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Servlet生命周期
ServletConfig和ServletContext
演示Servlet的生命周期:
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" version="2.5">
<display-name>Servlet04</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>
<servlet-name>demo</servlet-name>
<servlet-class>web.DemoServlet</servlet-class>
<!-- 服务器启动时第1个加载此Servlet -->
<load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>demo</servlet-name>
<url-pattern>/demo</url-pattern>
</servlet-mapping>
</web-app>
DemoServlet.java
package web;
import java.io.IOException;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class DemoServlet extends HttpServlet{
public DemoServlet() {
System.out.println("创建DemoServlet");
}
@Override
protected void service(HttpServletRequest req,
HttpServletResponse res) throws ServletException, IOException {
System.out.println("调用DemoServlet");
}
@Override
public void destroy() {
super.destroy();
System.out.println("销毁DemoServlet");
}
@Override
public void init() throws ServletException {
super.init();
System.out.println("初始化DemoServlet");
}
@Override
public void init(ServletConfig arg0) throws ServletException {
super.init(arg0);
System.out.println("初始化DemoServlet---ServletConfig");
}
}
将Servlet04工程部署到Tomcat上,运行Tomcat启动案例工程,
浏览器录入http://localhost:8080/Servlet04//demo 即可:如果没有错误,最终后台输出效果应如下图:
可见在启动服务器时自动创建初始化对象DemoServlet对象
当我们不停调用DemoServlet对象时不会再次创建和初始化对象
ServletConfig和ServletContext演示
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" version="2.5">
<display-name>Servlet04</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>
<servlet-name>demo</servlet-name>
<servlet-class>web.DemoServlet</servlet-class>
<!-- 服务器启动时第1个加载此Servlet -->
<load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>demo</servlet-name>
<url-pattern>/demo</url-pattern>
</servlet-mapping>
<servlet>
<servlet-name>login</servlet-name>
<servlet-class>web.LoginServlet</servlet-class>
<!-- 预置一个数据 -->
<init-param>
<param-name>maxOnline</param-name>
<param-value>2000</param-value>
</init-param>
</servlet>
<servlet-mapping>
<servlet-name>login</servlet-name>
<url-pattern>/login</url-pattern>
</servlet-mapping>
<!-- 预置一份共用的数据 -->
<context-param>
<param-name>size</param-name>
<param-value>10</param-value>
</context-param>
<servlet>
<servlet-name>findEmp</servlet-name>
<servlet-class>web.FindEmpServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>findEmp</servlet-name>
<url-pattern>/findEmp</url-pattern>
</servlet-mapping>
<servlet>
<servlet-name>findDept</servlet-name>
<servlet-class>web.FindDeptServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>findDept</servlet-name>
<url-pattern>/findDept</url-pattern>
</servlet-mapping>
<servlet>
<servlet-name>init</servlet-name>
<servlet-class>web.InitServlet</servlet-class>
<load-on-startup>2</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>init</servlet-name>
<url-pattern>/init</url-pattern>
</servlet-mapping>
</web-app>
LoginServlet:
package web;
import java.io.IOException;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class LoginServlet extends HttpServlet{
@Override
protected void service(HttpServletRequest req,
HttpServletResponse res) throws ServletException, IOException {
//读取预置的私有的数据
ServletConfig cfg = this.getServletConfig();
System.out.println(cfg.getInitParameter("maxOnline"));
}
}
InitServlet
package web;
import javax.servlet.ServletConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
public class InitServlet extends HttpServlet{
@Override
public void init(ServletConfig arg0) throws ServletException {
super.init(arg0);
//Tomcat启动时调用此方法,
//将流量count初始化为0,
//并写入ServletContext,
//便于访问其他Servlet时统计流量。
ServletContext ctx = getServletContext();
ctx.setAttribute("count", 0);
}
}
FindEmpServlet
package web;
import java.io.IOException;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class FindEmpServlet extends HttpServlet{
@Override
protected void service(HttpServletRequest arg0,
HttpServletResponse arg1) throws ServletException, IOException {
System.out.println("FindEmpServlet");
//获取预置的共用的数据
ServletContext ctx = this.getServletContext();
System.out.println(ctx.getInitParameter("size"));
//流量累加
Object count = ctx.getAttribute("count");
int c = Integer.parseInt(count.toString())+1;
ctx.setAttribute("count", c);
System.out.println(ctx.getAttribute("count"));
}
}
FindDeptServlet
package web;
import java.io.IOException;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class FindDeptServlet extends HttpServlet{
@Override
protected void service(HttpServletRequest req,
HttpServletResponse res) throws ServletException, IOException {
System.out.println("FindDeptServlet");
//获取预置的共用的数据
ServletContext ctx = this.getServletContext();
System.out.println(ctx.getInitParameter("size"));
//流量累加
Object count = ctx.getAttribute("count");
int c = Integer.parseInt(count.toString())+1;
ctx.setAttribute("count", c);
System.out.println(ctx.getAttribute("count"));
}
}
将Servlet04工程部署到Tomcat上,运行Tomcat启动案例工程,
浏览器录入http://localhost:8080/Servlet04//login即可:如果没有错误,最终控制台输出效果应如下图:
输出即为配置的参数2000
将Servlet04工程部署到Tomcat上,运行Tomcat启动案例工程,
浏览器录入http://localhost:8080/Servlet04//findEmp
http://localhost:8080/Servlet04//findDept
输出即为配置的参数10,并且设置的动态参数count累加成功
如果没有错误,最终控制台输出效果应如下图: