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1、 Write a class to inherit HttpServlet class
2、 Rewrite according to business needs doGet or doPost Method
3、 To web.xml Middle configuration Servlet Program

1、 Write a class ,Alt+insert Some methods needed in shortcut key rewriting

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import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import java.io.IOException;public class HelloServlet2 extends HttpServlet {    @Override    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {       // super.doGet(req, resp);        System.out.println("HelloServlet2 Of  get request ");    }    @Override    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {      //  super.doPost(req, resp);        System.out.println("HelloServlet2 Of  post request ");    }}

To web.xml Configure the access path in the file

    <servlet>        <servlet-name>HelloServlet2</servlet-name>        <servlet-class>com.servlet.HelloServlet2</servlet-class>    </servlet>    <servlet-mapping>        <servlet-name>HelloServlet2</servlet-name>        <url-pattern>/hello2</url-pattern>    </servlet-mapping>

The access address in the form hello Change for hello2

Run after submission ：

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Use idea establish Servlet Program

Select the package to implement →Servlet Program

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Configuration information

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Check with 3.0 The annotation configuration of

Only need web.xml Add a path to the （ Others have been generated automatically ）

    <servlet-mapping>        <servlet-name>HelloServlet3</servlet-name>        <url-pattern>/hello3</url-pattern>    </servlet-mapping>

Servlet Inheritance system

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doGet and dopost Source code

    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {        String msg = lStrings.getString("http.method_get_not_supported");        this.sendMethodNotAllowed(req, resp, msg);    }

    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {        String msg = lStrings.getString("http.method_post_not_supported");        this.sendMethodNotAllowed(req, resp, msg);    }

servlet Method part source code

 protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {        String method = req.getMethod();        long lastModified;        if (method.equals("GET")) {            lastModified = this.getLastModified(req);            if (lastModified == -1L) {                this.doGet(req, resp);            } else {                long ifModifiedSince;                try {                    ifModifiedSince = req.getDateHeader("If-Modified-Since");                } catch (IllegalArgumentException var9) {                    ifModifiedSince = -1L;                }                if (ifModifiedSince < lastModified / 1000L * 1000L) {                    this.maybeSetLastModified(resp, lastModified);                    this.doGet(req, resp);                } else {                    resp.setStatus(304);                }            }        }

ServletConfig class

ServletConfig yes Servlet Program configuration information class .
Servlet Procedure and ServletConfig All objects have Tomcat Responsible for creating , We are responsible for using .
Servlet By default, the program is created during one access ,ServletConfig Is each Servlet When the program is created , Just create a corresponding ServletConfig object

ServletConfig The three functions of classes

1、 Can get Servlet Program alias （servlet-name Value ）

2、 Get initialization parameters init-param

3、 obtain ServletContent object

Location init Method

1、 obtain servlet Alias

  public void init(ServletConfig servletConfig) throws ServletException {         System.out.println("HelloServlet  Its alias is "+servletConfig.getServletName());   }

2、 Get initialization parameters init-param, Thanks for the others in front

Now? web.xml In the document with <init-param>

<!--servlet Label to Tomcat To configure Servlet Program -->    <servlet>        <!-- servlet-name to Servlet The program has an alias ( The general alias is called the class name )-->        <servlet-name>HelloServlet</servlet-name>        <!--servlet-class yes Servlet The full class name of the program  -->        <servlet-class>com.servlet.HelloServlet</servlet-class>        <!--init-param Initialization parameters , This is a key value pair. You can write many pairs  -->        <init-param>            <!--  Parameter name -->            <param-name>username</param-name>            <!-- Is the value of the parameter  -->            <param-value>root</param-value>        </init-param>        <init-param>        <!--  Parameter name -->        <param-name>url</param-name>        <!-- Is the value of the parameter  -->        <param-value>jdbc:mysql://localhost:3306/text</param-value>        </init-param>    </servlet>

In the realization of Servlet Interface class init() Next

  // 2、 Get initialization parameters init-param        System.out.println(" Initialize parameters username The value of is "+servletConfig.getInitParameter("username"));        System.out.println(" Initialize parameters url The value of is "+servletConfig.getInitParameter("url"));

3、 obtain ServlertContent object

 // 3、 obtain ServletContent object         System.out.println("servletcontent The object is "+servletConfig.getServletContext());

The above operation results ：

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every last ServletConfig Program independence , stay web.xml Information in each class in is not shared ,

rewrite init Methods should be added super.init(config), Have to access the parent class init Initialization method , Otherwise, the report will be wrong

The inheritance system can tell ServletConfig stay GenericServlet Class , In this category init Definition ：

    public void init(ServletConfig config) throws ServletException {        this.config = config;        this.init();    }

So if you rewrite init Method , Have to add super.init(config), Otherwise, the father of init Method will not execute ( The save operation in the parent class cannot be performed )

ServletContext class

What is? ServletContext？

1、ServletContent It's an interface , He said Servlet Context object

2、 One web engineering , only one ServletContext Object instances .

3、ServletContent Object is a domain object .

4、 stay web Create after the project starts , stay web Destroy after the completion of the project

What is domain object ？

Domain object , It can be like Map The same object that accesses data , It's called a domain object .
The domain here refers to the operating range of accessing data .

Comparison diagram ：

	Save the data	Take the data	Delete data
Map	put()	get()	remove()
Domain object	setAttribute()	getAttribute()	removeAttribute()

ServletContext The four functions of a class

1、 obtain web.xml Context parameters of the configuration in context-param

2、 Get the current project path you , Format ：/ Project path

3、 Get the absolute path on the server hard disk after deployment

4、 image Map And access data

Create a class with a shortcut ContextServlet, stay web.xml Configuration path ( The rest have been automatically generated )

    <servlet>        <servlet-name>ContextServlet</servlet-name>        <servlet-class>com.servlet.ContextServlet</servlet-class>    </servlet><!--  The above automatically generates , Next, write your own path -->    <servlet-mapping>        <servlet-name>ContextServlet</servlet-name>        <url-pattern>/contextServlet</url-pattern>    </servlet-mapping>

1、 obtain web.xml Context parameters of the configuration in ,

First of all have to in web.xml Middle configuration context-param( Usually written in other servlet above )

<!--context-param Is the context parameter （ He belongs to the whole web engineering ）-->    <context-param>        <!-- Parameter name  -->        <param-name>username</param-name>        <!-- Parameter values -->        <param-value>context</param-value>    </context-param><!-- You can write multiple pairs of context parameters -->    <context-param>        <param-name>password</param-name>        <param-value>root</param-value>    </context-param>

stay ContextServlet Class doGet() Method in

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {        //1、 obtain web.xml Context parameters of the configuration in context-param        // Get objects         ServletContext context = getServletConfig().getServletContext();        String username = context.getInitParameter("username");        String password = context.getInitParameter("password");        System.out.println("context-param Parameters username The value of is "+username);        System.out.println("context-param Parameters password The value of is "+password);    }}

After running, the result is ：

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It's easy to get wrong ：

①： In the configuration web.xml In the address in the file / Don't forget the diagonal pole , Otherwise, the address will be invalid

 <url-pattern>/contextServlet</url-pattern>

②： Getting parameters in a class should be in doGet() Writing in method , Otherwise, the access address will not display the corresponding information after running

Get the current project path

     System.out.println(" Current engineering path ："+context.getContextPath());

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Get the absolute path on the server hard disk after deployment

System.out.println(" Get the path of project deployment "+context.getRealPath("/"));

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This diagonal bar / Indicates the path to the current project

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map And access data

Create a Servlet class , stay web.xml Configure the path in the file

   <servlet>        <servlet-name>ContextServlet1</servlet-name>        <servlet-class>com.servlet.ContextServlet1</servlet-class>    </servlet><!--  The above is automatically configured -->  <servlet-mapping>        <servlet-name>ContextServlet1</servlet-name>        <url-pattern>/contextServlet1</url-pattern>    </servlet-mapping>

In class ：

public class ContextServlet1 extends HttpServlet {    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {         // obtain ServletContext object         ServletContext context = getServletContext();        System.out.println(" Before saving Context obtain key1 The value of is ："+context.getAttribute("key1"));        context.setAttribute("key1","value1");        System.out.println("context get data key1 The value of is ："+context.getAttribute("key1"));    }}

We can directly use getServletContext() Get objects , It's simpler , without getServletConfig().getServletContext();

We ctrl+b Look at the source ：

    public ServletContext getServletContext() {        return this.getServletConfig().getServletContext();    }

The source code has done that step , So we can go back directly .

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We continue to define a class called ContextServlet2

public class ContextServlet2 extends HttpServlet {    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {        ServletContext context = getServletContext();        System.out.println("ContextServlet2 in  context get data key1 The value of is ："+context.getAttribute("key1"));    }}

Deployment is omitted , After running

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It's not hard to find out when ContextServlet1 There is data stored in ,ContextServlet2 The data can be found in . It's fine too context The data under is shared data

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