Define Student and Teacher classes for testing

  • Student
public class Student {
    private String name;
    private Integer age;

    public Student(a) {}public Student(Integer age, String name) {
        this.age = age;
        this.name = name;
    }

    public Integer getAge(a) {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public String getName(a) {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public void printStu(a) {
        System.out.println("this is Student's method!"); }}Copy the code
  • Teacher
public class Teacher {

    private Student student;

    public void print(a) {
        System.out.println(student.getName() + ""+ student.getAge()); student.printStu(); }}Copy the code



First, the @autowired

  • The XML configuration file is:
    <bean id="teacher" class="spring5.Annotation.Teacher">

    </bean>

    <bean id="student" class="spring5.Annotation.Student">
        <property name="name" value="nash"></property>
        <property name="age" value="18"></property>
    </bean>
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1.1@Autowired’s automatic assembly method

  • AutowiredAccording to thebyTypeThe way to match inThe Ioc containerLook forBeanWhen there is only one Bean, Spring does property injection; otherwise, it throws an exception
  • Autowired is not assembled through the set function, so the Teacher classYou don't need setter methods
    @Autowired
    private Student student;
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  • Autowired annotations can be used not only on fields, but also onConstructor, setter method

As used on a constructor:

@Autowired
public Teacher(Student student) {
        this.student = student;
}
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1.2 Running Results




Second, @ Qulifier

2.1 Usage of @qulifier

  • @QulifierCooperate with@AutowiredUsed when there are multiple beans of the same type

For example, two studentBeans are configured in the XML file:

    <bean id="student1" class="spring5.Annotation.Student">
        <property name="name" value="nash"></property>
        <property name="age" value="18"></property>
    </bean>

    <bean id="student2" class="spring5.Annotation.Student">
        <property name="name" value="dana"></property>
        <property name="age" value="19"></property>
    </bean>
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In this case, @autoWired should be used in conjunction with @Qulifier

@Autowired
@Qualifier("student2")
private Student student;
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2.2 Running Results




Third, @ the Resource

3.1 Automatic assembly of @Resource

  • if@ResourceIf nothing follows, Spring presses by defaultbyNameTo match. In terms ofbyNameIf there are multiple beans of the same type, an exception will be thrown
    <bean id="student" class="spring5.Annotation.Student">
        <property name="name" value="nash"></property>
        <property name="age" value="18"></property>
    </bean>
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@Resource
private Student student;
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Running results:

  • If I specify at sign ResourcenameortypeIs matched according to the specified name or type
<bean id="stu" class="spring5.Annotation.Student">
     <property name="name" value="nash"></property>
     <property name="age" value="18"></property>
</bean>
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@Resource(name = "stu")
private Student student;
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Running results:

If type is specified, something like this:

@Resource(type = Student.class)
private Student student;
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3.2 The difference between @autowired and @Resource

  • @AutowiredThe default in accordance with thebyTypeAnd the@ResourceThe default in accordance with thebyNamematching
  • @Autowired 是Spring“, while@Resource 是J2EEthe



Fourth, @ the Value

  • @value is not commonly used and is generally used to inject common types (e.gString, intEtc.)
  • There are three ways to fill in @Value

4.1@value (” “)

  • Inject plain types directly
@Value("nash")
private String name;

@Value("1")
private int age;

@Value("https://www.csdn.net")
private Resource path;
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4.2 @value (#{})

  • saidSpEl expressionIt is usually used to get a bean property, or to call a bean method, or to represent a constant
  • When a bean obtains a property of another bean via @value (” #{} “) or calls a method of another bean, as long as the bean(Beab_A) has access to the bean being called (Beab_B), that is, Beab_A and Beab_B are either in the same container, Or the container where Beab_B resides is the parent of the container where Beab_A resides.
@Value("#{T(java.lang.Math).random() * 100}")
private Integer age;
 
@Value("#{systemProperties['os.name']}")
private String osName;
 
@Value("#{1}")
private int number; // Get the number 1
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See SpEl expressions for details

4.3 @value (${})

  • It is used to obtain the attribute value of an external configuration file

Such as config. The properties

name = nash
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@Value("${name}")
private String name;
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reference

Spring @value annotation assignment