SpringBoot中的可快取注解

服務等級

import org.springframework.cache.annotation.Cacheable;
import org.springframework.stereotype.Service;
@Service
public class StudentService{
   
    @Cacheable(value = "student",key = "{#id,#name}")
    public Student getStudentByID(String id,String name)
    {
        return new Student(id,name ,"V");
    }
} 

執行緒示例類

 public class ThreadExample extends   Thread{

    @Autowired
    StudentService studentService;

    @Override
    public void run() {
        studentService.getStudentByID("3","f");
    }
}

我有兩個類并將執行緒啟動為：

  for (int i = 0; i < 24; i  ) {
      new ThreadExample().start();
  }

問題是可快取注解在這里不起作用，因為它不是 Spring bean 類。但是我嘗試做的事情只是執行一次具有相同 ID 和名稱的getStudentByID(String id,String name)函式。我怎么能做到這一點？你有什么主意嗎。謝謝

uj5u.com熱心網友回復：

StudentServiceThreadExample上課是因為null；

Spring僅自動裝配它創建的組件。你在打電話new ThreadExample()，Spring不知道這個物件，所以不會發生自動連接。見https://stackoverflow.com/a/42502608/2039546

根據您的用例，可能有兩種不同的方法；

• 第一個也是最快的選擇是使用建構式將服務發送到ThreadExample類。你可以很容易地做到這一點。

• 當您創建ThreadExample詢問應用程式背景關系以進行自動裝配時的其他選項。讓我舉個例子。

偽代碼將是這樣的；

@Controller
public class TestController {

    private final ApplicationContext applicationContext;

    public TestController(ApplicationContext applicationContext) {
        this.applicationContext = applicationContext;
    }

    @GetMapping(value = "/test")
    public void test() {
        ThreadExample threadExample = new ThreadExample();
        applicationContext.getAutowireCapableBeanFactory()
                .autowireBean(threadExample);
        for (int i = 0; i < 24; i  ) {
            Thread thread = new Thread(threadExample);
            thread.start();
        }
    }
}

public class ThreadExample implements Runnable {

    @Autowired
    private StudentService studentService;

    @Override
    public void run() {
        long threadId = Thread.currentThread().getId();
        String threadName = Thread.currentThread().getName();
        System.out.println(String
                .format("Thread has been called! [threadId=%s, threadName=%s]",
                        threadId, threadName));
        Student student = studentService.getStudentByID("3", "f");
        System.out.println(String
                .format("Thread has been completed. [threadId=%s, threadName=%s, studentId=%s]",
                        threadId, threadName, student.getId()));
    }
}

@Service
public class StudentService {

    @Cacheable(value = "students", key = "{#id, #name}", sync = true)
    public Student getStudentByID(String id, String name) {
        System.out.println(String
                .format("getStudentById() has been called! [id=%s, name=%s]", id, name));
        return new Student(id, name , "V");
    }
}

請注意該sync = true屬性告訴框架在計算值時阻止任何并發執行緒。這將確保在并發訪問的情況下僅呼叫一次此密集操作。

控制臺輸出為：

Thread has been called! [threadId=40, threadName=Thread-7]
Thread has been called! [threadId=41, threadName=Thread-8]
Thread has been called! [threadId=42, threadName=Thread-9]
Thread has been called! [threadId=43, threadName=Thread-10]

.
.
.
getStudentById() has been called! [id=3, name=f] <- ONLY WORKED ONCE!
Thread has been completed. [threadId=54, threadName=Thread-21, studentId=3]
Thread has been completed. [threadId=55, threadName=Thread-22, studentId=3]
Thread has been completed. [threadId=57, threadName=Thread-24, studentId=3]
Thread has been completed. [threadId=47, threadName=Thread-14, studentId=3]
Thread has been completed. [threadId=42, threadName=Thread-9, studentId=3]
.
.
.

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