准备

准备如下 POJO：

// com.zze.bean.Department
package com.zze.bean;

public class Department {
    public Department() {
    }

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

    private String name;

    public String getName() {
        return name;
    }

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

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

// com.zze.bean.User
package com.zze.bean;

public class User {

    public User() {
    }

    public User(String name, Integer age, Department department) {
        this.name = name;
        this.age = age;
        this.department = department;
    }

    private String name;
    private Integer age;
    private Department department;

    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 Department getDepartment() {
        return department;
    }

    public void setDepartment(Department department) {
        this.department = department;
    }

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

几种注入方式

构造方法注入

<bean name="department" class="com.zze.bean.Department">
    <constructor-arg name="name" value="信息部"/>
</bean>

<bean name="user" class="com.zze.bean.User">
    <constructor-arg name="name" value="李四"/>
    <constructor-arg name="age" value="30"/>
    <constructor-arg name="department" ref="department"/>
</bean>

ApplicationContext applicationContext = new ClassPathXmlApplicationContext("applicationContext.xml");
Object user = applicationContext.getBean("user");

System.out.println(user);
/*
User{name='李四', age=30, department=Department{name='信息部'}}
 */

setter 注入

<bean name="department" class="com.zze.bean.Department">
    <property name="name" value="信息部"/>
</bean>

<bean name="user" class="com.zze.bean.User">
    <property name="name" value="张三"/>
    <property name="age" value="12"/>
    <property name="department" ref="department"/>
</bean>

ApplicationContext applicationContext = new ClassPathXmlApplicationContext("applicationContext.xml");
Object user = applicationContext.getBean("user");
System.out.println(user);
/*
User{name='张三', age=12, department=Department{name='信息部'}}
 */

p 名称空间注入

<!--
    在 Spring 2.5 之后支持。
    需在 beans 标签中添加属性 xmlns:p="http://www.springframework.org/schema/p" 来引入 p 名称空间
-->
<bean name="department" class="com.zze.bean.Department" p:name="信息部"/>

<bean name="user" class="com.zze.bean.User" p:name="张三" p:age="21" p:department-ref="department"/>

ApplicationContext applicationContext = new ClassPathXmlApplicationContext("applicationContext.xml");
Object user = applicationContext.getBean("user");
System.out.println(user);
/*
User{name='张三', age=21, department=Department{name='信息部'}}
 */

SpEL 注入

<!--
    在 Spring 3.0 之后支持。
-->
<bean name="department" class="com.zze.bean.Department">
    <property name="name" value="#{'推广部'}"/>
</bean>

<bean name="user" class="com.zze.bean.User">
    <property name="name" value="#{'李四'}"/>
    <!--在表达式中可以有计算操作，并且可以直接调用对象属性及方法-->
    <property name="age" value="#{10+22}"/>
    <property name="department" ref="department"/>
</bean>

ApplicationContext applicationContext = new ClassPathXmlApplicationContext("applicationContext.xml");
Object user = applicationContext.getBean("user");
System.out.println(user);
/*
User{name='李四', age=32, department=Department{name='推广部'}}
 */

其它

注入Array

// com.zze.bean.Customer
package com.zze.bean;

import java.util.Arrays;

public class Customer {
    private String name;
    private String[] hobbies;

    public String getName() {
        return name;
    }

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

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

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

    @Override
    public String toString() {
        return "Customer{" +
                "name='" + name + '\'' +
                ", hobbies=" + Arrays.toString(hobbies) +
                '}';
    }
}

<!--
    List 和 Set 的注入方式与 Array 一致
-->
<bean name="customer" class="com.zze.bean.Customer">
    <property name="name" value="二狗"/>
    <property name="hobbies">
        <list>
            <value>吃饭</value>
            <value>睡觉</value>
            <value>打豆豆</value>
        </list>
    </property>
</bean>

ApplicationContext applicationContext = new ClassPathXmlApplicationContext("applicationContext.xml");
Object user = applicationContext.getBean("customer");
System.out.println(user);
/*
Customer{name='二狗', hobbies=[吃饭, 睡觉, 打豆豆]}
*/

注入 Map

// com.zze.bean.TestBean
package com.zze.bean;

import java.util.Map;

public class TestBean {
    private Map<String, Object> map;

    public Map<String, Object> getMap() {
        return map;
    }

    public void setMap(Map<String, Object> map) {
        this.map = map;
    }

    @Override
    public String toString() {
        return "TestBean{" +
                "map=" + map +
                '}';
    }
}

<bean id="testBean" class="com.zze.bean.TestBean">
    <property name="map">
        <map>
            <entry key="1" value="a"/>
            <entry key="2" value="b"/>
            <entry key="3" value="c"/>
        </map>
    </property>
</bean>

ApplicationContext applicationContext = new ClassPathXmlApplicationContext("applicationContext.xml");
Object testBean = applicationContext.getBean("testBean");
System.out.println(testBean);
/*
TestBean{map={1=a, 2=b, 3=c}}
 */