Servlet源码初探

Posted 2020-08-27 no-npe

　　年底，公司的事情告一段落，就来捣鼓一下这个Servlet源码，为下一步的spingmvc源码初探做准备

1、Servlet接口

public interface Servlet {

    void init(ServletConfig var1) throws ServletException;

    ServletConfig getServletConfig();

    void service(ServletRequest var1, ServletResponse var2) throws ServletException, IOException;

    String getServletInfo();

    void destroy();
}

2、ServletConfig接口

public interface ServletConfig {

    String getServletName();

    ServletContext getServletContext();

    String getInitParameter(String var1);

    Enumeration<String> getInitParameterNames();
}

3、抽象类GenericServlet

public abstract class GenericServlet implements Servlet, ServletConfig, Serializable{
	.
	.
	.
	.
　　public String getInitParameter(String name) {
        ServletConfig sc = this.getServletConfig();
        if(sc == null) {
            throw new IllegalStateException(lStrings.getString("err.servlet_config_not_initialized"));
        } else {
            return sc.getInitParameter(name);
        }
    }

　　public ServletConfig getServletConfig() {
        return this.config;
    }

    public ServletContext getServletContext() {
        ServletConfig sc = this.getServletConfig();
        if(sc == null) {
            throw new IllegalStateException(lStrings.getString("err.servlet_config_not_initialized"));
        } else {
            return sc.getServletContext();
        }
    }
} 

4、抽象类HttpServlet 

public abstract class HttpServlet extends GenericServlet {
                ......
}            

5、解释

　　一个servlet对应一个ServletConfig，该接口由容器实现，比如Tomcat，封装了servlet的初始化信息，每一个ServletConfig中有一个获取ServletContext引用的方法，而一个web应用的所有Servlet共享同一个ServletContext所以该对象被称为application对象，我们在web项目中新建的一个servlet只需继承自抽象类HttpServlet就可以调用this.getServletConfig().getInitParameter(String name)和this.getServletContext().getInitParameter(String name)这两个方法，这两个方法获取值的区别：

1、this.getServletConfig().getInitParameter(String name)

<!-- Spring MVC配置 -->
<servlet>
   <servlet-name>spring</servlet-name>
   <servlet-class>
      org.springframework.web.servlet.DispatcherServlet
   </servlet-class>
   <init-param>
         <param-name>contextConfigLocation</param-name>
         <param-value>classpath:spring-servlet.xml</param-value>
   </init-param>
   <load-on-startup>1</load-on-startup>
</servlet>

2、this.getServletContext().getInitParameter(String name)

<context-param>
　　<param-name>contextConfigLocation</param-name>
　　<param-value>classpath:spring-context.xml</param-value>
</context-param>

　　这两个参数是Springmvc配置的基本参数。