Understanding @Autowired vs @Resource and Injection Methods in Spring

In this article, a senior architect discusses common pitfalls when using Spring's @Autowired injection, including Java class initialization order and the strong coupling introduced by @Autowired compared to the standard @Resource annotation.

The author explains that @Autowired injection occurs after the subclass constructor, which can lead to NullPointerException if beans are not properly initialized, and highlights that @Resource is a JSR‑250 standard that does not produce warnings, making it more portable across IoC frameworks.

Various injection approaches are presented: field injection using @Autowired , setter injection, constructor injection, and a simplified constructor injection using Lombok's @RequiredArgsConstructor . Code examples for each method are provided.

@RestController
public class TestController2 {
    ITestService testService;
    /* 基于set注入 */
    @Autowired
    public void setTestService(ITestService iTestService) {
        this.testService = iTestService;
    }
    @GetMapping("/status2")
    public Result
status() {
        return testService.status();
    }
}

@RestController
public class TestController1 {
    ITestService testService;
    /* 基于构造方法的注入 */
    public TestController1(ITestService iTestService) {
        this.testService = iTestService;
    }
    @GetMapping("/status1")
    public Result
status() {
        return testService.status();
    }
}

<dependency>
    <groupId>org.projectlombok</groupId>
    <artifactId>lombok</artifactId>
    <version>1.18.2</version>
</dependency>

@RestController
@RequiredArgsConstructor
public class TestController3 {
    private final ITestService testService;
    @GetMapping("/status3")
    public Result
status() {
        return testService.status();
    }
}

Constructor injection is recommended as it avoids circular dependencies and, when combined with Lombok, reduces boilerplate code.

The article concludes that using constructor injection, possibly with Lombok, offers a balanced solution between simplicity and loose coupling.