控制反转 Inversion of Control

Spring 控制反转容器的使用

通过构造器创建一个 bean 实例

<!-- spring-config.xml -->
<?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">

    <bean name="product" class="app15a.bean.Product" />  <!-- 注意应采用 id 或者 name 属性标识一个 bean -->
    
</beans>

该 bean 的定义告诉 Spring 通过默认的无参构造器来初始化 Product 类，如果不存在无参构造器，则 Spring 将抛出一个异常。

为了让 Spring 创建一个 Product 实例，应将 bean 定义的 name 值（或者 id 值）和 Product 类型作为参数传递给 ApplicationContext 的 getBean 方法：

ApplicationContext context = new ClassPathXmlApplicationContext(new String[] {"spring-config.xml"});  // 导入配置文件 
Product product1 = context.getBean("product", Product.class);  // 让 Spring 创建一个 Product 实例  
product1.setName("Excellent snake oil");  // 给 product 的 name 属性赋值 
System.out.println("product1: " + product1.getName());  // 获取 product 的 name 属性

通过工厂方法创建一个 bean 实例

<!-- spring-config.xml -->
<?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">

    <bean id="calendar" class="java.util.Calendar" factory-method="getInstance" />  
</beans>

ApplicationContext context = new ClassPathXmlApplicationContext(new String[] {"spring-config.xml"});  // 导入配置文件 
Product product1 = context.getBean("calendar", Calendar.class);  // 让 Spring 创建一个 Calendar 实例  

Destroy Method 的使用

 可以在 bean 定义中配置 destroy-method 属性，用来指定在销毁前要被执行的方法。

在该例子中，配置 Spring 通过 java.util.concurrent.Executors 的静态方法 newCachedThreadPool 创建一个 java.util.concurrent.ExecutorService 实例，并指定了 destroy-method 属性值为 shutdown 方法，这样，Spring 会在销毁 ExecutorService 实例前调用其 shutdown 方法。

<!-- spring-config.xml -->
<?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">

    <bean id="executorService" class="java.util.concurrent.Executors" factory-method="newCachedThreadPool" destroy-method="shutdown" />  
</beans>

向构造器传递参数

package app15a.bean;

import java.io.Serializable;

public class Product implements Serializable {
    private static final long serialVersionUID = 748392348L;
    
    private String name;
    private String description;
    private float price;
    
    public Product() {  // 无参构造器
    }
    public Product(String name, String description, float price) {  // 有参构造器
        this.name = name;
        this.description = description;
        this.price = price;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getDescription() {
        return description;
    }
    public void setDescription(String description) {
        this.description = description;
    }
    public float getPrice() {
        return price;
    }
    public void setPrice(float price) {
        this.price = price;
    }
}

配置文件 spring-config.xml

<!-- spring-config.xml -->
<?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">

    <bean name="featuredProduct" class="app15a.bean.Product" >
        <constructor-arg name="name" value="Ultimate Olive Oil" />  <!-- 通过参数名向构造函数传递参数 -->
        <constructor-arg name="description" value="The purest olive on the market" />
        <constructor-arg name="price" value="9.95" />
    </bean>
    
</beans>

这样，在创建 Product 实例时，Spring 会调用以下构造器

public Product(String name, String description, float price) {  // 有参构造器
    this.name = name;
    this.description = description;
    this.price = price;
}

setter方式依赖注入

package app15a.bean;

public class Address {
    private String line1;
    private String line2;
    private String city;
    private String state;
    private String zipCode;
    private String country;
    
    public Address(String line1, String line2, String city, String state, String zipCode, String country) {
        this.line1 = line1;
        this.line2 = line2;
        this.city = city;
        this.state = state;
        this.zipCode = zipCode;
        this.country = country;
    }

    public String getLine1() {
        return line1;
    }

    public void setLine1(String line1) {
        this.line1 = line1;
    }

    public String getLine2() {
        return line2;
    }

    public void setLine2(String line2) {
        this.line2 = line2;
    }

    public String getCity() {
        return city;
    }

    public void setCity(String city) {
        this.city = city;
    }

    public String getState() {
        return state;
    }

    public void setState(String state) {
        this.state = state;
    }

    public String getZipCode() {
        return zipCode;
    }

    public void setZipCode(String zipCode) {
        this.zipCode = zipCode;
    }

    public String getCountry() {
        return country;
    }

    public void setCountry(String country) {
        this.country = country;
    }
    @Override
    public String toString() {
        return line1 + "
" + 
               line2 + "
" +
               city + "
" +
               state + " " + zipCode + "
" +
               country;
    }
}
//////////////////////////////
package app15a.bean;

public class Employee {
    private String firstName;
    private String lastName;
    private Address homeAddress;
    
    public Employee() {
    }
    public Employee(String firstName, String lastName, Address homeAddress) {
        this.firstName = firstName;
        this.lastName = lastName;
        this.homeAddress = homeAddress;
    }
    public String getFirstName() {
        return firstName;
    }
    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }
    public String getLastName() {
        return lastName;
    }
    public void setLastName(String lastName) {
        this.lastName = lastName;
    }
    public Address getHomeAddress() {
        return homeAddress;
    }
    public void setHomeAddress(Address homeAddress) {
        this.homeAddress = homeAddress;
    }
    @Override
    public String toString() {
        return firstName + " " + lastName + "
" + homeAddress;
    }
}

配置文件 spring-config.xml

<!-- spring-config.xml -->
<?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">

    <bean name="simpleAddress" class="app15a.bean.Address" >
        <!-- 通过构造方法传递参数 -->
        <constructor-arg name="line1" value="151 Corner Street" />
        <constructor-arg name="line2" value="" />
        <constructor-arg name="city" value="Albany" />
        <constructor-arg name="state" value="NY" />
        <constructor-arg name="zipCode" value="99999" />
        <constructor-arg name="country" value="US" />
    </bean>
    
    <bean name="employ2" class="app15a.bean.Employee">
        <!-- setter方式依赖注入 -->
        <property name="homeAddress" ref="simpleAddress" />
        <property name="firstName" value="Junior" />
        <property name="lastName" value="Moore" />
    </bean>
    
</beans>

simpleAddress 对象是 Address 类的一个实例，其通过构造器方式实例化；employ1 对象则通过配置 property 元素来调用 setter 方法来设置值。

homeAddress 属性配置的是 simpleAddress 对象的引用。

构造器方式依赖注入

<!-- spring-config.xml -->
<?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">

    <bean name="employ2" class="app15a.bean.Employee">
        <!-- 构造器方式依赖注入 -->
        <constructor-arg name="firstName" ref="Senior" />
        <constructor-arg name="lastName" value="Moore" />
        <constructor-arg name="homeAddress" value="simpleAddress" />
    </bean>
    
    <bean name="simpleAddress" class="app15a.bean.Address" >
        <!-- 通过构造方法传递参数 -->
        <constructor-arg name="line1" value="151 Corner Street" />
        <constructor-arg name="line2" value="" />
        <constructor-arg name="city" value="Albany" />
        <constructor-arg name="state" value="NY" />
        <constructor-arg name="zipCode" value="99999" />
        <constructor-arg name="country" value="US" />
    </bean>
    
</beans>