3、基于XML管理bean_idea从xml生层bean

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【尚硅谷】SSM框架全套教程-讲师：杨博超

但行好事，莫问前程

3、基于XML管理bean

实验一：入门案例

1 创建Maven Module

略

2 引入依赖

<!-- 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>5.3.22</version>
</dependency>
<!-- junit测试 -->
<dependency>
    <groupId>junit</groupId>
    <artifactId>junit</artifactId>
    <version>4.12</version>
    <scope>test</scope>
</dependency>
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3 创建类HelloWorld

public class HelloWorld {

    public void sayHello() {
        System.out.println("HelloWorld");
    }
}
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4 创建Spring的配置文件

5 在Spring的配置文件中配置bean

<?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">
    
	<!--
	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="pers.tianyu.bean.HelloWorld"></bean>
</beans>
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6 创建测试类测试

@Test
public void testSayHelloById(){
    ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
    HelloWorld bean = (HelloWorld) context.getBean("helloWorld");
    bean.sayHello();
}
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7 思路

8 注意

Spring 底层默认通过反射技术调用组件类的无参构造器来创建组件对象，这一点需要注意。

如果在需要无参构造器时，没有无参构造器，则会抛出下面的异常：

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>
()
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实验二：获取bean

1 方式一：根据id获取

由于 id 属性指定了 bean 的唯一标识，所以根据 bean 标签的 id 属性可以精确获取到一个组件对象。

上个实验中我们使用的就是这种方式。

2 方式二：根据类型获取

@Test
public void testSayHelloByType(){
    ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
    HelloWorld bean = context.getBean(HelloWorld.class);
    bean.sayHello();
}
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3 方式三：根据id和类型

@Test
public void testSayHelloByIdByType(){
    ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
    HelloWorld bean = context.getBean("helloWorld", HelloWorld.class);
    bean.sayHello();
}
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4 注意

当根据类型获取bean时，要求IOC容器中指定类型的bean有且只能有一个

当IOC容器中一共配置了两个：

<bean id="helloWorldOne" class="pers.tianyu.bean.HelloWorld"></bean>
<bean id="helloWorldTwo" class="pers.tianyu.bean.HelloWorld"></bean>
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根据类型获取时会抛出异常：

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
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5 扩展

如果组件类实现了接口，根据接口类型可以获取 bean 吗？

可以，前提是bean唯一

@Test
public void testBImplA(){
    // A：接口 有一个方法sayA待实现
    // B：实现类 实现接口A，并在spring的XML文件中配置bean
    ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
    // 在获取类型时写A.class
    A b = context.getBean(A.class);
    b.sayA();
}
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如果一个接口有多个实现类，这些实现类都配置了 bean，根据接口类型可以获取 bean 吗？

不行，因为bean不唯一

@Test
public void testBImplAC(){
    // A：接口 有一个方法sayA待实现
    // B：实现类 实现接口A，并在spring的XML文件中配置bean
    // C：实现类 实现接口A，并在spring的XML文件中配置bean
    ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
    // 在获取类型时写A.class
    A b = context.getBean(A.class);
    b.sayA(); // 报错，如果加id就不报错
}
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6 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。

实验三：依赖注入之setter注入

1 创建学生类Student

public class Student {
    private Integer id;
    private String name;
    private Integer age;
    private String sex;
    
    // 无参有参构造函数
    // setget方法
    // toString方法
}
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2 配置bean时为属性赋值

<bean id="studentSet" class="pers.tianyu.bean.Student">
    <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>
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3 测试

@Test
public void testDIBySet() {
    ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
    Student bean = context.getBean("studentSet",Student.class);
    System.out.println(bean);
}
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实验四：依赖注入之构造器注入

1 在Student类中添加有参构造

public class Student {
    private Integer id;
    private String name;
    private Integer age;
    private String sex;
    
    // 无参有参构造函数
    // setget方法
    // toString方法
}
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2 配置bean

<bean id="studentConstructor" class="pers.tianyu.bean.Student">
    <constructor-arg value="1003"></constructor-arg>
    <constructor-arg value="李四"></constructor-arg>
    <constructor-arg value="30"></constructor-arg>
    <constructor-arg value="女"></constructor-arg>
</bean>
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注意

• constructor-arg标签还有两个属性可以进一步描述构造器参数：
  • index属性：指定参数所在位置的索引（从0开始）
  • name属性：指定参数名

3 测试

@Test
public void testDIBySet() {
    ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
    Student bean = context.getBean("studentConstructor",Student.class);
    System.out.println(bean);
}
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实验五：特殊值处理

1 字面量赋值

什么是字面量？

int a = 10;

声明一个变量a，初始化为10，此时a就不代表字母a了，而是作为一个变量的名字。

当我们引用a的时候，我们实际上拿到的值是10。

而如果a是带引号的：‘a’，那么它现在不是一个变量，它就是代表a这个字母本身，这就是字面量。

所以字面量没有引申含义，就是我们看到的这个数据本身。

<!-- 使用value属性给bean的属性赋值时，Spring会把value属性的值看做字面量 -->
<property name="name" value="张三"/>
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2 null值

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

<property name="name" value="null"></property>
1

以上写法，为name所赋的值是字符串’null’

3 xml实体

实体是对数据的引用，根据实体种类的不同，XML 解析器将使用实体的替代文本或者外部文档的内容来替代实体引用。

• 介绍以下几种常用实体
  • ' 是一个撇号：’
  • & 是一个与字符：&
  • " 是一个引号："
  • &lt; 是一个小于号：<
  • &gt; 是一个大于号：>

<!-- 如果想写<王五>，大于、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="name" value="&lt;王五&gt;"/>
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4 CDATA节

<property name="name">
<!-- 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 -->
<!-- idea快捷键CD -->
<value><![CDATA[ <王五> ]></value>
</property>
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实验六：类（类型）属性赋值

1 创建班级类Clazz

public class Clazz {
    private Integer clazzId;
    private String ClassName;

    // 无参有参构造函数
    // setget方法
    // toString方法
}
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2 修改Student类

在Student类中添加Clazz类型，并添加set、get方法。

private Clazz clazz;

public Clazz getClazz() {
	return clazz;
}
public void setClazz(Clazz clazz) {
	this.clazz = clazz;
}
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3 方式一：引用外部已声明的bean

配置Clazz类型的bean

<bean id="clazzOne" class="pers.tianyu.bean.Clazz">
    <property name="clazzId" value="1904"></property>
    <property name="className" value="1904班"></property>
</bean>
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为Student中的clazz属性赋值

<bean id="studentOne" class="pers.tianyu.bean.Student">
    <constructor-arg value="1003"></constructor-arg>
    <constructor-arg value="李四"></constructor-arg>
    <constructor-arg value="30"></constructor-arg>
    <constructor-arg value="女"></constructor-arg>
    <!-- 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>
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错误演示

<bean id="studentOne" class="pers.tianyu.bean.Student">
    <constructor-arg value="1003"></constructor-arg>
    <constructor-arg value="李四"></constructor-arg>
    <constructor-arg value="30"></constructor-arg>
    <constructor-arg value="女"></constructor-arg>
    <!-- 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" value="clazzOne"></property>
</bean>
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如果错把ref属性写成了value属性，会抛出异常：
Caused by: java.lang.IllegalStateException:Cannot convert value of type ‘java.lang.String’ to required type ‘com.atguigu.spring.bean.Clazz’ for property ‘clazz’: no matching editors or conversionstrategy found

意思是不能把String类型转换成我们要的Clazz类型，说明我们使用value属性时，Spring只把这个属性看做一个普通的字符串，不会认为这是一个bean的id，更不会根据它去找到bean来赋值。

4 方式二：内部bean

<bean id="studentOne" class="pers.tianyu.bean.Student">
    <constructor-arg value="1003"></constructor-arg>
    <constructor-arg value="李四"></constructor-arg>
    <constructor-arg value="30"></constructor-arg>
    <constructor-arg value="女"></constructor-arg>
    <!-- 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IOC容器获取，因此可以省略id属性 -->
    <property name="clazz">
        <bean name="clazzInner" class="pers.tianyu.bean.Clazz">
            <property name="clazzId" value="1908"></property>
            <property name="className" value="1908班"></property>
        </bean>
    </property>
</bean>
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5 方式三：级联属性赋值

<bean id="studentOne" class="pers.tianyu.bean.Student">
    <constructor-arg value="1003"></constructor-arg>
    <constructor-arg value="李四"></constructor-arg>
    <constructor-arg value="30"></constructor-arg>
    <constructor-arg value="女"></constructor-arg>
    <!-- 一定先引用某个bean为属性赋值，才可以使用级联方式更新属性 -->
    <property name="clazz" ref="clazzOne"></property>
    <property name="clazz.clazzId" value="2222"></property>
    <property name="clazz.className" value="2222班"></property>
</bean>
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实验七：数组（类型）属性赋值

1 修改Student类

添加数组类型属性，添加set、get方法。

private String[] hobbies;

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

<bean id="studentOne" class="pers.tianyu.bean.Student">
    <constructor-arg value="1003"></constructor-arg>
    <constructor-arg value="李四"></constructor-arg>
    <constructor-arg value="30"></constructor-arg>
    <constructor-arg value="女"></constructor-arg>
    <!-- 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>
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实验八：集合（类型）属性赋值

1 List集合类型属性赋值

在Clazz类中添加集合类型属性，添加set、get方法。

private List<Student> students;

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

<bean id="clazzOne" class="pers.tianyu.bean.Clazz">
    <property name="clazzId" value="1904"></property>
    <property name="className" value="1904班"></property>
    <property name="students">
        <list>
            <ref bean="studentOne"></ref>
        </list>
    </property>
</bean>
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注意

若为Set集合类型属性赋值，只需要将其中的list标签改为set标签即可

2 Map集合类型属性赋值

创建教师类Teacher

public class Teacher {
    private Integer teacherId;
    private String teacherName;
    // 有参无参构造函数
    // setget方法
    // toString方法
}
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在Student类中添加map类型属性，添加set、get方法。

private Map<String, Teacher> teacherMap;

public Map<String, Teacher> getTeacherMap() {
	return teacherMap;
}

public void setTeacherMap(Map<String, Teacher> teacherMap) {
	this.teacherMap = teacherMap;
}
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配置bean

<bean id="thacherOne" class="pers.tianyu.bean.Teacher">
    <property name="teacherId" value="1001"></property>
    <property name="teacherName" value="深田永美"></property>
</bean>
<bean id="thacherTwo" class="pers.tianyu.bean.Teacher">
    <property name="teacherId" value="1002"></property>
    <property name="teacherName" value="周淑怡"></property>
</bean>
<bean id="studentThree" class="pers.tianyu.bean.Student">
    <property name="id" value="1004"></property>
    <property name="name" value="王五"></property>
    <property name="age" value="26"></property>
    <property name="sex" value="女"></property>
    <property name="hobbies">
        <list>
            <value>抽烟</value>
            <value>喝酒</value>
            <value>烫头</value>
        </list>
    </property>
    <property name="teacherMap">
        <map>
            <entry>
                <key><value>1001</value></key>
                <ref bean="thacherOne"></ref>
            </entry>
            <entry>
                <key><value>1002</value></key>
                <ref bean="thacherTwo"></ref>
            </entry>
        </map>
    </property>
</bean>
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3 引用集合类型的bean

在bean中property标签写ref引用id即可。

<!--list集合类型的bean-->
<util:list id="students">
    <ref bean="studentOne"></ref>
    <ref bean="studentThree"></ref>
</util:list>

<!--map集合类型的bean-->
<util:map id="teacherMap">
    <entry>
        <key> <value>1001</value></key>
        <ref bean="thacherOne"></ref>
    </entry>
    <entry>
        <key><value>1002</value></key>
        <ref bean="thacherTwo"></ref>
    </entry>
</util:map>
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注意

使用util:list、util:map标签必须引入相应的命名空间，可以通过idea的提示功能选择

实验九：p命名空间

引入p命名空间后，可以通过以下方式为bean的各个属性赋值

set方法注入

<!--C(构造: Constructor)命名空间 , 属性依然要设置set方法-->
<!--xmlns:p="http://www.springframework.org/schema/p" -->
<bean id="teacherThree" class="pers.tianyu.pojo.Teacher"
      p:teacherId="1003" p:teacherName="三上悠亚">
</bean>
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实验十：c命名空间

构造器注入

<!--C(构造: Constructor)命名空间 , 属性依然要设置set方法-->
<!--xmlns:c="http://www.springframework.org/schema/c"-->
<bean id="teacherFour" class="pers.tianyu.pojo.Teacher"
      c:teacherId="1004" c:teacherName="饭岛爱">
</bean>
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注意

必须有有参构造、set方法，缺一不可。

实验十一：引入外部属性文件

1 加入依赖

<!-- 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>
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2 创建外部属性文件

jdbc.properties

jdbc.driverClassName=com.mysql.cj.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/mybatis?userUnicode=true&characterEncoding=utf8&useSSL=true&serverTimezone=GMT%2B8
jdbc.username=root
jdbc.password=root
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3 引入属性文件

<!-- 引入外部属性文件 -->
<context:property-placeholder location="classpath:jdbc.properties"></context:property-placeholder>
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4 配置bean

<!--配置Druid数据源-->
<bean id="dataSource" class="com.alibaba.druid.pool.DruidDataSource">
    <property name="driverClassName" value="${jdbc.driverClassName}"/>
    <property name="url" value="${jdbc.url}"/>
    <property name="username" value="${jdbc.username}"/>
    <property name="password" value="${jdbc.password}"/>
</bean>
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5 测试

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

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实验十二：bean的作用域

1 概念

在Spring中可以通过配置bean标签的scope属性来指定bean的作用域范围，各取值含义参加下表：

如果是在WebApplicationContext环境下还会有另外两个作用域（但不常用）：

2 创建类User

public class User {
    private Integer id;
    private String username;
    private String password;
    private Integer age;
	// 有参无参构造方法
	// setget方法
	// toString方法
}
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3 配置bean

<!-- 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 id="User" class="pers.tianyu.pojo.User" scope="singleton">
    <property name="id" value="1001"></property>
    <property name="username" value="张三"></property>
</bean>
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4 测试

@Test
public void test03() {
    ApplicationContext context = new ClassPathXmlApplicationContext("spring-scope.xml");
    User user1 = context.getBean(User.class);
    User user2 = context.getBean(User.class);
    System.out.println(user1 == user2);
}
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实验十三：bean的生命周期

1 具体的生命周期过程

• bean对象创建（调用无参构造器）
• 给bean对象设置属性
• bean对象初始化之前操作（由bean的后值处理器中前置方法负责）
• bean对象初始化（需在配置bean时指定初始化方法）
• bean对象初始化之后操作（由bean的后置处理器后置方法负责）
• bean对象就绪可以使用
• bean对象销毁（需在配置bean时指定销毁方法）
• IOC容器关闭

2 修改类User

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 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");
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        System.out.println("生命周期：2、依赖注入");
        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 +
                '}';
    }
}
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注意

其中的initMethod()和destroyMethod()，可以通过配置bean指定为初始化和销毁的方法

3 配置bean

<bean id="User" class="pers.tianyu.bean.User" init-method="initMethod" destroy-method="destroyMethod">
    <property name="id" value="1001"></property>
    <property name="username" value="张三"></property>
</bean>
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4 测试

@Test
public void test04(){
    // 不能使用ApplicationContext，它没有close()方法
    ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("spring-scope.xml");
    User bean = context.getBean(User.class);
    System.out.println(bean);
    context.close();
}
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8

5 bean的后置处理器

bean的后置处理器会在生命周期的初始化前后添加额外的操作，需要实现BeanPostProcessor接口，且配置到IOC容器中，需要注意的是，bean后置处理器不是单独针对某一个bean生效，而是针对IOC容器中所有bean都会执行

创建bean的后置处理器：

public class MyBeanPostProcessor 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("生命周期：4、前置");
        return bean;
    }

    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        // 此方法在bean的生命周期初始化之后执行
        System.out.println("生命周期：4、后置");
        return bean;
    }
}
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在IOC容器中配置后置处理器：

<!-- bean的后置处理器要放入IOC容器才能生效 -->
<bean id="beanPostProcessor" class="pers.tianyu.process.MyBeanPostProcessor"></bean>
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2

实验十四：FactoryBean

1 简介

FactoryBean是Spring提供的一种整合第三方框架的常用机制。

与普通的bean不同，配置一个FactoryBean类型的bean，在获取bean的时候得到的并不是class属性中配置的这个类的对象，而是getObject()方法的返回值。

通过这种机制，Spring可以帮我们把复杂组件创建的详细过程和繁琐细节都屏蔽起来，只把最简洁的使用界面展示给我们。

将来我们整合Mybatis时，Spring就是通过FactoryBean机制来帮我们创建SqlSessionFactory对象的。

/*
* 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()
	*/
	default boolean isSingleton() {
		return true;
	}
}
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2 创建类UserFactoryBean

getObject()：通过一个对象交给IOC容器管理
getObjectType()：设置所提供对象的类型
isSingleton()：所提供对象是否单例

public class UserFactoryBean implements FactoryBean<User> {

    @Override
    public User getObject() throws Exception {
        return new User();
    }

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

<bean class="pers.tianyu.Factory.UserFactoryBean"/>
1

4 测试

@Test
public void test05(){
    ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("spring-scope.xml");
    User bean = context.getBean(User.class);
    System.out.println(bean);
}
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实验十五：基于xml的自动装配

自动装配：

根据指定的策略，在IOC容器中匹配某一个bean，自动为指定的bean中所依赖的类类型或接口类型属性赋值

1 场景模拟

创建类UserController

public class UserController {
    private UserService userService;

    public void setUserService(UserService userService) {
        this.userService = userService;
    }

    public void saveUser() {
        userService.saveUser();
    }
}
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创建接口UserService

public interface UserService {
    void saveUser();
}
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3

创建类UserServiceImpl实现接口UserService

public class UserServiceImpl implements UserService {
    private UserDao userDao;

    public void setUserDao(UserDao userDao) {
        this.userDao = userDao;
    }

    @Override
    public void saveUser() {
        userDao.saveUser();
    }
}
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创建接口UserDao

public interface UserDao {
    void saveUser();
}
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创建类UserDaoImpl实现接口UserDao

public class UserDaoImpl implements UserDao {
    @Override
    public void saveUser() {
        System.out.println("保存成功");
    }
}
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2 配置bean

使用bean标签的autowire属性设置自动装配效果

自动装配方式：byType

byType：根据类型匹配IOC容器中的某个兼容类型的bean，为属性自动赋值
若在IOC中，没有任何一个兼容类型的bean能够为属性赋值，则该属性不装配，即值为默认值null
若在IOC中，有多个兼容类型的bean能够为属性赋值，则抛出异常NoUniqueBeanDefinitionException

<bean id="controller" class="pers.tianyu.controller.UserController" autowire="byType"></bean>
<bean id="service" class="pers.tianyu.service.impl.UserServiceImpl" autowire="byType"></bean>
<bean id="dao" class="pers.tianyu.dao.impl.UserDaoImpl"></bean>
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自动装配方式：byName

byName：将自动装配的属性的属性名，作为bean的id在IOC容器中匹配相对应的bean进行赋值

<bean id="controller" class="pers.tianyu.controller.UserController" autowire="byName"></bean>
<bean id="userService" class="pers.tianyu.service.impl.UserServiceImpl" autowire="byName"></bean>
<bean id="userDao" class="pers.tianyu.dao.impl.UserDaoImpl"></bean>
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3 测试

@Test
public void test06() {
    ApplicationContext context = new ClassPathXmlApplicationContext("autowrite.xml");
    UserController bean = context.getBean(UserController.class);
    bean.saveUser();
}
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