JavaEE base (01): Servlet implementation, lifecycle execution

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A, Servlet Introduction

Server-side program written in Java, platform-independent and protocol features, the main function is to interactively browse and generate data, generate dynamic Web content. Use Servlet, can collect user input from a Web form, showing records from a database or other source, you can also create dynamic web pages.

Second, implementation

1, inherited HttpServlet

• About API

Inherited from GenericServlet comply with HTTP protocol implementation, design patterns at an angle of view, HttpServlet abstract template role as the template method: as a service () method. Basic methods: as a doPost (), doGet () methods. service () method process, part of the decision logic is omitted. This method is called seven do one or several methods, completion response to client requests. These methods do need to provide a concrete subclass of HttpServlet, the API package template method is a typical pattern.

• Code Cases

public class ServletOneImpl extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        response.setContentType("text/html;charset=utf-8");
        response.getWriter().print("执行：doGet");
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        response.setContentType("text/html;charset=utf-8");
        response.getWriter().print("执行：doPost");
    }
}

2, inherited GenericServlet

• About API

ServletConfig Servlet interface and the interface implementation class. An abstract class which service method is an abstract method.

• Code Cases

public class ServletTwoImpl extends GenericServlet {
    @Override
    public void service(ServletRequest servletRequest, ServletResponse servletResponse)
            throws ServletException, IOException {
        HttpServletResponse response = (HttpServletResponse)servletResponse ;
        response.setContentType("text/html;charset=utf-8");
        response.getWriter().print("执行：service");
    }
}

3, implement the interface Servlet

• About API

Servlet is an interface, which comprises init, getServletConfig, service, getServletInfo, destroy several core method.

• Code Cases

public class ServletThreeImpl implements Servlet {
    @Override
    public void init(ServletConfig servletConfig) throws ServletException {
        servletConfig.getServletName();
        System.out.println("init 被调用...");
    }
    @Override
    public void service(ServletRequest servletRequest, ServletResponse servletResponse)
            throws ServletException, IOException {
        System.out.println("ThreadId："+Thread.currentThread().getId());
        System.out.println("service 被调用...");
        HttpServletResponse response = (HttpServletResponse)servletResponse ;
        response.getWriter().print("Servlet.Life");
    }
    @Override
    public void destroy() {
        System.out.println("destroy 被调用...");
    }
    @Override
    public ServletConfig getServletConfig() {
        System.out.println("getServletConfig 被调用...");
        return null;
    }
    @Override
    public String getServletInfo() {
        System.out.println("getServletInfo 被调用...");
        return null;
    }
}

Third, the life cycle

• Loading and instantiation

Servlet container or when the client sends a request to start, if the Servlet container looks Servlet examples exist, if present, directly read the response request instance; if not, create a Servlet examples (of singleton design pattern). load-on-startup can be configured to create timing.

• Initialization: init ()

Instantiated, Servlet container calls the init method once and initializes the current Servlet.

• Services: service ()

After initialization, Servlet in a ready state in response to the request. Upon receiving the client request, call service () method of handling client requests, the HttpServlet's service () method will call different methods depending on the request templates.

• Destruction: destroy ()

When the Servlet container is closed, Servlet examples also destroyed at any time. You can print to see the implementation of the method by Tomcat log when you shut down the service.

Fourth, the running configuration

1, web.xml configuration

<servlet>
    <servlet-name>servletOneImpl</servlet-name>
    <servlet-class>com.node01.servlet.impl.ServletOneImpl</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>servletOneImpl</servlet-name>
    <url-pattern>/servletOneImpl</url-pattern>
</servlet-mapping>
<servlet>
    <servlet-name>servletTwoImpl</servlet-name>
    <servlet-class>com.node01.servlet.impl.ServletTwoImpl</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>servletTwoImpl</servlet-name>
    <url-pattern>/servletTwoImpl</url-pattern>
</servlet-mapping>
<servlet>
    <servlet-name>servletThreeImpl</servlet-name>
    <servlet-class>com.node01.servlet.impl.ServletThreeImpl</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>servletThreeImpl</servlet-name>
    <url-pattern>/servletThreeImpl</url-pattern>
</servlet-mapping>

Request: http://localhost:6003/servletOneImpltest.

• servlet-name: Servlet registered name.
• servlet-class: Servlet class full path name.
• serlvet-mapping: the same Servlet may be mapped to the plurality of URL.
• url-pattern: to map the path Servlet access.

2, thread pool running

Log observed above third printing Servlet implementations: Thread.currentThread().getId());.

ThreadId：32
ThreadId：33
ThreadId：32
ThreadId：31
ThreadId：32

Here difficult to find, Servlet thread pool to the modalities of implementation.

Fifth, the source code address

GitHub·地址
https://github.com/cicadasmile/java-base-parent
GitEE·地址
https://gitee.com/cicadasmile/java-base-parent