java的Servlet和Filter使用示例

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代码结构如下：

$:~/hotel.com/ROOT #
index.jsp
WEB-INF
	classes
		hello
			HelloFilter.class  HelloServlet.class
	src
		hello
			HelloFilter.java  HelloServlet.java
	web.xml

其中web.xml配置

<?xml version="1.0" encoding="ISO-8859-1"?>
<web-app xmlns="http://java.sun.com/xml/ns/javaee"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
	version="2.5">
	<!--   Please see the "Using Jikes" section of the Jasper-HowTo           -->
	<filter>
		<filter-name>helloFilter</filter-name>
		<filter-class>hello.HelloFilter</filter-class>
	</filter>
	<filter-mapping>
		<filter-name>helloFilter</filter-name>
		<url-pattern>/hello</url-pattern>
	</filter-mapping>

	<servlet>
		<servlet-name>HelloServlet</servlet-name>
		<servlet-class>hello.HelloServlet</servlet-class>
	</servlet>
	<servlet-mapping>
		<servlet-name>HelloServlet</servlet-name>
		<url-pattern>/hello</url-pattern>
	</servlet-mapping>
</web-app>

HelloServlet.java代码如下

package hello;
import java.util.Vector;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.ServletConfig;
import java.io.PrintWriter;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class HelloServlet extends HttpServlet {
	public void init(ServletConfig conf) throws ServletException {
		super.init(conf);
	}
	public void doGet (HttpServletRequest req, HttpServletResponse res)
		throws ServletException, IOException {
		doPost(req, res);
	}
	public void doPost (HttpServletRequest req, HttpServletResponse res)
		throws ServletException, IOException {
		String out = "Hello You";
		PrintWriter writer = res.getWriter();
		writer.write("<html><head></head><body>");
		writer.write(out);
		writer.write("</body></html>");
	} // doPost
}

HelloFilter.java代码如下

package hello;

import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;

public class HelloFilter implements Filter {

	@Override
	public void init(FilterConfig arg0) throws ServletException {
		System.out.println("Filter 初始化");
	}

	@Override
	public void doFilter(ServletRequest req, ServletResponse res,
			FilterChain chain) throws IOException, ServletException {
		HttpServletRequest request = (HttpServletRequest)req;
		System.out.println("拦截 URI="+request.getRequestURI());
		PrintWriter writer = res.getWriter();
		writer.write("<!-- BEGIN -->");
		chain.doFilter(req, res);
		writer.write("<!-- END -->");
	}

	@Override
	public void destroy() {
		System.out.println("Filter 结束");
	}
}

编译运行效果如下

javac -classpath .:/root/apache/apache-tomcat-6.0.37/lib/servlet-api.jar:/usr/share/java/servlet.jar *.java
/usr/share/tomcat6/bin/catalina.sh start

curl 127.0.0.1:8080/hello
<!-- BEGIN --><html><head></head><body>Hello You</body></html><!-- END -->
tail -f /var/log/tomcat6/catalina.out
拦截 URI=/hello

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