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Java登陆第二十九天——ServletConfig和ServletContext

发布时间 2023-12-23 22:31:26作者: ocraft

ServletConfig

ServletConfig是web.xml中，Servlet的初始化参数对象(每个Servlet都有一个ServletConfig对象)

web.xml

<?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">
    <!--
    每一个Servlet都可以配置多个初始化参数    
    -->
   <servlet>
       <servlet-name>Test3</servlet-name>
       <servlet-class>com.example.JavaWeb.TestServlet3</servlet-class>

        <!-- 初始化参数定义在Servlet标签之内 -->
       <init-param>
           <param-name>key</param-name>
           <param-value>value</param-value>
       </init-param>

   </servlet>
    <servlet-mapping>
        <servlet-name>Test3</servlet-name>
        <url-pattern>/Test3</url-pattern>
    </servlet-mapping>

</web-app>

查看ServletConfig源码

Servlet在初始化阶段，Tomcat会自动生成ServletConfig对象并传入init(ServletConfig config)方法

ServletConfig是一个接口

public interface ServletConfig {
    String getServletName();

    ServletContext getServletContext();

    String getInitParameter(String var1);

    Enumeration<String> getInitParameterNames();
}
方法名 描述
String getServletName() 获取Servlet名称(web.xml中servlet-name)
ServletContext getServletContext() 获取ServletContext对象(马上就介绍)
String getInitParameter(String var1) 根据初始化参数名获取值(web.xml中param-name)
Enumeration getInitParameterNames() 获取初始化参数迭代器(早期的迭代器就是Enumeration)

读取初始化参数栗子

web.xml就是上面那个

TestServlet3

public class TestServlet3 extends HttpServlet {
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletConfig servletConfig = getServletConfig();//GenericServlet类提供的方法

        Enumeration<String> es = servletConfig.getInitParameterNames();//早期的迭代器
        while (es.hasMoreElements()) {
            String s = es.nextElement();
            System.out.println("param-name："+s);
            System.out.println("param-value："+getInitParameter(s));
        }
    }
}

客户端请求URL:http://localhost:8080/JavaWeb_war_exploded/Test3

//控制台输出
param-name：key
param-value：value

在注解中设置初始化参数

TestServlet3

@WebServlet(
        urlPatterns = "/Test3",
        initParams = {@WebInitParam(name = "key",value = "value")}
)
public class TestServlet3 extends HttpServlet {
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletConfig servletConfig = getServletConfig();//GenericServlet类提供的方法

        Enumeration<String> es = servletConfig.getInitParameterNames();//早期的迭代器
        while (es.hasMoreElements()) {
            String s = es.nextElement();
            System.out.println("param-name："+s);
            System.out.println("param-value："+getInitParameter(s));
        }
    }
}

客户端请求URL:http://localhost:8080/JavaWeb_war_exploded/Test3

//控制台输出
param-name：key
param-value：value

ServletContext

  • ServletContext是web.xml中，项目的初始化参数对象(每个项目仅有一个初始化参数对象)

  • ServletConfig是web.xml中，Servlet的初始化参数对象(每个Servlet都有一个ServletConfig对象)

image

web.xml

<?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">
    <context-param>
        <param-name>key</param-name>
        <param-value>value</param-value>
    </context-param>
</web-app>

可以通过ServletConfig的getServletContext()方法获取ServletContext

@WebServlet(
        urlPatterns = "/Test3",
        initParams = {@WebInitParam(name = "key",value = "value")}
)
public class TestServlet3 extends HttpServlet {
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletConfig servletConfig = getServletConfig();//GenericServlet类提供的方法

        Enumeration<String> es = servletConfig.getInitParameterNames();//早期的迭代器
        while (es.hasMoreElements()) {
            String s = es.nextElement();
            System.out.println("param-name："+s);
            System.out.println("param-value："+getInitParameter(s));
        }

        System.out.println("==============================");
        ServletContext servletContext = getServletConfig().getServletContext();
        Enumeration<String> ess = servletContext.getInitParameterNames();
        while (ess.hasMoreElements()) {
            String s = ess.nextElement();
            System.out.println("context-name："+s);
            System.out.println("context-value："+getInitParameter(s));
        }
    }
}

客户端请求URL:http://localhost:8080/JavaWeb_war_exploded/Test3

//控制台输出
param-name：key
param-value：value
==============================
context-name：key
context-value：value