Asynchronous Spring MVC – Hello World Example

Asynchronous processing is supported since Servlet 3.0. Spring MVC makes asynchronous processing even simpler. Here is a hello world level demo on how to do that using Spring MVC.

Basically there are 2 things need to do:

1. configure web.xml to turn on async support
2. return Callable instance  instead of what you mostly return, String/Model/ModelAndView  etc, from a controller’s method.

Let’s suppose you know how to setup a maven managed Spring MVC project in Eclipse. If you don’t , here is the tutorial

0. What you need

JDK 1.7+

Maven 3.2.1

1. Maven  pom.xml

<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/maven-v4_0_0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.shengwang.demo</groupId>
  <artifactId>spring-mvc-asynchronous-basic</artifactId>
  <packaging>war</packaging>
  <version>1.0</version>
  <name>spring-mvc-asynchronous-basic Maven Webapp</name>
  <url>http://maven.apache.org</url>

  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <spring-framework.version>4.1.6.RELEASE</spring-framework.version>

    <!-- Logging -->
    <logback.version>1.1.2</logback.version>
    <slf4j.version>1.7.7</slf4j.version>
  </properties>
  
  <dependencies>
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-webmvc</artifactId>
      <version>${spring-framework.version}</version>
    </dependency>

    <!-- Logging with SLF4J & LogBack -->
    <dependency>
      <groupId>org.slf4j</groupId>
      <artifactId>slf4j-api</artifactId>
      <version>${slf4j.version}</version>
      <scope>compile</scope>
    </dependency>
    <dependency>
      <groupId>org.slf4j</groupId>
      <artifactId>jcl-over-slf4j</artifactId>
      <version>${slf4j.version}</version>
      <scope>compile</scope>
    </dependency>
    <dependency>
      <groupId>ch.qos.logback</groupId>
      <artifactId>logback-classic</artifactId>
      <version>${logback.version}</version>
      <scope>runtime</scope>
    </dependency>
  </dependencies>

  <build>
    <finalName>spring-mvc-asynchronous-basic</finalName>
    <!-- Use Java 1.7 -->
    <plugins>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-compiler-plugin</artifactId>
        <version>2.5.1</version>
        <configuration>
          <source>1.7</source>
          <target>1.7</target>
        </configuration>
      </plugin>
    </plugins>
  </build>
</project>

In maven pom.xml, dependencies like Spring MVC and logging has been added. Also JDK version is set to 1.7

2. configure web.xml to support async

Use <async-supported>true</async-supported> to turn on async support for servlets and filters. Use <dispatcher>ASYNC</dispatcher> for filter-mapping  if any.

<web-app xmlns="http://java.sun.com/xml/ns/javaee" 
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 
        http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
  version="3.0">
  <display-name>Demo for mvc hello world config</display-name>
  

  <servlet>
    <servlet-name>dispatcher</servlet-name>
    <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
    <load-on-startup>1</load-on-startup>
    <!-- turn on async support for servlet -->
    <async-supported>true</async-supported>
  </servlet>
  <servlet-mapping>
    <servlet-name>dispatcher</servlet-name>
    <url-pattern>/</url-pattern>
  </servlet-mapping>
  
</web-app>

3. Define java class

First is the service class, just sleep 3 seconds to mimic a slow task.

package com.shengwang.demo;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.stereotype.Service;

@Service
public class HelloService {
  Logger logger = LoggerFactory.getLogger(HelloService.class);
  
  public String doSlowWork() {
    logger.info("Start  slow work");
    try {
      Thread.sleep(3000);
    } catch (InterruptedException e) {
      e.printStackTrace();
    }
    logger.info("finish slow work");
//    return "forward:/another";  // forward to another url
    return "index";       // return view's name
  }
}

The hello service does nothing except sleep a few seconds then return view's name.

The controller look like below.

package com.shengwang.demo;

import java.util.concurrent.Callable;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;


@Controller
public class HelloController {
  Logger logger = LoggerFactory.getLogger(HelloController.class);

  @Autowired
  HelloService helloService;

  @RequestMapping("/helloAsync")
  public Callable<String> sayHelloAsync() {
    logger.info("Entering controller");

    Callable<String> asyncTask = new Callable<String>() {

      @Override
      public String call() throws Exception {
        return helloService.doSlowWork();
      }
    };
    
    logger.info("Leaving  controller");
    return asyncTask;
  }
}

The method sayHelloAsync return a Callable instance.

4. Configure Spring MVC

Compare to the basic hello world Spring mvc configuration in tutorial on “How to setup Spring MVC project with maven in Eclipse”, the difference is the task executor setup for async tasks.

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xmlns:beans="http://www.springframework.org/schema/beans"
  xmlns:context="http://www.springframework.org/schema/context"
  xmlns:mvc="http://www.springframework.org/schema/mvc"
  xsi:schemaLocation="
    http://www.springframework.org/schema/beans 
    http://www.springframework.org/schema/beans/spring-beans.xsd 
    http://www.springframework.org/schema/context 
    http://www.springframework.org/schema/context/spring-context.xsd
    http://www.springframework.org/schema/mvc
    http://www.springframework.org/schema/mvc/spring-mvc.xsd">
     
  <context:component-scan base-package="com.shengwang.demo" />
  
  <!-- ================================== -->   
  <!-- 0. Set up task executor for async  -->
  <!-- ================================== -->
  <mvc:annotation-driven> 
    <mvc:async-support default-timeout="30000" task-executor="taskExecutor"/>
  </mvc:annotation-driven>
  <!-- modify the parameters of thread pool -->
  <bean id="taskExecutor" class="org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor">
    <property name="corePoolSize" value="5"/>
    <property name="maxPoolSize" value="50"/>
    <property name="queueCapacity" value="10"/>
    <property name="keepAliveSeconds" value="120"/>
  </bean>
   
  <!-- ================================== -->
  <!-- 1. mapping static resources        -->
  <!-- ================================== -->
  <mvc:resources location="/static-resources/css/" mapping="/css/**" cache-period="3600"/>
  <mvc:resources location="/static-resources/img/" mapping="/img/**" cache-period="3600"/>
  <mvc:resources location="/static-resources/js/" mapping="/js/**" cache-period="3600"/>
   
   
  <!-- ================================== -->
  <!--  2. view resolver for JSP          -->
  <!-- ================================== -->
  <bean id="viewResolver"
    class="org.springframework.web.servlet.view.InternalResourceViewResolver">
    <property name="prefix" value="/WEB-INF/"/>
    <property name="suffix" value=".jsp"/>
  </bean>
</beans>

In real project, the task executor must be explicitly setup instead of using the default SimpleAsyncTaskExecutor, which can not be used in production. As Spring document says:

It is highly recommended to configure this property since by default Spring MVC uses SimpleAsyncTaskExecutor.

5. Run the async web app

Run the project and access http://localhost:8080/spring-mvc-asynchronous-basic/helloAsync, the log from console looks like below

The controller thread(http-bio-8080-exec-7) exits immediately, but another MVC mangaged thread(taskExecutor-1) takes 3 seconds to finish the slow work. Although the controller thread finishes very fast, the connection keeps open, browser doesn’t get response until 3 seconds later, all threads finish.