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Spring IoC注解配置之Autowired和Resource注解
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1 Autowired注解

在cn.tedu.annotationioc.beans包中添加Subject类：

@Component(value = "subject") ---------
public class Subject {                 |
    private String name = "Java";      |
                                       |
    public String getName() {          |
        return name;                   |
    }                                  |
                                       |
    public void setName(String name) { |
        this.name = name;              |
    }                                  |
                                       |自
    @Override                          |动
    public String toString() {         |装
        return "Subject{" +            |配
            "name='" + name + '\'' +   |
            '}';                       |
    }                                  |
}                                      |
                                       |
修改Student：                          |
                                       |
@Component(value = "student")          |
public class Student {                 |
    ...                                |
    @Autowired                         |
    private Subject subject; <---------
    ...
    public Subject getSubject() {
        return subject;
    }

    public void setSubject(Subject subject) {
        this.subject = subject;
    }
    ...
    @Override
    public String toString() {
        return "Student{" +
            "number='" + number + '\'' +
            ", name='" + name + '\'' +
            ", gender='" + gender + '\'' +
            ", age=" + age +
            ", enrollment=" + enrollment +
            ", subject=" + subject +
            '}';
    }
    ...
}

测试：

public class SpringTest {
    public static void main(String[] args) {
        ClassPathXmlApplicationContext context =
            new ClassPathXmlApplicationContext("applicationContext.xml");
        Student student = context.getBean("student", Student.class);
        System.out.println(student);
    }
}

Student{number='1001', name='张飞', gender='男', age=20, enrollment=Mon Feb 14 10:23:50 CST 2022, subject=Subject{name='Java'}}

Autowired注解用于声明此属性自动装配，相当于bean标签的autowire属性：

- 按类型匹配，无匹配或多匹配则抛出异常
- required=false，无匹配或多匹配则放弃装配，不抛出异常，属性取null

Autowired注解也可以用在Set方法上：

@Component(value = "student")
public class Student {
    ...

    private Subject subject;

    ...

    @Autowired
    public void setSubject(Subject subject) {
        this.subject = subject;
    }

    ...
}

这时可以结合使用Qualifier注解：

@Component(value = "student")
public class Student {
    ...

    private Subject subject;

    ...

    @Autowired
    public void setSubject(@Qualifier("subject") Subject subject) {
        this.subject = subject;
    }

    ...
}

可以在Qualifier注解的参数中指定注入源的名字，若类型不一致则抛出异常。

例程：AnnotationIoC

2 Resource注解

public class Student {
    ...
    @Resource
    private Subject subject;
    ...
}

Resource注解并非由Spring提供，而是源自J2EE，依赖于“Javax Annotation API”。其功能与Autowired注解类似，但不完全相同：

- 优先按名字匹配，名字匹配但类型不匹配则抛出异常
- 没有名字匹配的，再按类型匹配，无匹配或多匹配则抛出异常

例程：AnnotationIoC