Filter,过滤器
有了 servlet 的经验,学习如何编写和使用 filter 就简单多了。
HelloFilter
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class HelloFilter implements Filter {
@Override
public void init(FilterConfig arg) throws ServletException {
System.out.println("HelloFilter initialized");
}
@Override
public void doFilter(ServletRequest req, ServletResponse res,
FilterChain chain) throws IOException, ServletException {
HttpServletRequest request = (HttpServletRequest)req;
System.out.println("HelloFilter touched by " + request.getRequestURI());
chain.doFilter(req, res);
}
@Override
public void destroy() {
System.out.println("HelloFilter destroyed");
}
}
编译
Filter 的编译同样依赖 servlet-api:
javac -cp ${CATALINA_BASE}/lib/servlet-api.jar HelloFilter.java
在 Tomcat 中使用 Filter
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
version="4.0"
metadata-complete="true">
<filter>
<filter-name>hello</filter-name>
<filter-class>HelloFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>hello</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
<servlet>
<servlet-name>hello</servlet-name>
<servlet-class>HelloWorld</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>hello</servlet-name>
<url-pattern>/hello</url-pattern>
</servlet-mapping>
</web-app>