this is a minimal style tutorial to connnect the concepts of Java, to servlets, then to spring framework

1. servlet

tutorial

• you need: Java, tomcat
• you create two files:
• HelloWorld.java
• web.xml

HelloWorld.java

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;

public class HelloWorld extends HttpServlet {

  public void doGet(HttpServletRequest request,
                    HttpServletResponse response)
            throws ServletException, IOException
  {
      PrintWriter out = response.getWriter();
      out.println("Hello, World!");
  }
}

web.xml

<?xml version="1.0" ?>
<web-app>

<servlet>
   <servlet-name>C6376Servlet</servlet-name>
   <servlet-class>HelloWorld</servlet-class>
</servlet>

<servlet-mapping>
   <servlet-name>C6376Servlet</servlet-name>
   <url-pattern>/ZhouURL</url-pattern>
</servlet-mapping>

</web-app>

• build and deploy:

javac HellowWorld.java -cp $CATALINA_HOME/lib/servlet-api.jar
cp HellowWorld.class $CATALINA_HOME/webapps/ROOT/WEB-INF/classes/
cp web.xml $CATALINA_HOME/webapps/ROOT/WEB-INF/

notes:

• compare with a vanilla HelloWorld Java program, a servlet is (1) an object living in the enrivoment of servlet container, e.g. a tomcat; (2) responsible of answering HTTP requests sent to a certain URL
• the example thus inclues two files: one defines the servelt; the other says which request to respond

references:

1. servlets - first example
2. The Deployment Descriptor: web.xml

2. Spring - doing the same thing with Spring MVC and Spring Boot

tutorial

• you need Java, maven
• you create two files
• src/main/java/hello/HelloController.java
• pom.xml

src/main/java/hello/HellowController.java

package hello;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.boot.*;
import org.springframework.boot.autoconfigure.*;
import org.springframework.web.bind.annotation.*;

@RestController
@SpringBootApplication
public class HelloController {
    @RequestMapping("/")
    String home() {
        return "Hello World!";
    }
    public static void main(String[] args) throws Exception {
        SpringApplication.run(HelloController.class, args);
    }
}

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>hello</groupId>
    <artifactId>SpringBootSampleWeb</artifactId>
    <version>0.0.1</version>

    <properties>
        <!-- The main class to start by executing java -jar -->
        <start-class>hello.HelloController</start-class>
    </properties>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.5.2.RELEASE</version>
    </parent>
    <!-- Additional lines to be added here... -->
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
    </dependencies>
    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>
</project>

• build and run

mvn package
java -jar target/SpringBootSampleWeb-0.0.1.jar

notes

• it responds at the root URL ('/')
• strictly speaking, package is not required for a 'minimal' example, but it is a good habit in my opinion.
• Spring framework can work as a general 'container' of objects; Boot works as a actual servlet container on top of being a general conceptual container.

references

1. Spring Boot Quick Start note how SpringBootApplication and RestController are two separate classes
2. 'official' Spring Boot tutorial this is not much more than the 'minimal' one, but explains better how it works

3. View - using Spring view with a proper template

tutorial

• you need Java, maven
• create 4 files: 2 Java, 1 HTML, 1 xml
• src/main/java/hello/GreetingController.java
• src/main/java/hello/Application.java
• src/main/resources/templates/greeting.html
• pom.xml

src/main/java/hello/GreetingController.java

package hello;

import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;

@Controller
public class GreetingController {

    @RequestMapping("/greeting")
    public String greeting(@RequestParam(value="name", required=false, defaultValue="World") String name, Model model) {
        model.addAttribute("name", name);
        return "greeting";
    }

}

src/main/java/hello/Application.java

package hello;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class Application {

    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }

}

src/main/resources/templates/greeting.html

<!DOCTYPE HTML>
<html xmlns:th="http://www.thymeleaf.org">
<head>
    <title>Getting Started: Serving Web Content</title>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
</head>
<body>
    <p th:text="'Hello, ' + ${name} + '!'" />
</body>
</html>

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>org.springframework</groupId>
    <artifactId>gs-serving-web-content</artifactId>
    <version>0.1.0</version>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.5.2.RELEASE</version>
    </parent>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-thymeleaf</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
            <optional>true</optional>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

• build and run

mvn package
java -jar target/gs-serving-web-content-0.1.0.jar

notes

• maven must be version 3 (or newer I guess)
• it is accessed from /greeting URL, or /greeting?name=Joe. nothing on the rool URL
• greeting.html serves as a 'template'. thymeleaf is used as the the template technology in the original example. you can use other templates, e.g. JSP.
• one of the magics done by Boot: 'if Thymeleaf is on your path, Spring Boot adds a SpringTemplateEngine to your application context automatically'
• Converting a Spring Boot JAR Application to a WAR
• it helps to understand what Spring Boot Maven plugin does (e.g. creating the 'über-jar' file).

refernces

1. Serving Web Content with Spring MVC
2. compare with legacyrest from the microservice book. legacyrest has a lot of more stuff. I am not sure whether they are useful or relavent. But it is similar to these examples.