优质全套Spring全套教程一

<dependencies>
     <!-- 基于Maven依赖传递性，导入spring-context依赖即可导入当前所需所有jar包 -->
     <dependency>
         <groupId>org.springframework</groupId>
         <artifactId>spring-context</artifactId>
         <version>5.3.1</version>
     </dependency>
     <!-- junit测试 -->
     <dependency>
         <groupId>junit</groupId>
         <artifactId>junit</artifactId>
         <version>4.12</version>
         <scope>test</scope>
     </dependency>
 </dependencies>

public class HelloWorld {
     public void sayHello(){
         System.out.println("helloworld");
     }
 }

 <!--
     配置HelloWorld所对应的bean，即将HelloWorld的对象交给Spring的IOC容器管理
     通过bean标签配置IOC容器所管理的bean
     属性：
         id：设置bean的唯一标识
         class：设置bean所对应类型的全类名
 -->
 <bean id="helloworld" class="com.atguigu.spring.bean.HelloWorld"></bean>

 @Test
 public void testHelloWorld(){
     ApplicationContext ioc = new ClassPathXmlApplicationContext("applicationContext.xml");
     HelloWorld helloworld = (HelloWorld) ioc.getBean("helloworld");
     helloworld.sayHello();
 }

org.springframework.beans.factory.BeanCreationException: Error creating bean with name

'helloworld' defined in class path resource [applicationContext.xml]: Instantiation of bean

failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed

to instantiate [com.atguigu.spring.bean.HelloWorld]: No default constructor found; nested

exception is java.lang.NoSuchMethodException: com.atguigu.spring.bean.HelloWorld.

<init>()

@Test
 public void testHelloWorld(){
     ApplicationContext ac = new ClassPathXmlApplicationContext("applicationContext.xml");
     HelloWorld bean = ac.getBean(HelloWorld.class);
     bean.sayHello();
 }

@Test
 public void testHelloWorld(){
     ApplicationContext ac = new ClassPathXmlApplicationContext("applicationContext.xml");
     HelloWorld bean = ac.getBean("helloworldOne", HelloWorld.class);
     bean.sayHello();
 }

<bean id="helloworldOne" class="com.atguigu.spring.bean.HelloWorld"></bean>
 <bean id="helloworldTwo" class="com.atguigu.spring.bean.HelloWorld"></bean>

org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean

of type 'com.atguigu.spring.bean.HelloWorld' available: expected single matching bean but

found 2: helloworldOne,helloworldTwo

public class Student {
    private Integer id;
    private String name;
    private Integer age;
    private String sex;
    public Student() {
    }
    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 Integer getAge() {
        return age;
    }
    public void setAge(Integer age) {
        this.age = age;
    }
    public String getSex() {
        return sex;
    }
    public void setSex(String sex) {
        this.sex = sex;
    }
    @Override
    public String toString() {
        return "Student{" +
            "id=" + id +
            ", name='" + name + '\'' +
            ", age=" + age +
            ", sex='" + sex + '\'' +
            '}';
    }
}

<bean id="studentTwo" class="com.atguigu.spring.pojo.Student">
    <!-- property标签：通过组件类的setXxx()方法给组件对象设置属性 -->
    <!-- name属性：指定属性名（这个属性名是getXxx()、setXxx()方法定义的，和成员变量无关）-->
    <!-- value属性：指定属性值 -->
    <property name="id" value="1001"></property>
    <property name="name" value="张三"></property>
    <property name="age" value="23"></property>
    <property name="sex" value="男"></property>
</bean>

public void testDIBySet(){
    ApplicationContext ac = new ClassPathXmlApplicationContext("spring-ioc.xml");
    Student studentTwo = ac.getBean("studentTwo", Student.class);//这里测试用id和类型，用的多的还是根据类型获取
    System.out.println(studentTwo);
}

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

<bean id="studentTwo" class="com.atguigu.spring.bean.Student">
    <constructor-arg value="1002"></constructor-arg>
    <constructor-arg value="李四"></constructor-arg>
    <constructor-arg value="33"></constructor-arg>
    <constructor-arg value="女"></constructor-arg>
</bean>

@Test
public void testDIBySet(){
    ApplicationContext ac = new ClassPathXmlApplicationContext("springdi.xml");
    Student studentOne = ac.getBean("studentTwo", Student.class);
    System.out.println(studentOne);
}

<property name="name">
  <null />
</property>

<property name="name" value="null"></property>

<!-- 小于号在XML文档中用来定义标签的开始，不能随便使用 -->
<!-- 解决方案一：使用XML实体来代替 -->
<property name="expression" value="a &lt; b"/>

<property name="expression">
    <!-- 解决方案二：使用CDATA节 -->
    <!-- CDATA中的C代表Character，是文本、字符的含义，CDATA就表示纯文本数据 -->
    <!-- XML解析器看到CDATA节就知道这里是纯文本，就不会当作XML标签或属性来解析 -->
    <!-- 所以CDATA节中写什么符号都随意 -->
    <value><![CDATA[a < b]]></value>
</property>

public class Clazz {
    private Integer clazzId;
    private String clazzName;
    public Integer getClazzId() {
        return clazzId;
    }
    public void setClazzId(Integer clazzId) {
        this.clazzId = clazzId;
    }
    public String getClazzName() {
        return clazzName;
    }
    public void setClazzName(String clazzName) {
        this.clazzName = clazzName;
    }
    @Override
    public String toString() {
        return "Clazz{" +
            "clazzId=" + clazzId +
            ", clazzName='" + clazzName + '\'' +
            '}';
    }
    public Clazz() {
    }
    public Clazz(Integer clazzId, String clazzName) {
        this.clazzId = clazzId;
        this.clazzName = clazzName;
    }
}

private Clazz clazz;
public Clazz getClazz() {
    return clazz;
}
public void setClazz(Clazz clazz) {
    this.clazz = clazz;
}

<bean id="clazzOne" class="com.atguigu.spring.pojo.Clazz">
    <property name="clazz.cid" value="1111"></property>
    <property name="clazz.cname" value="财源滚滚班"></property>
</bean>

<bean id="studentFour" class="com.atguigu.spring.pojo.Student">
    <property name="id" value="1004"></property>
    <property name="name" value="赵六"></property>
    <property name="age" value="26"></property>
    <property name="sex" value="女"></property>
    <!-- ref属性：引用IOC容器中某个bean的id，将所对应的bean为属性赋值 -->
    <property name="clazz" ref="clazzOne"></property>
</bean>

<bean id="studentFour" class="com.atguigu.spring.pojo.Student">
    <property name="id" value="1004"></property>
    <property name="name" value="赵六"></property>
    <property name="age" value="26"></property>
    <property name="sex" value="女"></property>
    <property name="clazz" value="clazzOne"></property>
</bean>

<bean id="studentFour" class="com.atguigu.spring.pojo.Student">
    <property name="id" value="1004"></property>
    <property name="name" value="赵六"></property>
    <property name="age" value="26"></property>
    <property name="sex" value="女"></property>
    <property name="clazz">
        <!-- 在一个bean中再声明一个bean就是内部bean -->
        <!-- 内部bean只能用于给属性赋值，不能在外部通过创建IOC容器获取，因此可以省略id属性 -->
        <bean id="clazzInner" class="com.atguigu.spring.pojo.Clazz">
            <property name="cid" value="2222"></property>
            <property name="cname" value="远大前程班"></property>
        </bean>
    </property>
</bean>

<bean id="studentFour" class="com.atguigu.spring.pojo.Student">
    <property name="id" value="1004"></property>
    <property name="name" value="赵六"></property>
    <property name="age" value="26"></property>
    <property name="sex" value="女"></property>
    <!-- 一定先引用某个bean为属性赋值或者实例化，才可以使用级联方式更新属性 -->
    <property name="clazz" ref="clazzOne"></property>
    <property name="clazz.cid" value="3333"></property>
    <property name="clazz.cname" value="最强王者班"></property>
</bean>

private String[] hobbies;
public String[] getHobbies() {
    return hobbies;
}
public void setHobbies(String[] hobbies) {
    this.hobbies = hobbies;
}

<bean id="studentFour" class="com.atguigu.spring.bean.Student">
    <property name="id" value="1004"></property>
    <property name="name" value="赵六"></property>
    <property name="age" value="26"></property>
    <property name="sex" value="女"></property>
    <!-- ref属性：引用IOC容器中某个bean的id，将所对应的bean为属性赋值 -->
    <property name="clazz" ref="clazzOne"></property>
    <property name="hobbies">
        <array>
            <value>抽烟</value>
            <value>喝酒</value>
            <value>烫头</value>
        </array>
    </property>
</bean>

private List<Student> students;
public List<Student> getStudents() {
    return students;
}
public void setStudents(List<Student> students) {
    this.students = students;
}
配置bean：

<bean id="clazzTwo" class="com.atguigu.spring.bean.Clazz">
    <property name="cid" value="4444"></property>
    <property name="cname" value="Javaee0222"></property>
    <property name="students">
        <list>
            <ref bean="studentOne"></ref>
            <ref bean="studentTwo"></ref>
            <ref bean="studentThree"></ref>
        </list>
    </property>
</bean>

<bean id="clazzTwo" class="com.atguigu.spring.bean.Clazz">
    <property name="cid" value="4444"></property>
    <property name="cname" value="Javaee0222"></property>
    <property name="students">
        <list>
            <ref bean="studentOne"></ref>
            <ref bean="studentTwo"></ref>
            <ref bean="studentThree"></ref>
        </list>
    </property>
</bean>

public class Teacher {
    private Integer teacherId;
    private String teacherName;
    public Integer getTeacherId() {
        return teacherId;
    }
    public void setTeacherId(Integer teacherId) {
        this.teacherId = teacherId;
    }
    public String getTeacherName() {
        return teacherName;
    }
    public void setTeacherName(String teacherName) {
        this.teacherName = teacherName;
    }
    public Teacher(Integer teacherId, String teacherName) {
        this.teacherId = teacherId;
        this.teacherName = teacherName;
    }
    public Teacher() {
    }
    @Override
    public String toString() {
        return "Teacher{" +
            "teacherId=" + teacherId +
            ", teacherName='" + teacherName + '\'' +
            '}';
    }
}

private Map<String, Teacher> teacherMap;
public Map<String, Teacher> getTeacherMap() {
    return teacherMap;
}
public void setTeacherMap(Map<String, Teacher> teacherMap) {
    this.teacherMap = teacherMap;
}

spring-ioc.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:util="http://www.springframework.org/schema/util"
       xmlns:p="http://www.springframework.org/schema/p"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/util https://www.springframework.org/schema/util/spring-util.xsd">

    <bean id="studentOne" class="com.atguigu.spring.pojo.Student"></bean>

    <bean id="studentTwo" class="com.atguigu.spring.pojo.Student">
        <!--
            property：通过成员变量的set方法进行赋值
            name：设置需要赋值的属性名（和set方法有关）
            value：设置为属性所赋的值
        -->
        <property name="sid" value="1001"></property>
        <property name="sname" value="张三"></property>
        <property name="age" value="23"></property>
        <property name="gender" value="男"></property>
    </bean>

    <bean id="studentThree" class="com.atguigu.spring.pojo.Student">
        <constructor-arg value="1002"></constructor-arg>
        <constructor-arg value="李四"></constructor-arg>
        <constructor-arg value="女"></constructor-arg>
        <constructor-arg value="24" name="age"></constructor-arg>
    </bean>

    <bean id="studentFour" class="com.atguigu.spring.pojo.Student">
        <property name="sid" value="1003"></property>
        <!--
            <：&lt;
            >：&gt;
            CDATA节其中的内容会原样解析<![CDATA[...]]>
            CDATA节是xml中一个特殊的标签，因此不能写在一个属性中
        -->
        <!--<property name="sname" value="&lt;王五&gt;"></property>-->
        <property name="sname">
            <value><![CDATA[<王五>]]></value>
        </property>
        <property name="gender">
            <null />
        </property>
    </bean>

    <bean id="studentFive" class="com.atguigu.spring.pojo.Student">
        <property name="sid" value="1004"></property>
        <property name="sname" value="赵六"></property>
        <property name="age" value="26"></property>
        <property name="gender" value="男"></property>
        <!--ref：引用IOC容器中的某个bean的id-->
        <!--<property name="clazz" ref="clazzOne"></property>-->
        <!--级联的方式，要保证提前为clazz属性赋值或者实例化-->
        <!--<property name="clazz.cid" value="2222"></property>
        <property name="clazz.cname" value="远大前程班"></property>-->
        <property name="clazz">
            <!--内部bean，只能在当前bean的内部使用，不能直接通过IOC容器获取-->
            <bean id="clazzInner" class="com.atguigu.spring.pojo.Clazz">
                <property name="cid" value="2222"></property>
                <property name="cname" value="远大前程班"></property>
            </bean>
        </property>
        <property name="hobby">
            <array>
                <value>抽烟</value>
                <value>喝酒</value>
                <value>烫头</value>
            </array>
        </property>
        <property name="teacherMap" ref="teacherMap"></property>
        <!--<property name="teacherMap">
            <map>
                <entry key="10086" value-ref="teacherOne"></entry>
                <entry key="10010" value-ref="teacherTwo"></entry>
            </map>
        </property>-->
    </bean>

    <bean id="clazzOne" class="com.atguigu.spring.pojo.Clazz">
        <property name="cid" value="1111"></property>
        <property name="cname" value="最强王者班"></property>
        <property name="students" ref="studentList"></property>
        <!--<property name="students">
            <list>
                <ref bean="studentOne"></ref>
                <ref bean="studentTwo"></ref>
                <ref bean="studentThree"></ref>
            </list>
        </property>-->
    </bean>

    <bean id="teacherOne" class="com.atguigu.spring.pojo.Teacher">
        <property name="tid" value="10086"></property>
        <property name="tname" value="大宝"></property>
    </bean>

    <bean id="teacherTwo" class="com.atguigu.spring.pojo.Teacher">
        <property name="tid" value="10010"></property>
        <property name="tname" value="小宝"></property>
    </bean>

    <!--配置一个集合类型的bean，需要使用util的约束-->
    <util:list id="studentList">
        <ref bean="studentOne"></ref>
        <ref bean="studentTwo"></ref>
        <ref bean="studentThree"></ref>
    </util:list>

    <util:map id="teacherMap">
        <entry key="10086" value-ref="teacherOne"></entry>
        <entry key="10010" value-ref="teacherTwo"></entry>
    </util:map>

    <bean id="studentSix" class="com.atguigu.spring.pojo.Student"
        p:sid="1005" p:sname="小明" p:teacherMap-ref="teacherMap"></bean>
</beans>

package com.atguigu.spring.test;

import com.atguigu.spring.pojo.Clazz;
import com.atguigu.spring.pojo.Person;
import com.atguigu.spring.pojo.Student;
import org.junit.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

/**
 * Date:2022/7/1
 * Author:ybc
 * Description:
 */
public class IOCByXMLTest {

    /**
     * 获取bean的三种方式：
     * 1、根据bean的id获取
     * 2、根据bean的类型获取
     * 注意：根据类型获取bean时，要求IOC容器中有且只有一个类型匹配的bean
     * 若没有任何一个类型匹配的bean，此时抛出异常：NoSuchBeanDefinitionException
     * 若有多个类型匹配的bean，此时抛出异常：NoUniqueBeanDefinitionException
     * 3、根据bean的id和类型获取
     * 结论：
     * 根据类型来获取bean时，在满足bean唯一性的前提下
     * 其实只是看：『对象 instanceof 指定的类型』的返回结果
     * 只要返回的是true就可以认定为和类型匹配，能够获取到。
     * 即通过bean的类型、bean所继承的类的类型、bean所实现的接口的类型都可以获取bean
     */

    @Test
    public void testDI(){
        //获取IOC容器
        ApplicationContext ioc = new ClassPathXmlApplicationContext("spring-ioc.xml");
        //获取bean
        Student student = ioc.getBean("studentSix", Student.class);
        System.out.println(student);
        /*Clazz clazz = ioc.getBean("clazzInner", Clazz.class);
        System.out.println(clazz);*/
        /*Clazz clazz = ioc.getBean("clazzOne", Clazz.class);
        System.out.println(clazz);*/
    }
    @Test
    public void testIOC(){
        //获取IOC容器
        ApplicationContext ioc = new ClassPathXmlApplicationContext("spring-ioc.xml");
        //获取bean
        //Student studentOne = (Student) ioc.getBean("studentOne");
        //Student student = ioc.getBean(Student.class);
        //Student student = ioc.getBean("studentOne", Student.class);
        Person person = ioc.getBean(Person.class);
        System.out.println(person);
    }
}

<bean id="studentSix" class="com.atguigu.spring.bean.Student"
      p:id="1006" p:name="小明" p:clazz-ref="clazzOne" p:teacherMap-ref="teacherMap"></bean>

<!-- MySQL驱动 -->
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>8.0.16</version>
</dependency>
<!-- 数据源 -->
<dependency>
    <groupId>com.alibaba</groupId>
    <artifactId>druid</artifactId>
    <version>1.0.31</version>
</dependency>

jdbc.user=root
jdbc.password=atguigu
jdbc.url=jdbc:mysql://localhost:3306/ssm?serverTimezone=UTC
jdbc.driver=com.mysql.cj.jdbc.Driver

<!-- 引入外部属性文件 ，每一个新的内容都需要引入新的约束，直接写resources下面的配置文件名-和配置文件一个目录，类路径-->
<context:property-placeholder location="classpath:jdbc.properties"/>

<bean id="druidDataSource" class="com.alibaba.druid.pool.DruidDataSource">
    <property name="url" value="${jdbc.url}"/>
    <property name="driverClassName" value="${jdbc.driver}"/>
    <property name="username" value="${jdbc.user}"/>
    <property name="password" value="${jdbc.password}"/>
</bean>

@Test
public void testDataSource() throws SQLException {
    ApplicationContext ac = new ClassPathXmlApplicationContext("spring-datasource.xml");
    DataSource dataSource = ac.getBean(DataSource.class);
    Connection connection = dataSource.getConnection();
    System.out.println(connection);
}

public class User {
private Integer id;
private String username;
private String password;
private Integer age;
    public User() {
    }
    public User(Integer id, String username, String password, Integer age) {
        this.id = id;
        this.username = username;
        this.password = password;
        this.age = age;
    }
    public Integer getId() {
        return id;
    }
    public void setId(Integer id) {
        this.id = id;
    }
    public String getUsername() {
        return username;
    }
    public void setUsername(String username) {
        this.username = username;
    }
    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }
    public Integer getAge() {
        return age;
    }
    public void setAge(Integer age) {
        this.age = age;
    }
    @Override
    public String toString() {
        return "User{" +
            "id=" + id +
            ", username='" + username + '\'' +
            ", password='" + password + '\'' +
            ", age=" + age +
            '}';
    }
}

<!-- scope属性：取值singleton（默认值），bean在IOC容器中只有一个实例，IOC容器初始化时创建
对象 -->
<!-- scope属性：取值prototype，bean在IOC容器中可以有多个实例，getBean()时创建对象 -->
<bean class="com.atguigu.bean.User" scope="prototype"></bean>

<bean class="com.atguigu.bean.User" scope="prototype"></bean>就不是单例了

@Test
public void testBeanScope(){
    ApplicationContext ac = new ClassPathXmlApplicationContext("spring-scope.xml");
    User user1 = ac.getBean(User.class);
    User user2 = ac.getBean(User.class);
    System.out.println(user1==user2);//true--证明默认是单例模式，设置scope="prototype"就是false
}

public class User {
    private Integer id;
    private String username;
    private String password;
    private Integer age;
    public User() {
        System.out.println("生命周期：1、创建对象");
    }
    public User(Integer id, String username, String password, Integer age) {
        this.id = id;
        this.username = username;
        this.password = password;
        this.age = age;
    }
    public Integer getId() {
        return id;
    }
    public void setId(Integer id) {
        System.out.println("生命周期：2、依赖注入（也就是赋值-随便找一个属性演示了）");
        this.id = id;
    }
    public String getUsername() {
        return username;
    }
    public void setUsername(String username) {
        this.username = username;
    }
    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }
    public Integer getAge() {
        return age;
    }
    public void setAge(Integer age) {
        this.age = age;
    }
    public void initMethod(){
        System.out.println("生命周期：3、初始化");
    }
    public void destroyMethod(){
        System.out.println("生命周期：5、销毁（4是使用，我们这里demo了）");
    }
    @Override
    public String toString() {
        return "User{" +
            "id=" + id +
            ", username='" + username + '\'' +
            ", password='" + password + '\'' +
            ", age=" + age +
            '}';
    }
}

<!-- 使用init-method属性指定初始化方法 -->
<!-- 使用destroy-method属性指定销毁方法 -->
<bean class="com.atguigu.bean.User" scope="prototype" init-method="initMethod" destroy-method="destroyMethod">
    <property name="id" value="1001"></property>
    <property name="username" value="admin"></property>
    <property name="password" value="123456"></property>
    <property name="age" value="23"></property>
</bean>

@Test
public void testLife(){
    ClassPathXmlApplicationContext ac = new ClassPathXmlApplicationContext("spring-lifecycle.xml");
    User bean = ac.getBean(User.class);
    System.out.println("生命周期：4、通过IOC容器获取bean并使用");
    ac.close();
}

package com.atguigu.spring.process;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;
public class MyBeanProcessor implements BeanPostProcessor {
    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName)
        throws BeansException {
        //此方法在bean的生命周期初始化之前执行
        System.out.println("☆☆☆" + beanName + " = " + bean);
        //所以这里返回的是bean额外操作之后的对象，不进行额外操作，直接返回 return bean也行，beanName就是bean的id
        return bean;
    }
    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName)
        throws BeansException {
        //
        System.out.println("★★★" + beanName + " = " + bean);
        return bean;
    }
}

/*
* Copyright 2002-2020 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* https://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.springframework.beans.factory;
import org.springframework.lang.Nullable;
/**
* Interface to be implemented by objects used within a {@link BeanFactory}
which
* are themselves factories for individual objects. If a bean implements this
* interface, it is used as a factory for an object to expose, not directly as a
* bean instance that will be exposed itself.
*
* <p><b>NB: A bean that implements this interface cannot be used as a normal
bean.</b>
* A FactoryBean is defined in a bean style, but the object exposed for bean
* references ({@link #getObject()}) is always the object that it creates.
*
* <p>FactoryBeans can support singletons and prototypes, and can either create
* objects lazily on demand or eagerly on startup. The {@link SmartFactoryBean}
* interface allows for exposing more fine-grained behavioral metadata.
*
* <p>This interface is heavily used within the framework itself, for example
for
* the AOP {@link org.springframework.aop.framework.ProxyFactoryBean} or the
* {@link org.springframework.jndi.JndiObjectFactoryBean}. It can be used for
* custom components as well; however, this is only common for infrastructure
code.
*
* <p><b>{@code FactoryBean} is a programmatic contract. Implementations are not
* supposed to rely on annotation-driven injection or other reflective
facilities.</b>
* {@link #getObjectType()} {@link #getObject()} invocations may arrive early in
the
* bootstrap process, even ahead of any post-processor setup. If you need access
to
* other beans, implement {@link BeanFactoryAware} and obtain them
programmatically.
*
* <p><b>The container is only responsible for managing the lifecycle of the
FactoryBean
* instance, not the lifecycle of the objects created by the FactoryBean.</b>
Therefore,
* a destroy method on an exposed bean object (such as {@link
java.io.Closeable#close()}
* will <i>not</i> be called automatically. Instead, a FactoryBean should
implement
* {@link DisposableBean} and delegate any such close call to the underlying
object.
*
* <p>Finally, FactoryBean objects participate in the containing BeanFactory's
* synchronization of bean creation. There is usually no need for internal
* synchronization other than for purposes of lazy initialization within the
* FactoryBean itself (or the like).
*
* @author Rod Johnson
* @author Juergen Hoeller
* @since 08.03.2003
* @param <T> the bean type
* @see org.springframework.beans.factory.BeanFactory
* @see org.springframework.aop.framework.ProxyFactoryBean
* @see org.springframework.jndi.JndiObjectFactoryBean
*/
public interface FactoryBean<T> {
    /**
* The name of an attribute that can be
* {@link org.springframework.core.AttributeAccessor#setAttribute set} on a
* {@link org.springframework.beans.factory.config.BeanDefinition} so that
* factory beans can signal their object type when it can't be deduced from
* the factory bean class.
* @since 5.2
*/
    String OBJECT_TYPE_ATTRIBUTE = "factoryBeanObjectType";
    /**
* Return an instance (possibly shared or independent) of the object
* managed by this factory.
* <p>As with a {@link BeanFactory}, this allows support for both the
* Singleton and Prototype design pattern.
* <p>If this FactoryBean is not fully initialized yet at the time of
* the call (for example because it is involved in a circular reference),
* throw a corresponding {@link FactoryBeanNotInitializedException}.
* <p>As of Spring 2.0, FactoryBeans are allowed to return {@code null}
* objects. The factory will consider this as normal value to be used; it
* will not throw a FactoryBeanNotInitializedException in this case anymore.
* FactoryBean implementations are encouraged to throw
* FactoryBeanNotInitializedException themselves now, as appropriate.
* @return an instance of the bean (can be {@code null})
* @throws Exception in case of creation errors
* @see FactoryBeanNotInitializedException
*/
    @Nullable
    T getObject() throws Exception;
    /**
* Return the type of object that this FactoryBean creates,
* or {@code null} if not known in advance.
* <p>This allows one to check for specific types of beans without
* instantiating objects, for example on autowiring.
* <p>In the case of implementations that are creating a singleton object,
* this method should try to avoid singleton creation as far as possible;
* it should rather estimate the type in advance.
* For prototypes, returning a meaningful type here is advisable too.
* <p>This method can be called <i>before</i> this FactoryBean has
* been fully initialized. It must not rely on state created during
* initialization; of course, it can still use such state if available.
* <p><b>NOTE:</b> Autowiring will simply ignore FactoryBeans that return
* {@code null} here. Therefore it is highly recommended to implement
* this method properly, using the current state of the FactoryBean.
* @return the type of object that this FactoryBean creates,
* or {@code null} if not known at the time of the call
* @see ListableBeanFactory#getBeansOfType
*/
    @Nullable
    Class<?> getObjectType();
    /**
* Is the object managed by this factory a singleton? That is,
* will {@link #getObject()} always return the same object
* (a reference that can be cached)?
* <p><b>NOTE:</b> If a FactoryBean indicates to hold a singleton object,
* the object returned from {@code getObject()} might get cached
* by the owning BeanFactory. Hence, do not return {@code true}
* unless the FactoryBean always exposes the same reference.
* <p>The singleton status of the FactoryBean itself will generally
* be provided by the owning BeanFactory; usually, it has to be
* defined as singleton there.
* <p><b>NOTE:</b> This method returning {@code false} does not
* necessarily indicate that returned objects are independent instances.
* An implementation of the extended {@link SmartFactoryBean} interface
* may explicitly indicate independent instances through its
* {@link SmartFactoryBean#isPrototype()} method. Plain {@link FactoryBean}
* implementations which do not implement this extended interface are
* simply assumed to always return independent instances if the
* {@code isSingleton()} implementation returns {@code false}.
* <p>The default implementation returns {@code true}, since a
* {@code FactoryBean} typically manages a singleton instance.
* @return whether the exposed object is a singleton
* @see #getObject()
* @see SmartFactoryBean#isPrototype()
*/
    //证明FactoryBean是单例
    default boolean isSingleton() {
        return true;
    }
}

public class UserFactoryBean implements FactoryBean<User> {
    @Override
    public User getObject() throws Exception {
        return new User();
    }
    @Override
    public Class<?> getObjectType() {
        return User.class;
    }
}

<bean id="user" class="com.atguigu.bean.UserFactoryBean"></bean>

@Test
public void testUserFactoryBean(){
    //获取IOC容器
    ApplicationContext ac = new ClassPathXmlApplicationContext("spring-factorybean.xml");
     User user = ac.getBean(User.class);
    System.out.println(user);
}
public class UserFactoryBean implements FactoryBean<User> {
    @Override
    public User getObject() throws Exception {
        return new User();
    }

    @Override
    public Class<?> getObjectType() {
        return User.class;
    }
}