2-2、依赖注入以及特殊属性的赋值

2.4、依赖注入的三种方式

我们在Spring配置文件中引入的bean初始值是空的，依赖注入就是给他们赋值。这里主要介绍三种常用的方式。

1、setter注入

<bean id="student" class="com.lu.Spring.pojo.Student">
    <property name="id" value="1001">property>
    <property name="name" value="李白">property>
    <property name="age" value="25">property>
    <property name="gender" value="男">property>
bean>
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利用properties标签给对应的属性赋值（本质是调用set()方法）。

2、构造器注入

构造器注入要求在对应的实体类中编写有参构造，其本质是调用有参构造来进行初始化。

<bean id="student" class="com.lu.Spring.pojo.Student">
    <constructor-arg value="1001">constructor-arg>
    <constructor-arg value="李白">constructor-arg>
    <constructor-arg value="25">constructor-arg>
    <constructor-arg value="男">constructor-arg>
bean>
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默认是按照构造器参数的顺序进行赋值，也可以用name属性指定赋值。

<bean id="student" class="com.lu.Spring.pojo.Student">
    <constructor-arg value="1001" name="age">constructor-arg>
    <constructor-arg value="李白">constructor-arg>
    <constructor-arg value="25" name="id">constructor-arg>
    <constructor-arg value="男">constructor-arg>
bean>
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3、依赖注入P命名空间

p命名空间是根据属性来注入依赖的，相当于将property标签换成p:来进行注入。

<bean id="student_p" class="com.lu.Spring.pojo.Student"
      p:id="1001"
      p:name="苏轼"
      p:age="20"
      p:gender="男"
>bean>
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2.5、依赖注入的特殊值处理

1、赋值null

当我们想要给属性赋值为null时，不能直接value="null",这样是给属性赋值字符串"null"。

<bean id="student" class="com.lu.Spring.pojo.Student">
    <property name="id" value="1001">property>
    <property name="name" value="null">property>
    <property name="age" value="20">property>
    <property name="gender" value="男">property>
bean>
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要利用标签来进行赋值。这样的话才能赋空值。

<bean id="student" class="com.lu.Spring.pojo.Student">
    <property name="id" value="1001">property>
    <property name="name" >
        <null>null>
    property>
    <property name="age" value="20">property>
    <property name="gender" value="男">property>
bean>
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输出name.toString()，会报空指针异常，代表name属性值为空。

@Test
public void test(){
    //1.获取ApplicationContext
    ApplicationContext applicationContext = new ClassPathXmlApplicationContext("applicationContext.xml");
    //2.获取指定类对象
    Student student = (Student) applicationContext.getBean("student");
    applicationContext.getBean(Student.class);

    System.out.println(student.getName().toString());
}
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2、特殊字符的赋值

当我们给属性赋值内容中含有特殊字符时，比如给name赋值为<李白>,含有尖括号是特殊字符，有两种解决办法。

①、用xml实体来代替特殊字符。

< 的xml实体是<;> 的xml实体是>;

<bean id="student" class="com.lu.Spring.pojo.Student">
    <property name="id" value="1001">property>
    <property name="name" value="<李白>">property>
    <property name="age" value="20">property>
    <property name="gender" value="男">property>
bean>
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②、用CDATA节。

CDATA节内的特殊字符都会被当作普通字符。

CDATA节只能写在value标签中，而不能写在value属性中。

<bean id="student" class="com.lu.Spring.pojo.Student">
    <property name="id" value="1001">property>
    <property name="name" >
        <value> ]]>value>
    property>
    <property name="age" value="20">property>
    <property name="gender" value="男">property>
bean>
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2.6、为数组类型的属性赋值

<bean id="student" class="com.lu.Spring.pojo.Student">
    <property name="id" value="1001">property>
    <property name="name" value="李白">property>
    <property name="age" value="25">property>
    <property name="gender" value="男">property>
    <property name="hobbys">
        <array>
            <value>舞剑value>
            <value>吟诗value>
            <value>喝酒value>
        array>
    property>
bean>
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2.7、属性为类时的赋值

当实体类中的属性含有内部类时，对该属性的赋值有三种方法：

1、引用外部bean

<bean id="student" class="com.lu.Spring.pojo.Student">
    <property name="id" value="1001">property>
    <property name="name" value="李白">property>
    <property name="age" value="20">property>
    <property name="gender" value="男">property>
    <property name="teacher" ref="teacher">property>
bean>

<bean id="teacher" class="com.lu.Spring.pojo.Teacher">
    <property name="name" value="裴旻">property>
    <property name="age" value="40">property>
    <property name="email" value="232156@qq.com">property>
bean>
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利用ref属性，引用外部bean。

2、内部bean

<bean id="student" class="com.lu.Spring.pojo.Student">
    <property name="id" value="1001">property>
    <property name="name" value="李白">property>
    <property name="age" value="20">property>
    <property name="gender" value="男">property>
    <property name="teacher" >
        <bean id="teacher" class="com.lu.Spring.pojo.Teacher">
            <property name="name" value="裴旻">property>
            <property name="age" value="40">property>
            <property name="email" value="232156@qq.com">property>
        bean>
    property>
bean>
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3、级联赋值

<bean id="student" class="com.lu.Spring.pojo.Student">
    <property name="id" value="1001">property>
    <property name="name" value="李白">property>
    <property name="age" value="20">property>
    <property name="gender" value="男">property>
    
    <property name="teacher" ref="teacher">property>
    <property name="teacher.name" value="裴旻">property>
    <property name="teacher.age" value="40">property>
    <property name="teacher.email" value="232156@qq.com">property>
bean>
<bean id="teacher" class="com.lu.Spring.pojo.Teacher">bean>
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2.8、为集合类型的属性赋值

当属性为集合时，对集合的赋值分两种情况。

1、属性为list集合的赋值

①、内部list赋值

<bean id="teacher" class="com.lu.Spring.pojo.Teacher">
    <property name="name" value="孔子">property>
    <property name="age" value="50">property>
    <property name="email" value="001@qq.com">property>
    <property name="studentList" >
        <list>
            <ref bean="student01">ref>
            <ref bean="student02">ref>
            <ref bean="student03">ref>
        list>
    property>
bean>

<bean id="student01" class="com.lu.Spring.pojo.Student">
    <property name="id" value="3001">property>
    <property name="name" value="颜回">property>
    <property name="age" value="30">property>
    <property name="gender" value="男">property>
bean>
<bean id="student02" class="com.lu.Spring.pojo.Student">
    <property name="id" value="3002">property>
    <property name="name" value="闵损">property>
    <property name="age" value="28">property>
    <property name="gender" value="男">property>
bean>
<bean id="student03" class="com.lu.Spring.pojo.Student">
    <property name="id" value="3003">property>
    <property name="name" value="仲由">property>
    <property name="age" value="25">property>
    <property name="gender" value="男">property>
bean>
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②、引用外部list赋值

<bean id="teacher" class="com.lu.Spring.pojo.Teacher">
    <property name="name" value="孔子">property>
    <property name="age" value="50">property>
    <property name="email" value="001@qq.com">property>
    <property name="studentList" ref="students">property>
bean>

<util:list id="students" >
    <ref bean="student01">ref>
    <ref bean="student02">ref>
    <ref bean="student03">ref>
util:list>

<bean id="student01" class="com.lu.Spring.pojo.Student">
    <property name="id" value="3001">property>
    <property name="name" value="颜回">property>
    <property name="age" value="30">property>
    <property name="gender" value="男">property>
bean>
<bean id="student02" class="com.lu.Spring.pojo.Student">
    <property name="id" value="3002">property>
    <property name="name" value="闵损">property>
    <property name="age" value="28">property>
    <property name="gender" value="男">property>
bean>
<bean id="student03" class="com.lu.Spring.pojo.Student">
    <property name="id" value="3003">property>
    <property name="name" value="仲由">property>
    <property name="age" value="25">property>
    <property name="gender" value="男">property>
bean>
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2、属性为map集合的赋值

<bean id="student" class="com.lu.Spring.pojo.Student">
    <property name="id" value="1001">property>
    <property name="name" value="李白">property>
    <property name="age" value="25">property>
    <property name="gender" value="男">property>
    <property name="subject" ref="map">property>
bean>

<util:map id="map">
    <entry key="术算" value-ref="teacher1">entry>
    <entry key="剑术" value-ref="teacher2">entry>
util:map>

<bean id="teacher1" class="com.lu.Spring.pojo.Teacher">
    <property name="name" value="赵蕤">property>
    <property name="age" value="40">property>
    <property name="email" value="232156@qq.com">property>
bean>
<bean id="teacher2" class="com.lu.Spring.pojo.Teacher">
    <property name="name" value="裴旻">property>
    <property name="age" value="40">property>
    <property name="email" value="232156@qq.com">property>
bean>
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2.9、Spring管理数据源和引入外部属性文件

引入jdbc.properties：

1、Resource下面新建jdbc.properties

2、Spring配置文件中引入

<context:property-placeholder location="jdbc.properties">context:property-placeholder>
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管理数据源

1、引入Maven依赖

<dependency>
    <groupId>mysqlgroupId>
    <artifactId>mysql-connector-javaartifactId>
    <version>8.0.29version>
dependency>
<dependency>
    <groupId>com.alibabagroupId>
    <artifactId>druidartifactId>
    <version>1.2.11version>
dependency>
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2、配置Spring文件

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

<bean id="dataSource" class="com.alibaba.druid.pool.DruidDataSource">
    <property name="driver" 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>
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3、获取连接

    @Test
    public void test() throws SQLException {
        //1.获取ApplicationContext
        ApplicationContext applicationContext = new ClassPathXmlApplicationContext("a.xml");
        //2.获取指定类对象
        DruidDataSource dataSource = applicationContext.getBean(DruidDataSource.class);
        //3.获取链接
        Connection connection = dataSource.getConnection();

        System.out.println(connection);
    }
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