The difference between @Autowired and @Resource
Test preparation
Create Student, School, and PrimarySchool classes and use annotations to assign basic data types
//Student引用school
public class Student {
private School school;
@Value("张三")
private String sname;
@Value("22")
private int sage;
public School getSchool() {
return school;
}
public void setSchool(School school) {
this.school = school;
}
public String getSname() {
return sname;
}
public void setSname(String sname) {
this.sname = sname;
}
public int getSage() {
return sage;
}
public void setSage(int sage) {
this.sage = sage;
}
@Override
public String toString() {
return "Student{" +
"school=" + school +
", sname='" + sname + '\'' +
", sage=" + sage +
'}';
}
}
public class School {
@Value("北京大学附属一中")
private String name;
@Value("私立小学")
private String type;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getType() {
return type;
}
public void setType(String type) {
this.type = type;
}
@Override
public String toString() {
return "School{" +
"name='" + name + '\'' +
", type='" + type + '\'' +
'}';
}
}
//PrimarySchool是School 的子类
public class PrimarySchool extends School {
}
Scan package configuration in spring configuration file
<!-- 扫描注解，这样com.liu包下的文件都能被扫描 -->
<context:component-scan base-package="com.liu.pojo"/>
Test class
public class StudentTest {
@Test
public void test(){
ClassPathXmlApplicationContext classPathXmlApplicationContext = new ClassPathXmlApplicationContext("applicationContext.xml");
Student myStudent =(Student) classPathXmlApplicationContext.getBean("student");
System.out.println(myStudent);
}
}
Test one (@Autowired default type)
The annotation method introduces Student into spring
and adds @Autowired annotation to the school attribute of Student. The
annotation method introduces PrimarySchool into spring
@Component
public class Student {
@Autowired
private School school;
@Value("张三")
private String sname;
@Value("22")
private int sage;
//。。。省略其他代码
}
@Component("myShool")
public class PrimarySchool extends School {
}
After the test class runs, the result 1 is
then delete the @Component annotation of PrimarySchool, and add the @Component annotation to the School class
public class PrimarySchool extends School {
}
@Component("myShool")
public class School {
@Value("北京大学附属一中")
private String name;
@Value("私立小学")
private String type;
//。。。省略其他代码
}
Result after the test class is run 2
Test one conclusion
According to the results 1 and 2 after running, it can be seen that the school attribute of Student can be added @Autowired to introduce the School type or the subclass PrimarySchool of School, and the specified value of @Component("myShool") is not "shool", thus It is concluded that **@Autowired belongs to the bytype type by default, @Autowired can automatically introduce objects of the same type by default (that is, objects of a certain type or subclass objects of this type can be introduced), and the id of the been in spring (that is, "MyShool") specified by @Component("myShool") does not matter **
Test two (@Autowired type can also set the byName introduction method)
@Qualifier("school") can introduce @Autowired into the way set byName
@Autowired(required = false)required The default is true. If school is null, cuo will be reported, and required = false will not report an error
@Component
public class Student {
@Autowired(required = false)
@Qualifier("school")
private School school;
@Value("张三")
private String sname;
@Value("22")
private int sage;
//。。。省略其他代码
}
After the test class is run, the result 3
sets the value specified by Qualifier to the id of the spring specified object (that is, the value specified by the myShool class @Component("myShool"))
@Component
public class Student {
@Autowired(required = false)
@Qualifier("myShool")
private School school;
@Value("张三")
private String sname;
@Value("22")
private int sage;
//。。。省略其他代码
}
Result after running the test class 4
Test two conclusion
@Qualifier annotation can set @Autowired introduction method to byName
Test three (@Resource is first introduced according to byName, if byName is not found, it will be imported according to byType)
PrimarySchool class @Component specified value is "myShool"
School of Student class is introduced by @Resource
@Component("myShool")
public class PrimarySchool extends School {
}
public class School {
@Value("北京大学附属一中")
private String name;
@Value("私立小学")
private String type;
//。。。省略其他代码
}
@Component
public class Student {
@Resource
private School school;
@Value("张三")
private String sname;
@Value("22")
private int sage;
//。。。省略其他代码
}
The result after the test class is run 5
Set the @Resource of Student to only use the byName method @Resource(name = "school")
@Component
public class Student {
@Resource(name = "school")
private School school;
@Value("张三")
private String sname;
@Value("22")
private int sage;
//。。。省略其他代码
}
The result after the test class is run 7
Test three conclusion
@Resource is first introduced according to byName by default. If byName is not found, it will be imported according to byType. If @Resource sets the byName method, if the id of been cannot be found, an error will be reported.