Spring Bean 的属性注入

Spring Bean 的属性注入常见有以下几种：

• 构造器注入
• Setter注入
• 名称空间注入
• SpEL注入

常见注意事项：

• value是普通值，ref是引用注入，引用其他bean
• 构造器注入时，index表示编号（从0开始），name表示名称，type表示类型
• p名称空间注入时，要设置命名空间：xmlns:p=“http://www.springframework.org/schema/p”

SpEL语法

语法	用法
#{‘String’}	使用字符串
#{beanId}	使用另一个bean
#{beanId.content.toUpperCase()}	使用指定名属性，并使用放法
#{T(java.lang.Math).PI}	使用静态字段或方法

下面通过简单示例分别测试

文件目录

di
- src
- - main
- - - java
- - - - com.zhangxin9727
- - - - - Cat.java
- - - - - Person.java
- - - resources
- - - - bean.xml
- - test
- - - java
- - - - MyTest.java
- pom.xml

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <maven.compiler.source>11</maven.compiler.source>
        <maven.compiler.target>11</maven.compiler.target>
    </properties>

    <groupId>com.zhangxin9727</groupId>
    <artifactId>di</artifactId>
    <version>1.0-SNAPSHOT</version>

    <dependencies>
        <dependency>
            <groupId>org.junit.jupiter</groupId>
            <artifactId>junit-jupiter-api</artifactId>
            <version>5.4.0</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-context</artifactId>
            <version>5.1.4.RELEASE</version>
        </dependency>
    </dependencies>

</project>

Person.java

package com.zhangxin9727;

public class Person {
    private String name;
    private int age;
    private Cat cat;

    public Person() {
    }

    public Person(String name, int age, Cat cat) {
        this.name = name;
        this.age = age;
        this.cat = cat;
    }

    public void setName(String name) {
        this.name = name;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public void setCat(Cat cat) {
        this.cat = cat;
    }

    @Override
    public String toString() {
        return "Person{" + "name='" + name + '\'' + ", age=" + age + ", cat=" + cat + '}';
    }
}

Cat.java

package com.zhangxin9727;

public class Cat {
    private String name;

    public Cat() {
    }

    public Cat(String name) {
        this.name = name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return "Cat{" + "name='" + name + '\'' + '}';
    }
}

bean.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:p="http://www.springframework.org/schema/p"
       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">

    <!--构造器注入-->
    <bean id="cat1" class="com.zhangxin9727.Cat">
        <constructor-arg name="name" value="kitty"/>
    </bean>
    <bean id="person1" class="com.zhangxin9727.Person">
        <constructor-arg name="name" value="Alice"/>
        <constructor-arg index="1" value="16"/>
        <constructor-arg type="com.zhangxin9727.Cat" ref="cat1"/>
    </bean>

    <!--Setter注入-->
    <bean id="cat2" class="com.zhangxin9727.Cat">
        <property name="name" value="Kitty"/>
    </bean>
    <bean id="person2" class="com.zhangxin9727.Person">
        <property name="name" value="Alice"/>
        <property name="age" value="16"/>
        <property name="cat" ref="cat2"/>
    </bean>

    <!--p名称空间注入-->
    <bean id="cat3" class="com.zhangxin9727.Cat" p:name="Kitty"/>
    <bean id="person3" class="com.zhangxin9727.Person" p:name="Alice" p:age="16" p:cat-ref="cat3"/>

    <!--SpEL注入-->
    <bean id="cat4" class="com.zhangxin9727.Cat">
        <property name="name" value="#{'Kitty'}"/>
    </bean>
    <bean id="person4" class="com.zhangxin9727.Person">
        <property name="name" value="#{'Alice'}"/>
        <property name="age" value="#{16}"/>
        <property name="cat" value="#{cat4}"/>
    </bean>

</beans>

MyTest.java

import com.zhangxin9727.Person;
import org.junit.jupiter.api.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class MyTest {
    @Test
    public void test1() {
        ApplicationContext applicationContext = new ClassPathXmlApplicationContext("bean.xml");
        Person person = (Person) applicationContext.getBean("person1");
        System.out.println(person);
    }

    @Test
    public void test2() {
        ApplicationContext applicationContext = new ClassPathXmlApplicationContext("bean.xml");
        Person person = (Person) applicationContext.getBean("person2");
        System.out.println(person);
    }

    @Test
    public void test3() {
        ApplicationContext applicationContext = new ClassPathXmlApplicationContext("bean.xml");
        Person person = (Person) applicationContext.getBean("person3");
        System.out.println(person);
    }

    @Test
    public void test4() {
        ApplicationContext applicationContext = new ClassPathXmlApplicationContext("bean.xml");
        Person person = (Person) applicationContext.getBean("person4");
        System.out.println(person);
    }
}