Annotations simplify configuration and loading at startup

One 、 Annotations simplify configuration

Annotations are used to simplify Web Application configuration process
In the face of multiple Web Applications , If you use web.xml Heavy workload , So we can use annotations

Servlet Core notes ：@WebServlet

java page

package com.imooc.servlet;

import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet("/anno")
public class AnnotationServlet extends HttpServlet{
    

	@Override
	protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    
		resp.getWriter().println("I'm annotation servlet!");
	}
	
}

It uses @WebServlet("/anno") And in web.xml Using the following code in has the same effect

 <servlet>
  	<servlet-name>anno</servlet-name>
  	<servlet-class>com.imooc.servlet.AnnotationServlet</servlet-class>
  </servlet>
  
   <!--  take Servlet And URL binding  -->
  <servlet-mapping>
  	<servlet-name>anno</servlet-name>
  	<url-pattern>/anno</url-pattern>
  </servlet-mapping>

---

Two 、 Load on startup

• web.xml Use <load-on-startup> Set startup load
• Loading at startup is often used for system preprocessing in work

1.java page

This project is to create a database , Import and analyze

ImportServlet.java

package com.ssyt.servlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;

public class CreateServlet extends HttpServlet{
    

	@Override
	public void init() throws ServletException {
    
		System.out.println(" Creating database ");
	}
	
}

CreateServlet.java

package com.ssyt.servlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;

public class ImportServlet extends HttpServlet{
    

	@Override
	public void init() throws ServletException {
    
		System.out.println(" Importing build data ");
	}
	
}

AnalysisServlet.java

package com.ssyt.servlet;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;

@WebServlet(urlPatterns="/unused",loadOnStartup=2)
public class AnalysisServlet extends HttpServlet{
    

	@Override
	public void init() throws ServletException {
    
		System.out.println(" Analyzing results ");
	}
	
}

2.web.xml The configuration file

<servlet>
  	<servlet-name>create</servlet-name>
  	<servlet-class>com.ssyt.servlet.CreateServlet</servlet-class>
  	<load-on-startup>0</load-on-startup>
  </servlet>
   <servlet>
  	<servlet-name>import</servlet-name>
  	<servlet-class>com.ssyt.servlet.ImportServlet</servlet-class>
  	<load-on-startup>1</load-on-startup>
  </servlet>

• Among them in web.xml in ：0~9999 Indicates the sequence of loading at startup
  <load-on-startup>1</load-on-startup>
• stay java Pages use annotations to simplify configuration ： among url Must be written @WebServlet(urlPatterns="/unused",loadOnStartup=2)

3. Load on startup

No request made , Load on startup , Start in sequence