Seven Common Spring Boot Performance Optimization Techniques

Hello everyone, I am Chen. This article introduces seven common Spring Boot performance optimization directions.

1. Asynchronous Execution

Two implementation methods are provided:

Use the asynchronous annotation @Async and add @EnableAsync to the startup class.

Leverage JDK 8's CompletableFuture class.

Example using a custom thread with CompletableFuture:

@AllArgsConstructor
public class AskThread implements Runnable {
    private CompletableFuture<Integer> re = null;
    public void run() {
        int myRe = 0;
        try {
            myRe = re.get() * re.get();
        } catch (Exception e) {
            e.printStackTrace();
        }
        System.out.println(myRe);
    }
    public static void main(String[] args) throws InterruptedException {
        final CompletableFuture<Integer> future = new CompletableFuture<>();
        new Thread(new AskThread(future)).start();
        Thread.sleep(1000);
        future.complete(60);
    }
}

In this example, the AskThread starts before its data is ready, causing the call to myRe = re.get() * re.get() to block. After a simulated 1‑second delay, the result is supplied to the future, allowing the thread to continue.

Another example demonstrates CompletableFuture.supplyAsync to run a slow calc() method in a new thread while immediately returning a CompletableFuture that later provides the result:

public class Calc {
    public static Integer calc(Integer para) {
        try { Thread.sleep(1000); } catch (InterruptedException e) { e.printStackTrace(); }
        return para * para;
    }
    public static void main(String[] args) throws ExecutionException, InterruptedException {
        final CompletableFuture<Void> future = CompletableFuture.supplyAsync(() -> calc(50))
            .thenApply(i -> Integer.toString(i))
            .thenApply(str -> "\"" + str + "\"")
            .thenAccept(System.out::println);
        future.get();
    }
}

The supplyAsync method creates a CompletableFuture that runs calc() in a new thread, returning immediately. The future acts as a contract for obtaining the eventual result.

When a controller method returns a Callable, Spring MVC dispatches it to a TaskExecutor for asynchronous processing, keeping the response open until the callable completes.

@RestController
public class HelloController {
    private static final Logger logger = LoggerFactory.getLogger(HelloController.class);
    @Autowired private HelloService hello;
    @GetMapping("/helloworld")
    public String helloWorldController() { return hello.sayHello(); }
    @GetMapping("/hello")
    public Callable<String> helloController() {
        logger.info(Thread.currentThread().getName() + " entering helloController");
        Callable<String> callable = new Callable<String>() {
            @Override public String call() throws Exception {
                logger.info(Thread.currentThread().getName() + " entering call");
                String say = hello.sayHello();
                logger.info(Thread.currentThread().getName() + " from helloService");
                return say;
            }
        };
        logger.info(Thread.currentThread().getName() + " returning from helloController");
        return callable;
    }
}

Asynchronous calls can also be handled with WebAsyncTask, allowing custom timeout handling:

@RestController
public class HelloController {
    private static final Logger logger = LoggerFactory.getLogger(HelloController.class);
    @Autowired private HelloService hello;
    @GetMapping("/world")
    public WebAsyncTask<String> worldController() {
        logger.info(Thread.currentThread().getName() + " entering helloController");
        WebAsyncTask<String> webAsyncTask = new WebAsyncTask<>(3000, new Callable<String>() {
            @Override public String call() throws Exception {
                logger.info(Thread.currentThread().getName() + " entering call");
                String say = hello.sayHello();
                logger.info(Thread.currentThread().getName() + " from helloService");
                return say;
            }
        });
        webAsyncTask.onCompletion(() -> logger.info(Thread.currentThread().getName() + " completed"));
        webAsyncTask.onTimeout(() -> { logger.info(Thread.currentThread().getName() + " onTimeout"); throw new TimeoutException("call timeout"); });
        return webAsyncTask;
    }
    @GetMapping("/exception")
    public WebAsyncTask<String> exceptionController() {
        Callable<String> callable = () -> { logger.info(Thread.currentThread().getName() + " entering call"); throw new TimeoutException("call timeout!"); };
        return new WebAsyncTask<>(20000, callable);
    }
}

2. Increase Embedded Tomcat Maximum Connections

Configuration example to raise connection and thread limits:

@Configuration
public class TomcatConfig {
    @Bean
    public ConfigurableServletWebServerFactory webServerFactory() {
        TomcatServletWebServerFactory tomcatFactory = new TomcatServletWebServerFactory();
        tomcatFactory.addConnectorCustomizers(new MyTomcatConnectorCustomizer());
        tomcatFactory.setPort(8005);
        tomcatFactory.setContextPath("/api-g");
        return tomcatFactory;
    }
    class MyTomcatConnectorCustomizer implements TomcatConnectorCustomizer {
        @Override public void customize(Connector connector) {
            Http11NioProtocol protocol = (Http11NioProtocol) connector.getProtocolHandler();
            protocol.setMaxConnections(20000);
            protocol.setMaxThreads(2000);
            protocol.setConnectionTimeout(30000);
        }
    }
}

3. Use @ComponentScan()

Applying @ComponentScan() can scan packages faster than the default @SpringBootApplication annotation.

4. Switch Default Tomcat Container to Undertow

Replace the Tomcat starter with Undertow in Maven:

<exclusions>
    <exclusion>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-tomcat</artifactId>
    </exclusion>
</exclusions>

Change to:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-undertow</artifactId>
</dependency>

5. Use BufferedWriter for Buffering

Encourage using BufferedWriter to improve I/O efficiency (code omitted for brevity).

6. DeferredResult for Asynchronous Calls

@RestController
public class AsyncDeferredController {
    private final Logger logger = LoggerFactory.getLogger(this.getClass());
    private final LongTimeTask taskService;
    @Autowired public AsyncDeferredController(LongTimeTask taskService) { this.taskService = taskService; }
    @GetMapping("/deferred")
    public DeferredResult<String> executeSlowTask() {
        logger.info(Thread.currentThread().getName() + " entering executeSlowTask");
        DeferredResult<String> deferredResult = new DeferredResult<>();
        taskService.execute(deferredResult);
        logger.info(Thread.currentThread().getName() + " returning from executeSlowTask");
        deferredResult.onTimeout(() -> { logger.info(Thread.currentThread().getName() + " onTimeout"); deferredResult.setErrorResult("time out!"); });
        deferredResult.onCompletion(() -> logger.info(Thread.currentThread().getName() + " onCompletion"));
        return deferredResult;
    }
}

7. AsyncHandlerInterceptor for Intercepting Asynchronous Calls

@Component
public class MyAsyncHandlerInterceptor implements AsyncHandlerInterceptor {
    private static final Logger logger = LoggerFactory.getLogger(MyAsyncHandlerInterceptor.class);
    @Override public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception { return true; }
    @Override public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
        logger.info(Thread.currentThread().getName() + " service completed, returning result to client");
    }
    @Override public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        if (ex != null) { System.out.println("Exception occurred:" + ex.getMessage()); }
    }
    @Override public void afterConcurrentHandlingStarted(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        String resp = "my name is chhliu!";
        response.setContentLength(resp.length());
        response.getOutputStream().write(resp.getBytes());
        logger.info(Thread.currentThread().getName() + " entering afterConcurrentHandlingStarted");
    }
}

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