Learn to write spring boot async rest controller which support async request processing and returning the response using Callable interface.
1. spring boot async controller
Writing a controller and having it handle the request asynchronously is as simple as changing the return type of the controller’s handler method.
Given controller is simplest example and return the Callable<String> instead of normal string value "Hello World !!" after 5 seconds delay while the actual logic inside controller is accomplished.
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import java.util.concurrent.Callable;
import java.util.concurrent.ThreadLocalRandom;
@RestController
public class HelloWorldCallableController
{
@GetMapping(value = "/testCallable")
public Callable<String> echoHelloWorld()
{
return () ->
{
Thread.sleep(ThreadLocalRandom.current().nextInt(5000));
return "Hello World !!";
};
}
}
2. How to test async rest controller
To test the above controller, I am using mockito shipped with spring boot distribution.
import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.asyncDispatch;
import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.content;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.request;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.web.servlet.WebMvcTest;
import org.springframework.test.context.junit4.SpringRunner;
import org.springframework.test.web.servlet.MockMvc;
import org.springframework.test.web.servlet.MvcResult;
import org.springframework.test.web.servlet.result.MockMvcResultHandlers;
import com.howtodoinjava.springasyncexample.web.controller.HelloWorldCallableController;
@RunWith(SpringRunner.class)
@WebMvcTest(HelloWorldCallableController.class)
public class HelloWorldCallableControllerTest {
@Autowired
private MockMvc mockMvc;
@Test
public void testHelloWorldController() throws Exception
{
MvcResult mvcResult = mockMvc.perform(get("/testCallable"))
.andExpect(request().asyncStarted())
.andDo(MockMvcResultHandlers.log())
.andReturn();
mockMvc.perform(asyncDispatch(mvcResult)).andExpect(status().isOk())
.andExpect(content().contentTypeCompatibleWith("text/plain"))
.andExpect(content().string("Hello World !!"));
}
}
Program output.
2019-02-06 12:13:19.356 DEBUG 15384 --- [main] o.s.b.f.s.DefaultListableBeanFactory : Returning cached instance of singleton bean 'helloWorldCallableController' 2019-02-06 12:13:19.357 DEBUG 15384 --- [main] o.s.t.web.servlet.TestDispatcherServlet : Last-Modified value for [/testCallable] is: -1 2019-02-06 12:13:19.409 DEBUG 15384 --- [main] o.s.w.c.request.async.WebAsyncManager : Concurrent handling starting for GET [/testCallable] 2019-02-06 12:13:19.416 DEBUG 15384 --- [main] o.s.t.web.servlet.TestDispatcherServlet : Leaving response open for concurrent processing 2019-02-06 12:13:19.417 DEBUG 15384 --- [main] o.s.b.w.s.f.OrderedRequestContextFilter : Cleared thread-bound request context: org.springframework.mock.web.MockHttpServletRequest@3a627c80 2019-02-06 12:13:19.463 DEBUG 15384 --- [main] o.s.test.web.servlet.result : MvcResult details: ... 2019-02-06 12:13:24.836 DEBUG 15384 --- [mvc-task-1] o.s.w.c.request.async.WebAsyncManager : Concurrent result value [Hello World !!] - dispatching request to resume processing 2019-02-06 12:13:24.929 DEBUG 15384 --- [main] o.s.b.w.s.f.OrderedRequestContextFilter : Bound request context to thread: org.springframework.mock.web.MockHttpServletRequest@3a627c80 2019-02-06 12:13:24.929 DEBUG 15384 --- [main] o.s.t.web.servlet.TestDispatcherServlet : DispatcherServlet with name '' resumed processing GET request for [/testCallable] 2019-02-06 12:13:24.930 DEBUG 15384 --- [main] s.w.s.m.m.a.RequestMappingHandlerMapping : Looking up handler method for path /testCallable 2019-02-06 12:13:24.930 DEBUG 15384 --- [main] s.w.s.m.m.a.RequestMappingHandlerMapping : Returning handler method [public java.util.concurrent.Callable<java.lang.String> com.howtodoinjava.springasyncexample.web.controller.HelloWorldCallableController.echoHelloWorld()] 2019-02-06 12:13:24.930 DEBUG 15384 --- [main] o.s.b.f.s.DefaultListableBeanFactory : Returning cached instance of singleton bean 'helloWorldCallableController' 2019-02-06 12:13:24.930 DEBUG 15384 --- [main] o.s.t.web.servlet.TestDispatcherServlet : Last-Modified value for [/testCallable] is: -1 2019-02-06 12:13:24.931 DEBUG 15384 --- [main] s.w.s.m.m.a.RequestMappingHandlerAdapter : Found concurrent result value [Hello World !!] 2019-02-06 12:13:24.955 DEBUG 15384 --- [main] m.m.a.RequestResponseBodyMethodProcessor : Written [Hello World !!] as "text/plain" using [org.springframework.http.converter.StringHttpMessageConverter@2bffa76d] 2019-02-06 12:13:24.956 DEBUG 15384 --- [main] o.s.t.web.servlet.TestDispatcherServlet : Null ModelAndView returned to DispatcherServlet with name '': assuming HandlerAdapter completed request handling 2019-02-06 12:13:24.956 DEBUG 15384 --- [main] o.s.t.web.servlet.TestDispatcherServlet : Successfully completed request
- Notice that request handling is started on a certain thread (
main). - Another thread is doing the processing and returning the result (
mvc-task-1). - Finally, the request is dispatched to spring again to handle the result and shutting down the application (
mainandThread-2).
3. Async configuration options
To override the default async behavior such as thread pool and timeout, you can implement the WebMvcConfigurer interface and override it’s configureAsyncSupport() method.
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Bean;
import org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor;
import org.springframework.web.servlet.config.annotation.AsyncSupportConfigurer;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;
@SpringBootApplication
public class SpringAsyncExampleApplication implements WebMvcConfigurer {
public static void main(String[] args) {
SpringApplication.run(SpringAsyncExampleApplication.class, args);
}
@Override
public void configureAsyncSupport(AsyncSupportConfigurer configurer) {
configurer.setTaskExecutor(mvcTaskExecutor());
configurer.setDefaultTimeout(30_000);
}
@Bean
public ThreadPoolTaskExecutor mvcTaskExecutor() {
ThreadPoolTaskExecutor taskExecutor = new ThreadPoolTaskExecutor();
taskExecutor.setThreadNamePrefix("mvc-task-");
return taskExecutor;
}
}
4. Sourcecode files
4.1. application.properties
Enable debug logging here to understand the behavior of the application.
logging.level.org.springframework=DEBUG logging.level.com.howtodoinjava=DEBUG
4.2. pom.xml
The used pom.xml is:
<?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>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.1.2.RELEASE</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
<groupId>com.howtodoinjava.demo</groupId>
<artifactId>spring-async-demo</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>spring-async-demo</name>
<description>Demo project for Spring Boot</description>
<properties>
<java.version>1.8</java.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-webflux</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
<dependency>
<groupId>io.projectreactor</groupId>
<artifactId>reactor-test</artifactId>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build>
<repositories>
<repository>
<id>repository.spring.release</id>
<name>Spring GA Repository</name>
<url>http://repo.spring.io/release</url>
</repository>
</repositories>
</project>
Let me know if you face any error while executing this asynchronous rest service example.
Happy Learning !!
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