13.Spring Bean标签说明及实例化方式

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Spring Bean标签说明及实例化方式

1.Bean标签

1.scope=”prototype”，默认值，Ioc容器只会创建一个该类型的对象

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package com.course.vo;

public class User {

	private Integer id;
	private String name;
	private String address;
	
	public Integer getId() {
		return id;
	}
	public void setId(Integer id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public String getAddress() {
		return address;
	}
	public void setAddress(String address) {
		this.address = address;
	}	
}
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<?xml version="1.0" encoding="UTF-8"?>
<!-- 头文件 -->
<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="user1" class="com.course.vo.User"></bean>
	<bean id="user3" class="com.course.vo.User"></bean>
	
</beans>
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package com.test;

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

import com.course.vo.User;

public class TestMain {

	public static void main(String[] args) {
		ApplicationContext applicationContext = new ClassPathXmlApplicationContext("classpath:applicationContext.xml");
		
	        User user1 = (User) applicationContext.getBean("user1");
			User user2 = (User) applicationContext.getBean("user1");
		
			System.out.println(user1);
			System.out.println(user2);
			System.out.println(user1 == user2);
			// com.course.vo.User@2a266d09
            // com.course.vo.User@2a266d09
            // true

			User user3 = (User) applicationContext.getBean("user3");
			System.out.println(user3);
			System.out.println(user1 == user3);
            // com.course.vo.User@5ab9e72c
			// false
		
	}
}

2.scope=”prototype”，每次调用IoC容器都会新创建一个该类型的对象，

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<?xml version="1.0" encoding="UTF-8"?>
<!-- 头文件 -->
<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="user1" class="com.course.vo.User" scope="prototype"></bean>
	
</beans>
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package com.test;

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

import com.course.vo.User;

public class TestMain {

	public static void main(String[] args) {
		ApplicationContext applicationContext = new ClassPathXmlApplicationContext("classpath:applicationContext.xml");
		
		User user1 = (User) applicationContext.getBean("user1");
		User user2 = (User) applicationContext.getBean("user1");
		
		System.out.println(user1);
		System.out.println(user2);		
		System.out.println(user1 == user2);
		// com.course.vo.User@2a266d09
		// com.course.vo.User@5ab9e72c
		// false
		
	}
}

3.scope=”singleton”，只要Spring启动加载了applicationContext.xml文件，就会创建对象

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package com.course.vo;

public class User {

	private Integer id;
	private String name;
	private String address;
	
	public User() {
		super();
		System.out.println("创建User对象");
	}
	public Integer getId() {
		return id;
	}
	public void setId(Integer id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public String getAddress() {
		return address;
	}
	public void setAddress(String address) {
		this.address = address;
	}
}
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<?xml version="1.0" encoding="UTF-8"?>
<!-- 头文件 -->
<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="user1" class="com.course.vo.User"></bean>
</beans>
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package com.test;

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

import com.course.vo.User;

public class TestMain {

	public static void main(String[] args) {
		ApplicationContext applicationContext = new ClassPathXmlApplicationContext("classpath:applicationContext.xml");
		// 创建User对象
	}
}

4.scope=”prototype”，只有在从获取IoC容器中获取对象的时候，才会创建对象，获取几次对象，就创建几次对象，不去获取对象，就不创建对象。

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<?xml version="1.0" encoding="UTF-8"?>
<!-- 头文件 -->
<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="user1" class="com.course.vo.User" scope="prototype"></bean>
</beans>
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package com.test;

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

import com.course.vo.User;

public class TestMain {

	public static void main(String[] args) {
		// (控制台没有输出)
	}
}
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package com.test;

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

import com.course.vo.User;

public class TestMain {

	public static void main(String[] args) {
		ApplicationContext applicationContext = new ClassPathXmlApplicationContext("classpath:applicationContext.xml");
		
		User user1 = (User) applicationContext.getBean("user1");
		User user2 = (User) applicationContext.getBean("user1");
		// 创建User对象
		// 创建User对象
	}
}

5.<bean>标签的属性配置

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<?xml version="1.0" encoding="UTF-8"?>
<!-- 头文件 -->
<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">
  	<!-- 
  		id: 对象在IoC容器里的key，唯一标识
  		class: 类的完全限定名
  		scope:
  			- singleton(default): Ioc容器只会创建一个该类型的对象，
  			- prototype: 每次调用IoC容器都会新创建一个该类型的对象，
  			- request: 在web项目，每个request只会创建一个对象
  			- session: 在web项目，每个session只会创建一个对象
  		name: 在SpringMVC中指定Controller的请求路径
  		lazy-init: 是否懒加载
  			- default: 默认值为false，IoC容器启动时就会创建该对象
  			- true: 只有调用该对象，才会创建
  			- false: IoC容器启动时就会创建该对象
  	 -->
	<bean id="user1" class="com.course.vo.User" scope="singleton" lazy-init="true"></bean>
</beans>

6.scope属性与lazy-init属性
|scope|lazy-init|结果|
|-|-|-|
|singleton|true|调用对象时才创建对象，不调用对象就不创建，多次调用同一个bean，只会创建一个|
|singleton|false|在IoC容器启动时就会创建对象，只会创建一个|
|prototype|true/false|均为懒加载，调用时才创建对象，不调用不创建对象，每次调用都创建一个新的对象|

7.创建一个Date对象

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<?xml version="1.0" encoding="UTF-8"?>
<!-- 头文件 -->
<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="date1" class="java.util.Date"></bean>
</beans>
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package com.test;

import java.util.Date;

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

public class TestMain {

	public static void main(String[] args) {
		ApplicationContext applicationContext = new ClassPathXmlApplicationContext("classpath:applicationContext.xml");
		Date date1 = (Date) applicationContext.getBean("date1");
		System.out.println(date1);
		// Wed Dec 01 17:10:51 CST 2021
	}
}

2.Spring实例化Bean的3种方式

1.使用类的无参的构造方式

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<?xml version="1.0" encoding="UTF-8"?>
<!-- 头文件 -->
<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="user2" class="com.course.vo.User"></bean>	
</beans>
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package com.test;

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

import com.course.vo.User;

public class TestMain {

	public static void main(String[] args) {
		ApplicationContext applicationContext = new ClassPathXmlApplicationContext("classpath:applicationContext.xml");
		User user2 = (User) applicationContext.getBean("user2");
		System.out.println(user2);
		// 创建User对象
		// com.course.vo.User@2a266d09
	}
}

2.使用静态工厂

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package com.course.factory;

import com.course.vo.User;

public class UserFactory {

	public static User getUser1() {
		User user = new User();
		user.setId(1);
		user.setName("name1");
		user.setAddress("address1");
		return user;
	}
	
	public static User getUser2() {
		User user = new User();
		user.setId(2);
		user.setName("name2");
		user.setAddress("address2");
		return user;
	}
	
}
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<?xml version="1.0" encoding="UTF-8"?>
<!-- 头文件 -->
<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">
    
	<!-- 
		使用静态工厂
		class: 静态工厂类的全限定名
		factory-method: 静态工厂类的方法
	 -->
	<bean id="user1" class="com.course.factory.UserFactory" factory-method="getUser1"></bean>
	<bean id="user2" class="com.course.factory.UserFactory" factory-method="getUser2"></bean>
</beans>
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package com.test;

import java.util.Date;

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

import com.course.vo.User;

public class TestMain {

	public static void main(String[] args) {
		ApplicationContext applicationContext = new ClassPathXmlApplicationContext("classpath:applicationContext.xml");
		
		User user1 = (User) applicationContext.getBean("user1");
		User user2 = (User) applicationContext.getBean("user2");
		
		// User类添加了toString()方法
		System.out.println(user1);
		System.out.println(user2);
		// User [id=1, name=name1, address=address1]
		// User [id=2, name=name2, address=address2]
		
	}
}

3.使用实例工厂

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package com.course.factory;

import com.course.vo.User;

public class UserFactory {

	public User getUser3() {
		User user = new User();
		user.setId(3);
		user.setName("name3");
		user.setAddress("address3");
		return user;
	}
	
}
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<?xml version="1.0" encoding="UTF-8"?>
<!-- 头文件 -->
<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">
        
	<!-- 使用实例工厂 -->
	<!-- 声明实例工厂 -->
	<bean id="userFactory" class="com.course.factory.UserFactory"></bean>
	<!-- 
		factory-bean: 实例工厂的bean的id
		factory-method: 实例工厂的方法名
	 -->
	<bean id="user3" factory-bean="userFactory" factory-method="getUser3"></bean>	
</beans>
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package com.test;

import java.util.Date;

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

import com.course.vo.User;

public class TestMain {

	public static void main(String[] args) {
		ApplicationContext applicationContext = new ClassPathXmlApplicationContext("classpath:applicationContext.xml");
		User user3 = (User) applicationContext.getBean("user3");
		System.out.println(user3);
	}
}

3.Bean属性的注入

1.使用set()方法注入

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package com.course.vo;

import java.util.Date;

public class User {

	private Integer id;
	private String name;
	private String address;
	private Date hireDate;
	
	public User() {
		super();
		
	}
	public Integer getId() {
		return id;
	}
	public void setId(Integer id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public String getAddress() {
		return address;
	}
	public void setAddress(String address) {
		this.address = address;
	}
	public Date getHireDate() {
		return hireDate;
	}
	public void setHireDate(Date hireDate) {
		this.hireDate = hireDate;
	}
	@Override
	public String toString() {
		return "User [id=" + id + ", name=" + name + ", address=" + address + ", hireDate=" + hireDate + "]";
	}
}
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<?xml version="1.0" encoding="UTF-8"?>
<!-- 头文件 -->
<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="date1" class="java.util.Date"></bean>
	
	<bean id="user1" class="com.course.vo.User">
		<property name="id" value="1"></property>
		<property name="name" value="name1"></property>
		<property name="address" value="address1"></property>
		<property name="hireDate" ref="date1"></property>
	</bean>
		
</beans>
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package com.test;

import java.util.Date;

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

import com.course.vo.User;

public class TestMain {

	public static void main(String[] args) {
		ApplicationContext applicationContext = new ClassPathXmlApplicationContext("classpath:applicationContext.xml");
		User user1 = (User) applicationContext.getBean("user1");
		System.out.println(user1);
		// User [id=1, name=name1, address=address1, hireDate=Wed Dec 01 17:56:49 CST 2021]
	}
}

2.使用有参的构造方法注入

(1)使用<constructor-arg index="2">，index指定构造方法的参数的索引位置，会根据构造方法的形参去选择相应的构造方法

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package com.course.vo;

import java.util.Date;

public class User {

	private Integer id;
	private String name;
	private String address;
	private Date hireDate;
	
	public User() {
		super();
		
	}
	
	public User(Integer id, String address, String name) {
		super();
		this.id = id;
		this.name = name;
		this.address = address;
	}

	public User(Integer id, String name) {
		super();
		this.id = id;
		this.name = name;
	}
	
	public User(Integer id, String name, String address, Date hireDate) {
		super();
		this.id = id;
		this.name = name;
		this.address = address;
		this.hireDate = hireDate;
	}

	public Integer getId() {
		return id;
	}
	public void setId(Integer id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public String getAddress() {
		return address;
	}
	public void setAddress(String address) {
		this.address = address;
	}
	public Date getHireDate() {
		return hireDate;
	}
	public void setHireDate(Date hireDate) {
		this.hireDate = hireDate;
	}
	@Override
	public String toString() {
		return "User [id=" + id + ", name=" + name + ", address=" + address + ", hireDate=" + hireDate + "]";
	}
}
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<?xml version="1.0" encoding="UTF-8"?>
<!-- 头文件 -->
<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="user1" class="com.course.vo.User">
		<constructor-arg index="0" value="1"></constructor-arg>
		<constructor-arg index="1" value="param1"></constructor-arg>
		
	</bean>
</beans>
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package com.test;

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

import com.course.vo.User;

public class TestMain {

	public static void main(String[] args) {
		ApplicationContext applicationContext = new ClassPathXmlApplicationContext("classpath:applicationContext.xml");
		User user1 = (User) applicationContext.getBean("user1");
		System.out.println(user1);
		// User [id=1, name=param1, address=null, hireDate=null]
	}
}
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<?xml version="1.0" encoding="UTF-8"?>
<!-- 头文件 -->
<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="user1" class="com.course.vo.User">
		<constructor-arg index="0" value="1"></constructor-arg>
		<constructor-arg index="1" value="param1"></constructor-arg>
		<constructor-arg index="2" value="param2"></constructor-arg>
	</bean>
</beans>
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package com.test;

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

import com.course.vo.User;

public class TestMain {

	public static void main(String[] args) {
		ApplicationContext applicationContext = new ClassPathXmlApplicationContext("classpath:applicationContext.xml");
		User user1 = (User) applicationContext.getBean("user1");
		System.out.println(user1);
		// User [id=1, name=param2, address=param1, hireDate=null]
	}
}

(2)使用<constructor-arg name=""，name指定构造方法的参数名

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<?xml version="1.0" encoding="UTF-8"?>
<!-- 头文件 -->
<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="user1" class="com.course.vo.User">
		<constructor-arg name="id" value="1"></constructor-arg>
		<constructor-arg name="name" value="param1"></constructor-arg>
		<constructor-arg name="address" value="param2"></constructor-arg>
	</bean>
</beans>
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package com.test;

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

import com.course.vo.User;

public class TestMain {

	public static void main(String[] args) {
		ApplicationContext applicationContext = new ClassPathXmlApplicationContext("classpath:applicationContext.xml");
		User user1 = (User) applicationContext.getBean("user1");
		System.out.println(user1);
		// User [id=1, name=param1, address=param2, hireDate=null]
	}
}

(3) 其他属性ref和type

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<?xml version="1.0" encoding="UTF-8"?>
<!-- 头文件 -->
<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="date1" class="java.util.Date"></bean>
	<!-- 

		- ref: 注入的IoC容器里的对象
		- type: 参数类型
	 -->
	<bean id="user1" class="com.course.vo.User">
		<constructor-arg name="id" value="1" type="java.lang.Integer"></constructor-arg>
		<constructor-arg name="name" value="param1" type="java.lang.String"></constructor-arg>
		<constructor-arg name="address" value="param2" type="java.lang.String"></constructor-arg>
		<constructor-arg name="hireDate" ref="date1" type="java.util.Date"></constructor-arg>
	</bean>
</beans>
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package com.test;

import java.util.Date;

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

import com.course.vo.User;

public class TestMain {

	public static void main(String[] args) {
		ApplicationContext applicationContext = new ClassPathXmlApplicationContext("classpath:applicationContext.xml");
		User user1 = (User) applicationContext.getBean("user1");
		System.out.println(user1);
		// User [id=1, name=param1, address=param2, hireDate=Wed Dec 01 18:25:11 CST 2021]
	}
}