Dependency injection in spring

IOC role: reduce the coupling between programs (dependency)
Dependency management: to be maintained by spring (objects of other classes are needed in the current class, provided by spring, we only need to explain in the configuration file)
Dependency maintenance: dependency injection
Dependency injection:
Data that can be injected:

1. Basic types and strings
2. Other bean types (beans configured in configuration files or annotations)
3. Complex type / set type

How to inject bean objects:

1. Using constructors
2. Using the set function
3. Use annotations

Using constructors

Constructor entry:|
Label used: constructor- arg
Where the tag appears: inside the bean tag
Properties in Tags
Type: Specifies the data type of the data to be injected, which is also the type of one or some parameters in the constructor
Index: used to specify the data to be injected to assign a value to the parameter in the constructor that specifies the index position. Index position starts from e
Name: commonly used for parameter assignment to the specified name in the constructor
=========The three above are used to specify which parameter assignment in the constructor
value: used to provide data of basic type and String type
ref: used to specify other bean type data. It refers to the core containers of Ioc in spring

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
    <bean id="accountService" class="com.ay.service.impl.AccountServiceImpl">
        <constructor-arg name="name" value="Flying"></constructor-arg>
        <constructor-arg name="age" value="20"></constructor-arg>
        <constructor-arg name="birthday" ref="now"></constructor-arg>
    </bean>
    <bean id="now" class="java.util.Date" ></bean>
</beans>

package com.ay.service;

public interface AccountService {
    public  void saveAccount();
}

package com.ay.service.impl;

 import com.ay.service.AccountService;

 import java.util.Date;

public class AccountServiceImpl implements AccountService {
    private String name;
    private Integer age;
    private Date birthday;
    @Override
    public void saveAccount() {
        System.out.println("Method created successfully");
    }

    public AccountServiceImpl(String name, Integer age, Date birthday) {
        this.name = name;
        this.age = age;
        this.birthday = birthday;
    }

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

package com.ay.ui;

import com.ay.service.AccountService;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class Client {
    public static void main(String[] args) {
        ApplicationContext ac = new ClassPathXmlApplicationContext("bean.xml");
        AccountService as = (AccountService)ac.getBean("accountService");
        as.saveAccount();
        System.out.println(as.toString());
    }
}

Conclusion:
Advantage: when getting the bean object, injecting data is a necessary operation, otherwise the object cannot be created successfully.
Disadvantage: it changes the instantiation method of bean objects, so that when we create objects, if we can't use these data, we must also provide them.

Using the set function

Tags involved: property
Where it appears: inside the bean tag
Properties of the label
Name: used to specify the set method name called in
value: used to provide data of basic type and String type
ref: used to specify other bean type data. It refers to the bean objects that have appeared in the Ioc core container of spring

package com.ay.service;

public interface AccountService {
    public  void saveAccount();
}

package com.ay.service.impl;

 import com.ay.service.AccountService;

 import java.util.Date;

public class AccountServiceImpl implements AccountService {
    private String name;
    private Integer age;
    private Date birthday;
    @Override
    public void saveAccount() {
        System.out.println("Method created successfully");
    }

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

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

    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }

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

package com.ay.ui;

import com.ay.service.AccountService;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class Client {
    public static void main(String[] args) {
        ApplicationContext ac = new ClassPathXmlApplicationContext("bean.xml");
        AccountService as = (AccountService)ac.getBean("accountService");
        as.saveAccount();
        System.out.println(as.toString());
    }
}

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
    <bean id="accountService" class="com.ay.service.impl.AccountServiceImpl">
        <property name="name" value="Flying"></property>
        <property name="age" value="20"></property>
        <property name="birthday" ref="now"></property>
     </bean>
    <bean id="now" class="java.util.Date" ></bean>
</beans>

Conclusion:
Advantage: there is no explicit restriction when creating objects, and you can directly use the default constructor
Disadvantage: if a member must have a value, it is possible that the set method is not executed.