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spring注解方式 2022/08/22

seven_ • • 后端漫谈 • 阅读 186

导读：本篇文章讲解 spring注解方式 2022/08/22，希望对大家有帮助，欢迎收藏，转发！站点地址：www.bmabk.com

spring注解方式

代码整体布局：

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代码如下：

pom.xml:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>org.example</groupId>
    <artifactId>mybatis_0822_KTLX</artifactId>
    <version>1.0-SNAPSHOT</version>

    <properties>
        <maven.compiler.source>8</maven.compiler.source>
        <maven.compiler.target>8</maven.compiler.target>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-context</artifactId>
            <version>5.3.18</version>
        </dependency>
    </dependencies>
</project>

spring-1.xml:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context https://www.springframework.org/schema/context/spring-context.xsd">

    <bean id="stu" class="com.test.Student" >
        <property name="name" value="张三"/>
        <property name="sex" value="男"/>
        <property name="age" value="20"/>
    </bean>
</beans>

Student:

package com.test;

import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;

//@Component:用于告诉spring，当前类的对象需要spring来管理。
//          里面的名字就相当于bean标签的id，作为对象的唯一标识
@Component("stu")
public class Student {
    private String name;
    private String sex;
    private Integer age;

    public Student() {
        System.out.println("=====Student 无参构造=====");
    }

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

    public String getName() {
        return name;
    }

    public void setName(String name) {
        System.out.println("========setName========:"+name);
        this.name = name;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    public Integer getAge() {
        return age;
    }

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

    @Override
    public String toString() {
        return "Student{" +
                "name='" + name + '\'' +
                ", sex='" + sex + '\'' +
                ", age=" + age +
                '}';
    }
}

Test:

package com.test;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

import javax.annotation.Resource;

public class Test {
    @Resource
    private Student stu;
    public static void main(String[] args) {
        //创建spring容器

        ApplicationContext ctx=new ClassPathXmlApplicationContext("spring-1.xml"); //运行结果：=====Student 无参构造===== ========setName========:张三
    }

}

Test2:

package com.test;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class Test2 {
    public static void main(String[] args) {
        //通过注解从spring容器中获取对象
        //1.在spring配置文件中，配置包扫描
        //2.在需要被spring管理的类上加特定注解
        ApplicationContext ctx=new ClassPathXmlApplicationContext("spring-1.xml");

        Student stu=ctx.getBean(Student.class);
        System.out.println(stu); //运行结果：=====Student 无参构造===== ========setName========:张三  Student{name='张三', sex='男', age=20}

        Student stu1=(Student)ctx.getBean("stu");
        System.out.println(stu1); //运行结果： Student{name='张三', sex='男', age=20}
    }
}

spring-2.xml:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context https://www.springframework.org/schema/context/spring-context.xsd">


    <context:component-scan base-package="com.test2"/>
</beans>

Car:

package com.test2;

import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;
import org.springframework.stereotype.Repository;
import org.springframework.stereotype.Service;

@Component("mycar") //通过注释，可以用在任意对象上
//@Service  //本质就是@Component这个注释的别名，用于Service层的对象
//@Repository //本质就是@Component这个注释的别名，用于数据访问层的对象
public class Car {
    //品牌
    @Value("宝马")
    private String brand;
    //价格
    @Value("2000")
    private int price;
    //时速
    @Value("120")
    private int space;

    public Car() {
    }

    public Car(String brand, int price, int space) {
        this.brand = brand;
        this.price = price;
        this.space = space;
    }

    public void run(){
        System.out.println(this.brand+"在跑");
    }

    public String getBrand() {
        return brand;
    }

    public void setBrand(String brand) {
        this.brand = brand;
    }

    public int getPrice() {
        return price;
    }

    public void setPrice(int price) {
        this.price = price;
    }

    public int getSpace() {
        return space;
    }

    public void setSpace(int space) {
        this.space = space;
    }

    @Override
    public String toString() {
        return "Car{" +
                "brand='" + brand + '\'' +
                ", price=" + price +
                ", space=" + space +
                '}';
    }
}

Driver:

package com.test2;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;

import javax.annotation.Resource;

@Component  //当注释没有指定id名字的时候，spring自动用类名小驼峰做对象的id名
public class Driver {
    //@Value只用于注入普通值
    @Value("张三")
    private String name;
    @Value("20")
    private Integer age;

    //@Autowired 用于注入对象类型的值（按照类型注入对象，前提是spring容器中有该类型的对象）
    //           该注释属于spring框架下的注释。特征是按照类型注入对象
    //@Autowired
    @Resource
    private Car car;

    public Driver() {
    }

    public Driver(String name, Integer age, Car car) {
        this.name = name;
        this.age = age;
        this.car = car;
    }

    //开车
    public void drive(){
        System.out.println(this.name+"开车");
        this.car.run();
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        //注解方式没有调用setter方法
        System.out.println("==========setName==============:"+name);
        this.name = name;
    }

    public Integer getAge() {
        return age;
    }

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

    public Car getCar() {
        return car;
    }

    public void setCar(Car car) {
        this.car = car;
    }

    @Override
    public String toString() {
        return "Driver{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", car=" + car +
                '}';
    }
}

Test:

package com.test2;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class Test {
    public static void main(String[] args) {
        ApplicationContext ctx=new ClassPathXmlApplicationContext("spring-2.xml");
        //获取容器中的司机对象
        Driver driver=ctx.getBean(Driver.class);
        //调用开车的方法
        driver.drive(); //运行结果：张三开车 宝马在跑


        Car car=ctx.getBean(Car.class);
        System.out.println(car);   //运行结果：Car{brand='宝马', price=2000, space=120}

        Car mycar=(Car)ctx.getBean("mycar");
        System.out.println(mycar); //运行结果：Car{brand='宝马', price=2000, space=120}
    }

}

spring-3.xml:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context https://www.springframework.org/schema/context/spring-context.xsd">

    <context:component-scan base-package="com.test3"/>
</beans>

IA:

package com.test3;

public interface IA {
    void test();
}

ClsA1:

package com.test3;

import org.springframework.stereotype.Component;

@Component
public class ClsA1 implements IA{
    @Override
    public void test() {
        System.out.println("这是A1测试");
    }
}

ClsA2:

package com.test3;

import org.springframework.stereotype.Component;

@Component
public class ClsA2 implements IA{
    @Override
    public void test() {
        System.out.println("这是A2测试");
    }
}

MyCls:

package com.test3;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.stereotype.Component;

import javax.annotation.Resource;

@Component //当注释没有指定id名字的时候，spring自动用类名小驼峰做对象的id名
public class MyCls {
//    @Autowired
//    private IA a;  //运行结果：ERROR:expected single matching bean but found 2: clsA1,clsA2

//    //@Autowired先按类型，再按照名字注入
//    @Autowired
//    private IA clsA1;    //指定名字注入。 ClsA1类名小写clsA1 。
//
//    public void show(){
//        this.clsA1.test();
//    }                   //运行结果：这是A1测试

    //@Autowired先按类型，再按照名字注入
    @Autowired
    @Qualifier("clsA1") //按名字注入对象a
    private IA a;

    public void show(){
        this.a.test();
    }                   //运行结果：这是A1测试

}

MyCls2:

package com.test3;

import org.springframework.stereotype.Component;

import javax.annotation.Resource;

@Component
public class MyCls2 {

//    @Resource(name = "clsA1")
//    private IA a;
//
//    public void show(){
//        this.a.test();
//    }                   //运行结果：这是A1测试

//    @Resource
//    private IA clsA1; //指定名字注入
//
//    public void show(){
//        this.clsA1.test();
//    }                   //运行结果：这是A1测试

//    //先按名字，再按类型注入
//    @Resource
//    private IA a;
//
//    public void show(){
//        this.a.test();
//    }  //运行结果：BeanNotOfRequiredTypeException: Bean named 'a' is expected to be of type 'com.test3.IA' but was actually of type 'com.test3.Dog'

    //先按名字，再按类型注入
    @Resource
    private IA a;

    public void show(){
        this.a.test();
    } //运行结果：NoUniqueBeanDefinitionException: No qualifying bean of type 'com.test3.IA' available: expected single matching bean but found 2: clsA1,clsA2
}

Dog:

package com.test3;

import org.springframework.stereotype.Component;

//@Component("a")
@Component("dog")
public class Dog {

}

Test:

package com.test3;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class Test {
    public static void main(String[] args) {
        ApplicationContext ac=new ClassPathXmlApplicationContext("spring-3.xml");
        MyCls myCls=ac.getBean(MyCls.class);
//        ac.getBean(MyCls.class);
        myCls.show();
    }
}

Test2:

package com.test3;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class Test2 {
    public static void main(String[] args) {
        ApplicationContext ac=new ClassPathXmlApplicationContext("spring-3.xml");
        MyCls2 myCls2=ac.getBean(MyCls2.class);
        myCls2.show();
    }

}

讲解参考：

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// A code block
var foo = 'bar';


// A code block
var foo = 'bar';


// A code block
var foo = 'bar';


// A code block
var foo = 'bar';


// A code block
var foo = 'bar';

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