>
<filter-name>Filter1</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
<filter>
<display-name>Filter2</display-name>
<filter-name>Filter2</filter-name>
<filter-class>com.test.Filter2</filter-class>
</filter>
<filter-mapping>
<filter-name>Filter2</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
<filter>
<display-name>Filter3</display-name>
<filter-name>Filter3</filter-name>
<filter-class>com.test.Filter3</filter-class>
</filter>
<filter-mapping>
<filter-name>Filter3</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
</web-app>

servlet如下：

public class MyServlet extends HttpServlet {
private static final long serialVersionUID = 1L;

/**
* @see HttpServlet#HttpServlet()
*/
public MyServlet() {
super();
// TODO Auto-generated constructor stub
}

/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
System.out.println("这里是处理servlet的代码。");
}

/**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
*/
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
}

}

下面是三个Filter：

public class Filter1 implements Filter {

/**
* Default constructor.
*/
public Filter1() {
// TODO Auto-generated constructor stub
}

/**
* @see Filter#destroy()
*/
public void destroy() {
// TODO Auto-generated method stub
}

/**
* @see Filter#doFilter(ServletRequest, ServletResponse, FilterChain)
*/
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
System.out.println("------> Filter 1 中 chain.doFilter(request, response) 之前的代码");
chain.doFilter(request, response);
System.out.println("------> Filter 1 中 chain.doFilter(request, response) 之后的代码");
}

/**
* @see Filter#init(FilterConfig)
*/
public void init(FilterConfig fConfig) throws ServletException {
// TODO Auto-generated method stub
}

}

-------------------------------------

public class Filter2 implements Filter {

/**
* Default constructor.
*/
public Filter2() {
// TODO Auto-generated constructor stub
}

/**
* @see Filter#destroy()
*/
public void destroy() {
// TODO Auto-generated method stub
}

/**
* @see Filter#doFilter(ServletRequest, ServletResponse, FilterChain)
*/
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
System.out.println("------> Filter 2 中 chain.doFilter(request, response) 之前的代码");
chain.doFilter(request, response);
System.out.println("------> Filter 2 中 chain.doFilter(request, response) 之后的代码");
}

/**
* @see Filter#init(FilterConfig)
*/
public void init(FilterConfig fConfig) throws ServletException {
// TODO Auto-generated method stub
}

}

------------------------------------

public class Filter3 implements Filter {

/**
* Default constructor.
*/
public Filter3() {
// TODO Auto-generated constructor stub
}

/**
* @see Filter#destroy()
*/
public void destroy() {
// TODO Auto-generated method stub
}

/**
* @see Filter#doFilter(ServletRequest, ServletResponse, FilterChain)
*/
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
System.out.println("------> Filter 3 中 chain.doFilter(request, response) 之前的代码");
chain.doFilter(request, response);
System.out.println("------> Filter 3 中 chain.doFilter(request, response) 之后的代码");
}

/**
* @see Filter#init(FilterConfig)
*/
public void init(FilterConfig fConfig) throws ServletException {
// TODO Auto-generated method stub
}

}

执行结果如下：

在浏览器中输入http://localhost:8080/TestFilter/MyServlet执行，控制台打印如下：

------> Filter 1 中 chain.doFilter(request, response) 之前的代码
------> Filter 2 中 chain.doFilter(request, response) 之前的代码
------> Filter 3 中 chain.doFilter(request, response) 之前的代码
这里是处理servlet的代码。
------> Filter 3 中 chain.doFilter(request, response) 之后的代码
------> Filter 2 中 chain.doFilter(request, response) 之后的代码
------> Filter 1 中 chain.doFilter(request, response) 之后的代码

0 0