spring（1）：基于XML获取Bean对象以及各种依赖注入方式

1. 获取Bean

XML文件：

<bean id="helloworld" class="org.kkk.spring6.bean.HelloWorld">bean>

1.1 根据id获取

@Test
public void testHelloWorld(){
    //加载XML文件
	ApplicationContext context = new ClassPathXmlApplicationContext("beans.xml");
	//根据id获取Bean对象
    HelloWorld bean = context.getBean("helloworld");
    //调用该对象的方法
    bean.sayHello();
}

1.2 根据类型获取

@Test
public void testHelloWorld(){
    //加载XML文件
	ApplicationContext context = new ClassPathXmlApplicationContext("beans.xml");
	//根据类型获取Bean对象
    HelloWorld bean = context.getBean(helloworld.class);
    //调用该对象的方法
    bean.sayHello();
}

1.3 根据id和类型获取

@Test
public void testHelloWorld(){
    //加载XML文件
	ApplicationContext context = new ClassPathXmlApplicationContext("beans.xml");
	//根据类型获取Bean对象
    HelloWorld bean = context.getBean("helloworld", helloworld.class);
    //调用该对象的方法
    bean.sayHello();
}

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。

  例如以下XML文件，当IOC容器中一共配置了两个，根据类型获取时会抛出异常。

<bean id="helloworldOne" class="org.kkk.spring6.bean.HelloWorld">bean>
<bean id="helloworldTwo" class="org.kkk.spring6.bean.HelloWorld">bean>

• 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。

  因此，如果一个接口有多个实现类，这些实现类都配置了 bean，根据接口类型就不可以获取到 bean ，因为不满足唯一性。而如果这个接口只有一个实现类，那就可以获取到。

2. 依赖注入

个人理解：依赖注入就是为对象的属性赋值

2.1 setter注入

通过组件类的setXxx()方法给组件对象设置属性

①创建学生类Student

package org.kkk.spring6.bean;

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 + '\'' +
                '}';
    }

}

②配置bean时为属性赋值

spring-di.xml

<bean id="student" class="org.kkk.spring6.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>

③测试

@Test
public void testDIBySet(){
    ApplicationContext context= new ClassPathXmlApplicationContext("spring-di.xml");
    Student student = context.getBean("student", Student.class);
    System.out.println(student);
}

2.2 构造器注入

通过组件类的有参构造方法给组件对象设置属性

①在Student类中添加有参构造

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

②配置bean

spring-di.xml

<bean id="student" class="org.kkk.spring6.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>

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 testDIByConstructor(){
    ApplicationContext context = new ClassPathXmlApplicationContext("spring-di.xml");
    Student student = context.getBean("student", Student.class);
    System.out.println(student);
}

2.3 特殊值处理

在为属性进行赋值时，可能会出现一些特殊情况要特殊处理。

①null值

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

注意：

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

以上写法，为name所赋的值是字符串null

②xml实体

<property name="expression" value="a < b"/>

③CDATA节

<property name="expression">
    
    
    
    
    <value>value>
property>

2.4 为对象类型属性赋值

当某一个类存在类型为另外一个类的属性时，就不能按照上述一般情况对这个属性赋值。例如，现在有学生类和班级类，为了表示学生和班级的关系，学生类中有一个班级类的属性。

代码表示如下：

班级类Clazz

package org.kkk.spring6.bean
    
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;
    }
}

Student类

在Student类中添加以下代码：

private Clazz clazz;

public Clazz getClazz() {
	return clazz;
}

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

可以看到，学生类中有一个属性为clazz，其类型为班级类。我们对clazz进行属性赋值，有以下几种方法。

①外部bean

配置Clazz类型的bean：

<bean id="clazz" class="org.kkk.spring6.bean.Clazz">
    <property name="clazzId" value="1001">property>
    <property name="clazzName" value="c++开发培训班">property>
bean>

为Student中的clazz属性赋值：

<bean id="student" class="org.kkk.spring6.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>
    
    <property name="clazz" ref="clazz">property>
bean>

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 ‘org.kkk.spring6.bean.Clazz’ for property ‘clazz’: no matching editors or conversion strategy 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

② 内部bean

<bean id="student" class="org.kkk.spring6.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>
    <property name="clazz">
        
        
        <bean id="clazzInner" class="org.kkk.spring6.bean.Clazz">
            <property name="clazzId" value="1001">property>
            <property name="clazzName" value="c++开发培训班">property>
        bean>
    property>
bean>

③ 级联属性赋值

<bean id="student" class="org.kkk.spring6.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>
    <property name="clazz" ref="clazzOne">property>
    <property name="clazz.clazzId" value="1001">property>
    <property name="clazz.clazzName" value="c++开发培训班">property>
bean>

2.5 为数组类型属性赋值

①修改Student类

在Student类中添加以下代码：

private String[] hobbies;

public String[] getHobbies() {
    return hobbies;
}

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

②配置bean

<bean id="student" class="org.kkk.spring.bean6.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" ref="clazz">property>
    <property name="hobbies">
        <array>
            <value>吃饭value>
            <value>睡觉value>
            <value>写代码value>
        array>
    property>
bean>

2.6 为集合类型属性赋值

①为List集合类型属性赋值

在Clazz类中添加以下代码：

private List<Student> students;

public List<Student> getStudents() {
    return students;
}

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

配置bean：

<bean id="clazz" class="org.kkk.spring6.bean.Clazz">
    <property name="clazzId" value="1002">property>
    <property name="clazzName" value="Java开发培训班">property>
    <property name="students">
        <list>
            <ref bean="studentOne">ref>
            <ref bean="studentTwo">ref>
            <ref bean="studentThree">ref>
        list>
    property>
bean>

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为Map集合类型属性赋值

创建教师类Teacher：

package org.kkk.spring6.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 + '\'' +
                '}';
    }
}

在Student类中添加以下代码：

private Map<String, Teacher> teacherMap;

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

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

配置bean：

<bean id="teacherOne" class="org.kkk.spring6.bean.Teacher">
    <property name="teacherId" value="1005">property>
    <property name="teacherName" value="大宝">property>
bean>

<bean id="teacherTwo" class="org.kkk.spring6.bean.Teacher">
    <property name="teacherId" value="1006">property>
    <property name="teacherName" value="二宝">property>
bean>

<bean id="studentFour" class="org.kkk.spring6.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>
    
    <property name="clazz" ref="clazzOne">property>
    <property name="hobbies">
        <array>
            <value>吃饭value>
            <value>睡觉value>
            <value>写代码value>
        array>
    property>
    <property name="teacherMap">
        <map>
            <entry>
                <key>
                    <value>1005value>
                key>
                <ref bean="teacherOne">ref>
            entry>
            <entry>
                <key>
                    <value>1006value>
                key>
                <ref bean="teacherTwo">ref>
            entry>
        map>
    property>
bean>

③引用集合类型的bean

<util:list id="students">
    <ref bean="studentOne">ref>
    <ref bean="studentTwo">ref>
    <ref bean="studentThree">ref>
util:list>

<util:map id="teacherMap">
    <entry>
        <key>
            <value>1005value>
        key>
        <ref bean="teacherOne">ref>
    entry>
    <entry>
        <key>
            <value>1006value>
        key>
        <ref bean="teacherTwo">ref>
    entry>
util:map>
<bean id="clazzTwo" class="org.kkk.spring6.bean.Clazz">
    <property name="clazzId" value="1002">property>
    <property name="clazzName" value="Java开发培训班">property>
    <property name="students" ref="students">property>
bean>
<bean id="studentFour" class="org.kkk.spring6.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>
    
    <property name="clazz" ref="clazzOne">property>
    <property name="hobbies">
        <array>
            <value>吃饭value>
            <value>睡觉value>
            <value>写代码value>
        array>
    property>
    <property name="teacherMap" ref="teacherMap">property>
bean>

使用util:list、util:map标签必须引入相应的命名空间

<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"
    xsi:schemaLocation="http://www.springframework.org/schema/util
    http://www.springframework.org/schema/util/spring-util.xsd
    http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans.xsd">

2.7 p命名空间

引入p命名空间

<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/util
       http://www.springframework.org/schema/util/spring-util.xsd
       http://www.springframework.org/schema/beans
       http://www.springframework.org/schema/beans/spring-beans.xsd">

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

<bean id="student" class="org.kkk.spring6.bean.Student"
    p:id="1006" p:name="小明" p:clazz-ref="clazzOne" p:teacherMap-ref="teacherMap">bean>

2.8 引入外部属性文件

①加入依赖

 
<dependency>
    <groupId>mysqlgroupId>
    <artifactId>mysql-connector-javaartifactId>
    <version>8.0.30version>
dependency>


<dependency>
    <groupId>com.alibabagroupId>
    <artifactId>druidartifactId>
    <version>1.2.15version>
dependency>

②创建外部属性文件

文件jdbc.properties保存数据库连接信息

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

③引入属性文件

引入context 名称空间

<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
       http://www.springframework.org/schema/context/spring-context.xsd">

beans>

<context:property-placeholder location="classpath:jdbc.properties"/>

注意：在使用 context:property-placeholder 元素加载外包配置文件功能前，首先需要在 XML 配置的一级标签 中添加 context 相关的约束。

④配置bean

<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>

⑤测试

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

2.9 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：

取值	含义	创建对象的时机
singleton（默认）	在IOC容器中，这个bean的对象始终为单实例	IOC容器初始化时
prototype	这个bean在IOC容器中有多个实例	获取bean时

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

取值	含义
request	在一个请求范围内有效
session	在一个会话范围内有效

②创建类User

package org.kkk.spring6.bean;
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 +
                '}';
    }
}

③配置bean

<bean class="org.kkk.spring6.bean.User" scope="prototype">bean>

④测试

@Test
public void testBeanScope(){
    ApplicationContext context = new ClassPathXmlApplicationContext("spring-scope.xml");
    User user1 = context.getBean(User.class);
    User user2 = context.getBean(User.class);
    System.out.println(user1==user2);
}

如果将scope属性设置为singleton（单例）时，那么user1与user2的地址相同，两者实质上是同一个实例对象。如果scope属性为prototype（多例），那么user1与user2的地址不同。

2.10 基于xml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

package org.kkk.spring6.autowire.controller
public class UserController {

    private UserService userService;

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

    public void saveUser(){
        userService.saveUser();
    }

}

创建接口UserService

package org.kkk.spring6.autowire.service
public interface UserService {

    void saveUser();

}

创建类UserServiceImpl实现接口UserService

package org.kkk.spring6.autowire.service.impl
public class UserServiceImpl implements UserService {

    private UserDao userDao;

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

    @Override
    public void saveUser() {
        userDao.saveUser();
    }

}

创建接口UserDao

package org.kkk.spring6.autowire.dao
public interface UserDao {

    void saveUser();

}

创建类UserDaoImpl实现接口UserDao

package org.kkk.spring6.autowire.dao.impl
public class UserDaoImpl implements UserDao {

    @Override
    public void saveUser() {
        System.out.println("保存成功");
    }

}

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="userController" class="org.kkk.spring6.autowire.controller.UserController" autowire="byType">bean>

<bean id="userService" class="org.kkk.spring6.autowire.service.impl.UserServiceImpl" autowire="byType">bean>

<bean id="userDao" class="org.kkk.spring6.autowire.dao.impl.UserDaoImpl">bean>

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="userController" class="org.kkk.spring6.autowire.controller.UserController" autowire="byName">bean>

<bean id="userService" class="org.kkk.spring6.autowire.service.impl.UserServiceImpl" autowire="byName">bean>
<bean id="userServiceImpl" class="org.kkk.spring6.autowire.service.impl.UserServiceImpl" autowire="byName">bean>

<bean id="userDao" class="org.kkk.spring6.autowire.dao.impl.UserDaoImpl">bean>
<bean id="userDaoImpl" class="org.kkk.spring6.autowire.dao.impl.UserDaoImpl">bean>

③测试

@Test
public void testAutoWireByXML(){
    ApplicationContext context = new ClassPathXmlApplicationContext("autowire-xml.xml");
    UserController userController = context.getBean(UserController.class);
    userController.saveUser();
}