Servlet相关
目录
5、ServletConfig读取servlet配置中的信息
简介
Servlet（Server Applet）是Java Servlet的简称，称为小服务程序或服务连接器，用Java编写的服务器端程序，主要功能在于交互式地浏览和修改数据，生成动态Web内容。
接收客户端请求及响应客户端。
1、最简单的servlet
在src下面写一个Servlet类实现Servlet接口
package com.zhujunwei.servlet;
import java.io.IOException;
import javax.servlet.Servlet;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
/**
*
* @author Administrator
* 创建一个Servlet，使该Servlet实现Servlet接口：实现5个抽象方法
*
*/
public class HelloServlet implements Servlet
{
@Override
public void service(ServletRequest arg0, ServletResponse arg1) throws ServletException, IOException
{
System.out.println("Hello Servlet...");
}
@Override
public void destroy()
{
}
@Override
public ServletConfig getServletConfig()
{
return null;
}
@Override
public String getServletInfo()
{
return null;
}
@Override
public void init(ServletConfig arg0) throws ServletException
{
}
}
写完java文件后需要在WebContent/WEB-INF/web.xml配置servlet
...
<welcome-file>default.jsp</welcome-file>
</welcome-file-list>
<servlet>
<servlet-name>HelloServlet</servlet-name>
<servlet-class>com.zhujunwei.servlet.HelloServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>HelloServlet</servlet-name>
<url-pattern>/HelloServlet</url-pattern>
</servlet-mapping>
</web-app>打开服务器，将项目部署到服务器上，在浏览中输入
http://localhost:8080/Hello/HelloServlet可以在控制台看到
Hello Servlet...2、继承HttpServlet
继续在src下面创建新的类，这次不是实现Servlet接口，而是继承HttpServlet类（Servlet的子类）
package com.zhujunwei.servlet;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
*
* @author Administrator
* 创建一个Servlet，使该Servlet继承HttpServlet(Servlet接口的子类)
*
* HttpServlet类实现了Servlet的方法
*
*/
public class HelloServlet02 extends HttpServlet
{
/*@Override
protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException
{
System.out.println("HelloServlet02----");
}*/
private static final long serialVersionUID = 1L;
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException
{
System.out.println("doGet...");
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException
{
System.out.println("doPost...");
}
}
接着配置web.xml
...
<servlet>
<servlet-name>HelloServlet02</servlet-name>
<servlet-class>com.zhujunwei.servlet.HelloServlet02</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>HelloServlet02</servlet-name>
<url-pattern>/HelloServlet02</url-pattern>
</servlet-mapping>
</web-app>重启服务器，在地址栏输入
http://localhost:8080/Hello/HelloServlet02可以在控制台看到
doGet...3、Servlet的生命周期
Servlet只会在第一次调用时创建，调用init()方法（就像类的构造器一样），而在以后的调用中只会调用service方法。
destroy()方法只会在服务器关闭或者项目从服务器中移除的时候调用。
实例演示：
创建Servlet类
package com.zhujunwei.servlet;
import java.io.IOException;
import javax.servlet.Servlet;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
/**
*
* @author Administrator
* 演示生命活动的生命周期
*
*/
public class HelloServlet03 implements Servlet
{
@Override
public void destroy()
{
System.out.println("Servlet destroy()....");
}
@Override
public ServletConfig getServletConfig()
{
return null;
}
@Override
public String getServletInfo()
{
return null;
}
@Override
public void init(ServletConfig config) throws ServletException
{
System.out.println("servlet init()....");
}
@Override
public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException
{
System.out.println("servlet service()....");
}
}
多次运行结果
servlet init()....
servlet service()....
servlet service()....
servlet service()....
servlet service()....4、让servlet创建实例的时机提前
为了让servlet创建的时间提前，我们需要额外配置web.xml
首先创建servlet
package com.zhujunwei.servlet;
import java.io.IOException;
import javax.servlet.Servlet;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
/**
* 让servlet创建实例的时机提前
* @author Administrator
*
*/
public class HelloServlet04 implements Servlet
{
@Override
public void destroy()
{
System.out.println("Servlet04 destroy()....");
}
@Override
public ServletConfig getServletConfig()
{
return null;
}
@Override
public String getServletInfo()
{
return null;
}
@Override
public void init(ServletConfig config) throws ServletException
{
System.out.println("servlet04 init()....");
}
@Override
public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException
{
System.out.println("servlet04 service()....");
}
}
配置web.xml文件需要额外配置load-on-startup的值为2，1已经被tomcat使用了
<load-on-startup>2</load-on-startup>...
<servlet>
<servlet-name>HelloServlet04</servlet-name>
<servlet-class>com.zhujunwei.servlet.HelloServlet04</servlet-class>
<load-on-startup>2</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>HelloServlet04</servlet-name>
<url-pattern>/HelloServlet04</url-pattern>
</servlet-mapping>
</web-app>这样项目在一启动的时候就会创建该Servlet
....
十二月 25, 2018 12:01:20 下午 org.apache.catalina.core.StandardEngine startInternal
信息: Starting Servlet Engine: Apache Tomcat/9.0.8
servlet04 init()....
十二月 25, 2018 12:01:21 下午 org.apache.catalina.startup.HostConfig deployDirectory
信息: Deploying web application directory [E:\apache\Tomcat 9.0\webapps\docs]
十二月 25, 2018 12:01:21 下午 org.apache.catalina.startup.HostConfig deployDirectory
信息: Deployment of web application directory [E:\apache\Tomcat 9.0\webapps\docs] has finished in [31] ms
十二月 25, 2018 12:01:21 下午 org.apache.catalina.startup.HostConfig deployDirectory
...5、ServletConfig读取servlet配置中的信息
我们可以在servlet配置中添加一些参数，ServletConfig可以读取这些参数
servlet类的编写
package com.zhujunwei.servlet;
import java.io.IOException;
import java.util.Enumeration;
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 HelloServletConfig extends HttpServlet{
private static final long serialVersionUID = 1L;
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//ServletConfig 可以获取servlet在配置的一些信息
//1. 得到servlet配置对象 专门用于在配置servlet的信息
ServletConfig config = getServletConfig();
//获取到的是配置servlet里面servlet-name 的文本内容
String servletName = config.getServletName();
System.out.println("servletName="+servletName);
//2、。 可以获取具体的某一个参数。
String address = config.getInitParameter("address");
System.out.println("address="+address);
System.out.println("----------------------------------");
//3.获取所有的参数名称
Enumeration<String> names = config.getInitParameterNames();
//遍历取出所有的参数名称
while (names.hasMoreElements()) {
String key = (String) names.nextElement();
String value = config.getInitParameter(key);
System.out.println("key==="+key + " value="+value);
}
}
//来了post请求，就让它去执行doGet方法
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
web.xml中的配置
...
<servlet>
<servlet-name>HelloServletConfig</servlet-name>
<servlet-class>com.zhujunwei.servlet.HelloServletConfig</servlet-class>
<!-- 可以添加初始化参数 -->
<init-param>
<param-name>name</param-name>
<param-value>zhangsan</param-value>
</init-param>
<init-param>
<param-name>age</param-name>
<param-value>18</param-value>
</init-param>
<init-param>
<param-name>address</param-name>
<param-value>bejing...</param-value>
</init-param>
</servlet>
<servlet-mapping>
<servlet-name>HelloServletConfig</servlet-name>
<url-pattern>/HelloServletConfig</url-pattern>
</servlet-mapping>
</web-app>运行后得到参数的
servletName=HelloServletConfig
address=bejing...
----------------------------------
key===address value=bejing...
key===name value=zhangsan
key===age value=18
6、在项目中导入外部jar文件
在WebContent/WEB-INF下创建lib目录，将需要的jar文件直接拷贝进去即可。
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我每一次回头，都感觉自己不够努力，所以我不再回头。
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