Spring框架依赖注入方法示例

在阅读这篇文章之前，大家可以先参阅《理解Spring中的依赖注入和控制反转》一文，了解下依赖注入和控制反转的相关内容。

三种依赖注入的方式

属性注入，通过setter方法注入bean的属性值或依赖的对象 构造注入 工厂方法注入（很少使用）
例子

这里我们使用了spring-4.3.2，maven配置文件

<dependency>
 <groupid>org.springframework</groupid>
 spring-core</artifactid>
 <version>${org.springframework-version}</version>
 <exclusions>
  <exclusion>
   <groupid>commons-logging</groupid>
   commons-logging</artifactid>
  </exclusion>
 </exclusions>
</dependency>
<dependency>
 <groupid>org.springframework</groupid>
 spring-beans</artifactid>
 <version>${org.springframework-version}</version>
</dependency>
<dependency>
 <groupid>org.springframework</groupid>
 spring-aop</artifactid>
 <version>${org.springframework-version}</version>
</dependency>
<dependency>
 <groupid>org.springframework</groupid>
 spring-context</artifactid>
 <version>${org.springframework-version}</version>
</dependency>
<dependency>
 <groupid>commons-logging</groupid>
 commons-logging</artifactid>
 <version>1.2</version>
</dependency>
<!-- Junit -->
<dependency>
 <groupid>junit</groupid>
 junit</artifactid>
 <version>3.8.1</version>
 <scope>test</scope>
</dependency>

applicationContext.xml配置文件

<!--?xml version="1.0" encoding="UTF-8"?-->
<beans xmlns="https://www.springframework.org/schema/beans" xmlns:p="https://www.springframework.org/schema/p" xmlns:util="https://www.springframework.org/schema/util" xmlns:xsi="https://www.w3.org/2001/XMLSchema-instance" xsi:schemalocation="https://www.springframework.org/schema/beans https://www.springframework.org/schema/beans/spring-beans.xsd
  https://www.springframework.org/schema/util https://www.springframework.org/schema/util/spring-util.xsd">

 <!--
  配置bean
  id：标识容器中bean对象
  class：bean的全类名，通过反射的方式在IOC容器中创建Bean，所以要求Bean类必须有无参构造器
  -->
 <bean class="com.spring.test.HelloWorld" id="helloWorld">
  <property name="name" value="crystal"></property>
 </bean>

 <!-- 通过构造方法配置bean,可以指定参数的位置和类型，以区分重载的构造函数 -->
 <bean class="com.spring.test.Car" id="car">
  <constructor-arg index="0" value="BENCHI"></constructor-arg>
  <constructor-arg index="1" type="double" value="200000.0"></constructor-arg>
 </bean>
 <bean class="com.spring.test.Car" id="car1">
  <!-- 如果字面值包含特殊字符，使用<![CDATA[]]>包裹起来
   属性值可以使用value子节点来配置
   -->
  <constructor-arg type="java.lang.String">
   <value><!--[CDATA[<shanghai-->]]></value>
  </constructor-arg>
  <constructor-arg index="1" type="int" value="200"></constructor-arg>
 </bean>

 <bean class="com.spring.test.Person" id="person">
  <property name="name" value="Crystal"></property>
  <property name="age" value="20"></property>
  <!-- 可以使用ref建立引用之间的关系 -->
  <!--
  <property name="car" ref="car"></property>
   -->
  <!--
   <property name="car">
    <ref bean="car2"/>
   </property>
   -->
   <!--
   <property name="car">
   <bean class="com.spring.test.Car">
    <constructor-arg value="changanFute"></constructor-arg>
    <constructor-arg value="3000000"></constructor-arg>
    <constructor-arg value="240"></constructor-arg>
   </bean>
   </property>
   -->
   <!-- 测试赋值null -->
   <!-- <property name="car"><null/></property> -->
   <property name="car" ref="car1"></property>
   <!-- 为级联属性赋值，注意：属性需要先初始化后才能为级联属性赋值，和structs2不同 -->
   <property name="car.price" value="400000"></property>
 </bean>

 <!-- 测试配置集合属性 -->
 <bean class="com.spring.test.collections.Person" id="person3">
  <property name="name" value="barry"></property>
  <property name="age" value="21"></property>
  <property name="cars">
   <list>
    <ref bean="car">
    <ref bean="car1">
    <bean class="com.spring.test.Car">
     <constructor-arg value="changanFute"></constructor-arg>
     <constructor-arg value="3000000"></constructor-arg>
     <constructor-arg value="240"></constructor-arg>
    </bean>
   </ref></ref></list>
  </property>
 </bean>

 <!-- 配置Map的属性值 -->
 <bean class="com.spring.test.collections.NewPerson" id="newPerson">
  <property name="name" value="lina"></property>
  <property name="age" value="22"></property>
  <property name="cars">
   <!-- 使用map节点及map的entry子节点配置Map类型的成员变量 --><map>
    <entry key="AA" value-ref="car"></entry>
    <entry key="BB" value-ref="car1"></entry></map>
  </property>
 </bean>

 <!-- 配置Properties属性值 -->
 <bean class="com.spring.test.collections.DataSource" id="dataSource">
  <property name="properties">
   <!-- 使用props和prop子节点来为Properties属性赋值 -->
   <props>
    <prop key="user">root</prop>
    <prop key="password">1234</prop>
    <prop key="jdbcUrl">jdbc:mysql://test</prop>
    <prop key="jdbcDriver">com.mysql.jdbc.Driver</prop>
   </props>
  </property>
 </bean>

 <!-- 配置单例的集合bean，以供多个bean进行引用，需要导入util命名空间 -->
 <util:list id="cars">
  <ref bean="car">
  <ref bean="car1">
 </ref></ref></util:list>

 <bean class="com.spring.test.collections.Person" id="person4">
  <property name="name" value="Jackie"></property>
  <property name="age" value="30"></property>
  <property name="cars" ref="cars"></property>
 </bean>

 <!-- 通过p命名空间为bean的属性赋值，需要先导入p命名空间，相对于传统配置方式更为简洁 -->
 <bean class="com.spring.test.collections.Person" id="person5" p:age="32" p:cars-ref="cars" p:name="Queue"></bean>
</beans>

1. 下面是简单的属性注入、构造注入的测试类

Car.java

package com.spring.test;
public class Car {
	private String name;
	private int maxSpeed;
	private double price;
	public Car() {
	}
	public Car(String name, double price) {
		this.name = name;
		this.price = price;
	}
	public Car(String name, int maxSpeed) {
		this.name = name;
		this.maxSpeed = maxSpeed;
	}
	public Car(String name, double price, int maxSpeed) {
		this.name = name;
		this.price = price;
		this.maxSpeed = maxSpeed;
	}
	public void setPrice(double price) {
		this.price = price;
	}
	@Override
	 public String toString() {
		return "Car [name:" + name + ", price:" + price + ", maxSpeed:" + maxSpeed + "]";
	}
}

HelloWorld.java

package com.spring.test;
public class HelloWorld {
	private String name;
	public HelloWorld() {
		System.out.println("HelloWorld constructor...");
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		System.out.println("setName:" + name);
		this.name = name;
	}
	@Override
	 public String toString() {
		return "hello," + name;
	}
}

Person.java

package com.spring.test;
public class Person {
	private String name;
	private int age;
	private Car car;
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public int getAge() {
		return age;
	}
	public void setAge(int age) {
		this.age = age;
	}
	public Car getCar() {
		return car;
	}
	public void setCar(Car car) {
		this.car = car;
	}
	@Override
	 public String toString() {
		return "Person: [name=" + name + ", age=" + age + ", car=" + car + "]";
	}
}

Main.java

package com.spring.test;
import org.junit.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class Main {
	public static void main(String[] args) {
		HelloWorld hello = new HelloWorld();
		hello.setName("barry");
		System.out.println("print:"+ hello + "\n");
		// 装入 Spring 配置文件
		/**
   * 装入 Spring 配置文件
   * ApplicationContext是IOC容器，它有两个主要实现类（ClassPathXmlApplicationContext和FileSystemXmlApplicationContext）
   * ApplicationContext在初始化上下文时就实例化所有单例的Bean
   */
		ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
		//HelloWorld hello1 = (HelloWorld) context.getBean("helloWorld"); // 通过id获取bean对象
		HelloWorld hello1 = context.getBean(HelloWorld.class);
		// 通过类型获取bean对象（要求在IOC容器里该类型的对象只能有一个）
		System.out.println(hello1);
	}
	@Test
	 public void testContructor() {
		ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
		Car car = (Car) context.getBean("car");
		// 通过类型获取bean对象（要求在IOC容器里该类型的对象只能有一个）
		Car car1 = (Car) context.getBean("car1");
		System.out.println(car);
		System.out.println(car1);
		Person person = (Person) context.getBean("person");
		System.out.println(person);
	}
}

2. 下面是集合的测试类
NewPerson.java

package com.spring.test.collections;
import java.util.Map;
import com.spring.test.Car;
public class NewPerson {
	private String name;
	private int age;
	private Map<string, car=""> cars;
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public int getAge() {
		return age;
	}
	public void setAge(int age) {
		this.age = age;
	}
	public Map<string, car=""> getCars() {
		return cars;
	}
	public void setCars(Map<string, car=""> cars) {
		this.cars = cars;
	}
	@Override
	 public String toString() {
		return "Person: [name=" + name + ", age=" + age + ", cars=" + cars + "]";
	}
}

Person.java

package com.spring.test.collections;
import java.util.List;
import com.spring.test.Car;
public class Person {
	private String name;
	private int age;
	private List<car> cars;
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public int getAge() {
		return age;
	}
	public void setAge(int age) {
		this.age = age;
	}
	public List<car> getCars() {
		return cars;
	}
	public void setCars(List<car> cars) {
		this.cars = cars;
	}
	@Override
	 public String toString() {
		return "Person: [name=" + name + ", age=" + age + ", cars=" + cars + "]";
	}
}

DataSource.java

package com.spring.test.collections;
import java.util.Properties;
public class DataSource {
	private Properties properties;
	public Properties getProperties() {
		return properties;
	}
	public void setProperties(Properties properties) {
		this.properties = properties;
	}
	@Override
	 public String toString() {
		return "DataSource: [properties:" + properties + "]";
	}
}

Main.java

package com.spring.test.collections;
import org.junit.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class Main {
	@Test
	 public void testCollections() {
		ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
		Person person = (Person) context.getBean("person3");
		System.out.println(person);
		NewPerson newPerson = (NewPerson) context.getBean("newPerson");
		System.out.println(newPerson);
		DataSource dataSource = (DataSource) context.getBean("dataSource");
		System.out.println(dataSource);
		Person person4 = (Person) context.getBean("person4");
		System.out.println(person4);
		Person person5 = (Person) context.getBean("person5");
		System.out.println(person5);
	}
}

总结

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