瓜瓜头条

4、Spring之依赖注入

2023-08-02 08:38 由 Javaer1995 发表于 #后端开发

依赖注入就是对类的属性进行赋值

4.1、环境搭建

创建名为spring_ioc_xml的新module，过程参考3.1节

4.1.1、创建spring配置文件

<?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">

</beans>

4.1.2、创建学生类Student

package org.rain.spring.pojo;

/**
 * @author liaojy
 * @date 2023/7/27 - 22:33
 */
public class Student {

    private Integer id;
    private String name;
    private Integer age;
    private String sex;

    public Student() {
    }

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

    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 + '\'' +
                '}';
    }
}

4.2、setter注入(常用)

4.2.1、配置bean

    <!--
        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
            value属性：设置属性值
    -->
    <bean id="student" class="org.rain.spring.pojo.Student">
        <property name="id" value="0011"></property>
        <property name="name" value="张三"></property>
        <property name="age" value="23"></property>
        <property name="sex" value="男"></property>
    </bean>

4.2.2、测试

package org.rain.spring.test;

import org.junit.Test;
import org.rain.spring.pojo.Student;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

/**
 * @author liaojy
 * @date 2023/7/27 - 22:43
 */
public class IOCByXmlTest {

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

4.3、构造器注入

4.3.1、配置bean

注意：constructor-arg标签的数量，必须和某一个构造器方法的参数数量一致

    <!--
        constructor标签：通过组件类的有参构造方法给组件对象设置属性
            name属性：指定有参构造方法参数名
            value属性：设置有参构造方法参数值
    -->
    <bean id="studentTwo" class="org.rain.spring.pojo.Student">
        <constructor-arg name="id" value="1002"></constructor-arg>
        <constructor-arg name="name" value="李四"></constructor-arg>
        <constructor-arg name="age" value="24"></constructor-arg>
        <constructor-arg name="sex" value="女"></constructor-arg>
    </bean>

4.3.2、测试

    @Test
    public void testDIConstructor(){
        ApplicationContext applicationContext = new ClassPathXmlApplicationContext("spring-ioc.xml");
        Student student = applicationContext.getBean("studentTwo", Student.class);
        System.out.println(student);
    }

4.4、特殊值处理

4.4.1、null值

4.4.1.1、配置bean

注意：该<property name="sex" value="null">写法，实际为sex所赋的值是字符串null

    <bean id="studentThree" class="org.rain.spring.pojo.Student">
        <property name="id" value="1003"></property>
        <property name="name" value="张三"></property>
        <property name="sex" >
            <null></null>
        </property>
    </bean>

4.4.1.2、测试

由控制台日志可知，此时sex的值为null

    @Test
    public void testDIspecial(){
        ApplicationContext applicationContext = new ClassPathXmlApplicationContext("spring-ioc.xml");
        Student student = applicationContext.getBean("studentThree", Student.class);
        System.out.println(student.getSex().toString());
    }

+++++++++++++++++++++++++++++++++++分割线+++++++++++++++++++++++++++++++++++

由控制台日志可知，此时age的值也为null；所以不配置属性也能实现同样的效果

4.4.2、xml字符值

4.4.2.1、方式一：实体

    <bean id="studentThree" class="org.rain.spring.pojo.Student">
        <property name="id" value="1003"></property>
        <!--用实体来代替xml字符-->
        <property name="name" value="&lt;张三&gt;"></property>
        <property name="sex" >
            <null></null>
        </property>
    </bean>

4.4.2.2、方式二：CDATA节

    <bean id="studentThree" class="org.rain.spring.pojo.Student">
        <property name="id" value="1003"></property>
        <!-- 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 -->
        <property name="name">
            <value><![CDATA[<张三>]]></value>
        </property>
        <property name="sex" >
            <null></null>
        </property>
    </bean>

4.4.2.3、测试

4.5、为类类型的属性赋值

4.5.1、方式一：外部bean（常用）

4.5.1.1、创建班级类Clazz

package org.rain.spring.pojo;

/**
 * @author liaojy
 * @date 2023/7/28 - 7:54
 */
public class Clazz {
    private Integer cid;
    private String cname;

    public Clazz() {
    }

    public Clazz(Integer cid, String cname) {
        this.cid = cid;
        this.cname = cname;
    }

    public Integer getCid() {
        return cid;
    }

    public void setCid(Integer cid) {
        this.cid = cid;
    }

    public String getCname() {
        return cname;
    }

    public void setCname(String cname) {
        this.cname = cname;
    }

    @Override
    public String toString() {
        return "Clazz{" +
                "cid=" + cid +
                ", cname='" + cname + '\'' +
                '}';
    }
}

4.5.1.2、修改Student类

package org.rain.spring.pojo;

/**
 * @author liaojy
 * @date 2023/7/27 - 22:33
 */
public class Student {

    private Integer id;
    private String name;
    private Integer age;
    private String sex;

    private Clazz clazz;

    public Student() {
    }

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

    public Clazz getClazz() {
        return clazz;
    }

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

    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 + '\'' +
                ", clazz=" + clazz +
                '}';
    }
}

4.5.1.3、配置外部bean

    <bean id="clazz" class="org.rain.spring.pojo.Clazz">
        <property name="cid" value="1111"></property>
        <property name="cname" value="三年E班"></property>
    </bean>

4.5.1.4、引用外部bean

    <bean id="studentfour" class="org.rain.spring.pojo.Student">
        <property name="id" value="0011"></property>
        <property name="name" value="张三"></property>
        <property name="age" value="23"></property>
        <property name="sex" value="男"></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="clazz"></property>
    </bean>

4.5.1.5、测试

    @Test
    public void testDIOuterBean(){
        ApplicationContext applicationContext = new ClassPathXmlApplicationContext("spring-ioc.xml");
        Student student = applicationContext.getBean("studentfour", Student.class);
        System.out.println(student);
    }

4.5.2、方式二、级联

4.5.2.1、配置bean

    <bean id="clazz" class="org.rain.spring.pojo.Clazz">
        <property name="cid" value="1111"></property>
        <property name="cname" value="三年E班"></property>
    </bean>


    <bean id="studentFive" class="org.rain.spring.pojo.Student">
        <property name="id" value="0011"></property>
        <property name="name" value="张三"></property>
        <property name="age" value="23"></property>
        <property name="sex" value="男"></property>
        <!-- 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="clazz"></property>
        <property name="clazz.cid" value="2222"></property>
        <property name="clazz.cname" value="五年A班"></property>
    </bean>

4.5.2.2、测试

    @Test
    public void testDICascade(){
        ApplicationContext applicationContext = new ClassPathXmlApplicationContext("spring-ioc.xml");
        Student student = applicationContext.getBean("studentFive", Student.class);
        System.out.println(student);
    }

4.5.3、内部bean（常用）

4.5.3.1、配置bean

    <bean id="studentSix" class="org.rain.spring.pojo.Student">
        <property name="id" value="0011"></property>
        <property name="name" value="张三"></property>
        <property name="age" value="23"></property>
        <property name="sex" value="男"></property>
        <property name="clazz">
            <!-- 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 -->
            <bean class="org.rain.spring.pojo.Clazz">
                <property name="cid" value="1111"></property>
                <property name="cname" value="三年E班"></property>
            </bean>
        </property>
    </bean>

4.5.3.2、测试

    @Test
    public void testDIInnerBean(){
        ApplicationContext applicationContext = new ClassPathXmlApplicationContext("spring-ioc.xml");
        Student student = applicationContext.getBean("studentSix", Student.class);
        System.out.println(student);
    }

4.6、为数组类型的属性赋值

4.6.1、修改Student类

在Student类中添加或修改以下代码：

    private String hobby[];

    public String[] getHobby() {
        return hobby;
    }

    public void setHobby(String[] hobby) {
        this.hobby = hobby;
    }

    @Override
    public String toString() {
        return "Student{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", age=" + age +
                ", sex='" + sex + '\'' +
                ", clazz=" + clazz +
                ", hobby=" + Arrays.toString(hobby) +
                '}';
    }

4.6.2、配置bean

    <bean id="studentSeven" class="org.rain.spring.pojo.Student">
        <property name="id" value="0011"></property>
        <property name="name" value="张三"></property>
        <property name="age" value="23"></property>
        <property name="sex" value="男"></property>
        <property name="clazz">
            <bean class="org.rain.spring.pojo.Clazz">
                <property name="cid" value="1111"></property>
                <property name="cname" value="三年E班"></property>
            </bean>
        </property>
        <property name="hobby">
            <array>
                <!--如果数组类型是基本类型和string类型，就用value标签-->
                <!--如果数组类型是类类型，就用ref标签-->
                <value>游泳</value>
                <value>跑步</value>
                <value>骑车</value>
            </array>
        </property>
    </bean>

4.6.3、测试

    @Test
    public void testDIArray(){
        ApplicationContext applicationContext = new ClassPathXmlApplicationContext("spring-ioc.xml");
        Student student = applicationContext.getBean("studentSeven", Student.class);
        System.out.println(student);
    }

4.7、为List集合类型的属性赋值

4.7.1、修改Clazz类

在Clazzt类中添加或修改以下代码：


    private List<Student> students;

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

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


    @Override
    public String toString() {
        return "Clazz{" +
                "cid=" + cid +
                ", cname='" + cname + '\'' +
                ", students=" + students +
                '}';
    }

4.7.2、配置bean

    <bean id="student" class="org.rain.spring.pojo.Student">
        <property name="id" value="0011"></property>
        <property name="name" value="张三"></property>
        <property name="age" value="23"></property>
        <property name="sex" value="男"></property>
    </bean>

    <bean id="studentThree" class="org.rain.spring.pojo.Student">
        <property name="id" value="1003"></property>
        <property name="name">
            <value><![CDATA[<张三>]]></value>
        </property>
        <property name="sex" >
            <null></null>
        </property>
    </bean>

    <bean id="clazz" class="org.rain.spring.pojo.Clazz">
        <property name="cid" value="1111"></property>
        <property name="cname" value="三年E班"></property>
    </bean>

    <bean id="studentfour" class="org.rain.spring.pojo.Student">
        <property name="id" value="0011"></property>
        <property name="name" value="张三"></property>
        <property name="age" value="23"></property>
        <property name="sex" value="男"></property>
        <property name="clazz" ref="clazz"></property>
    </bean>

    <bean id="clazzTwo" class="org.rain.spring.pojo.Clazz">
        <property name="cid" value="1111"></property>
        <property name="cname" value="三年E班"></property>
        <property name="students">
            <list>
                <!--如果list集合元素是基本类型和string类型，就用value标签-->
                <!--如果list集合元素是类类型，就用ref标签-->
                <ref bean="student"></ref>
                <ref bean="studentThree"></ref>
                <ref bean="studentfour"></ref>
            </list>
        </property>
    </bean>

4.7.3、测试

    @Test
    public void testDIList(){
        ApplicationContext applicationContext = new ClassPathXmlApplicationContext("spring-ioc.xml");
        Clazz clazz = applicationContext.getBean("clazzTwo", Clazz.class);
        System.out.println(clazz);
    }

4.8、为Map集合类型的属性赋值

4.8.1、创建教师类Teacher

package org.rain.spring.pojo;

/**
 * @author liaojy
 * @date 2023/7/30 - 12:10
 */
public class Teacher {
    private Integer tid;
    private String tname;

    public Teacher() {
    }

    public Teacher(Integer tid, String tname) {
        this.tid = tid;
        this.tname = tname;
    }

    public Integer getTid() {
        return tid;
    }

    public void setTid(Integer tid) {
        this.tid = tid;
    }

    public String getTname() {
        return tname;
    }

    public void setTname(String tname) {
        this.tname = tname;
    }

    @Override
    public String toString() {
        return "Teacher{" +
                "tid=" + tid +
                ", tname='" + tname + '\'' +
                '}';
    }
}

4.8.2、修改Student类

在Student类中添加或修改以下代码：

    private Map<String,Teacher> teacherMap;

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

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

    @Override
    public String toString() {
        return "Student{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", age=" + age +
                ", sex='" + sex + '\'' +
                ", clazz=" + clazz +
                ", hobby=" + Arrays.toString(hobby) +
                ", teacherMap=" + teacherMap +
                '}';
    }

4.8.3、配置bean

    <bean id="teacherOne" class="org.rain.spring.pojo.Teacher">
        <property name="tid" value="10010"></property>
        <property name="tname" value="张老师"></property>
    </bean>

    <bean id="teacherTwo" class="org.rain.spring.pojo.Teacher">
        <property name="tid" value="10086"></property>
        <property name="tname" value="李老师"></property>
    </bean>

    <bean id="studentEight" class="org.rain.spring.pojo.Student">
        <property name="id" value="0011"></property>
        <property name="name" value="张三"></property>
        <property name="age" value="23"></property>
        <property name="sex" value="男"></property>
        <property name="clazz">
            <bean class="org.rain.spring.pojo.Clazz">
                <property name="cid" value="1111"></property>
                <property name="cname" value="三年E班"></property>
            </bean>
        </property>
        <property name="hobby">
            <array>
                <value>游泳</value>
                <value>跑步</value>
                <value>骑车</value>
            </array>
        </property>
        <property name="teacherMap">
            <map>
                <!--如果键是字面量，就用key属性，否则用key-ref属性 -->
                <!--如果值是字面量，就用value属性，否则用value-ref属性 -->
                <entry key="10010" value-ref="teacherOne"></entry>
                <entry key="10086" value-ref="teacherTwo"></entry>
            </map>
        </property>
    </bean>

4.8.4、测试

    @Test
    public void testDIMap(){
        ApplicationContext applicationContext = new ClassPathXmlApplicationContext("spring-ioc.xml");
        Student student = applicationContext.getBean("studentEight", Student.class);
        System.out.println(student);
    }

4.9、为集合类型的属性赋值(解耦引用方式)

4.9.1、配置bean

注意：使用util:list、util:map标签必须引入相应的XML命名空间

<?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"
       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">

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

    <!--map集合类型的bean-->
    <util:map id="teacherMap">
        <entry key="10010" value-ref="teacherOne"></entry>
        <entry key="10086" value-ref="teacherTwo"></entry>
    </util:map>

    <bean id="studentNine" class="org.rain.spring.pojo.Student">
        <property name="id" value="0011"></property>
        <property name="name" value="张三"></property>
        <property name="age" value="23"></property>
        <property name="sex" value="男"></property>
        <property name="clazz">
            <bean class="org.rain.spring.pojo.Clazz">
                <property name="cid" value="1111"></property>
                <property name="cname" value="三年E班"></property>
            </bean>
        </property>
        <property name="hobby">
            <array>
                <value>游泳</value>
                <value>跑步</value>
                <value>骑车</value>
            </array>
        </property>
        <property name="teacherMap" ref="teacherMap"> </property>
    </bean>

</beans>

4.9.2、测试

    @Test
    public void testDIUtil(){
        ApplicationContext applicationContext = new ClassPathXmlApplicationContext("spring-ioc.xml");
        Student student = applicationContext.getBean("studentNine", Student.class);
        System.out.println(student);
    }

4.10、p命名空间(了解)

4.10.1、配置bean

注意：p命名空间的依赖注入，本质上是属性方式（setter方法）的依赖注入

<?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">

    <!--map集合类型的bean-->
    <util:map id="teacherMap">
        <entry key="10010" value-ref="teacherOne"></entry>
        <entry key="10086" value-ref="teacherTwo"></entry>
    </util:map>

    <bean id="studentTen" class="org.rain.spring.pojo.Student"
    p:id="1001" p:name="张三" p:teacherMap-ref="teacherMap"></bean>

</beans>

4.10.2、测试

    @Test
    public void testDIP(){
        ApplicationContext applicationContext = new ClassPathXmlApplicationContext("spring-ioc.xml");
        Student student = applicationContext.getBean("studentTen", Student.class);
        System.out.println(student);
    }

4.11、引入外部属性文件

4.11.1、引入数据库相关依赖

        <!-- MySQL驱动 -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.49</version>
        </dependency>
        <!-- 数据源 -->
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>druid</artifactId>
            <version>1.0.31</version>
        </dependency>

4.11.2、创建外部属性文件

jdbc.driver=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/ssm?characterEncoding=utf-8
jdbc.username=root
jdbc.password=root

4.11.3、配置bean

注意：使用context:property-placeholder标签必须引入相应的XML命名空间

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

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

    <bean id="datasource" class="com.alibaba.druid.pool.DruidDataSource">
        <!--通过${key}的方式访问外部属性文件的value-->
        <property name="driverClassName" value="${jdbc.driver}"></property>
        <property name="url" value="${jdbc.url}"></property>
        <property name="username" value="${jdbc.username}"></property>
        <property name="password" value="${jdbc.password}"></property>
    </bean>

</beans>

4.11.4、测试

    @Test
    public void testDIOuterFile() throws SQLException {
        ApplicationContext applicationContext = new ClassPathXmlApplicationContext("spring-datasource");
        DruidDataSource datasource = applicationContext.getBean("datasource", DruidDataSource.class);
        System.out.println(datasource.getConnection());
    }

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