Spring控制反转容器的使用

主要介绍Spring如何管理bean和依赖关系。

通过构造器创建一个bean的实例

之前的方法中，可以通过调用ApolicationContext的getBean方法可以获取到一个bean的实例。下面的配置文件中定义了一个名为product的bean。

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<span style="font-size:14px;"><?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:tx="http://www.springframework.org/schema/tx"  xmlns:context="http://www.springframework.org/schema/context"  xmlns:mvc="http://www.springframework.org/schema/mvc"  xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-3.2.xsd
http://www.springframework.org/schema/tx
http://www.springframework.org/schema/tx/spring-tx-3.2.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context-3.2.xsd
http://www.springframework.org/schema/mvc
http://www.springframework.org/schema/mvc/spring-mvc-3.2.xsd">  <!-- demo2 -->  <bean name="product" class="cn.redis.model.Product"></bean>  </beans></span>  

该bean的定义告诉Spring通过无参的构造来初始化product类。如果不存在该构造器（如果类作者重载了构造器，且没有显示声明默认构造器），则Spring将抛出一个异常。

ps：

应采用id或者name属性表示一个bean。为了让Spring创建一个Product实例，应将Bean定义的name值“product”（具体实践也可以是id值）和Product类型作为参数传递给ApplicationContext的getBean方法。

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   public void test1(){  ApplicationContext context = new ClassPathXmlApplicationContext(new String[]{"config1.xml"});  Product product = context.getBean("Product",Product.class);  product.setName("www");  System.out.println("product:"+product.getName());  }  

    通过工厂方法创建一个bean实例

   除了通过类的构造器方法Spring还同样支持通过调用一个工厂的方法来初始化类。下面的bean定义展示了通过工厂方法来实例化java.uti.Calendar

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

   DestroyMethod的使用

   有时，我们希望在一些类被销毁前能执行一些方法，Spring考虑到了这样的需求，可以在bean定义中配置destroy-method属性，来指定在销毁前要执行的方法。

   下面的例子中，配置Spring通过java.util.concurrent.Executors的静态方法newCachedThreadPool来创建一个java.util.concurrent.ExecutorService实例，并指定了destroy-method属性为shutdown方法。这样，Spring会在销毁ExecutorService实例前调用shutdown方法。

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

   向构造器传递参数

   spring 支持通过带参数的构造器来初始化类

   proudct类

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   public class Product implements Serializable {  private static final long serialVersionUID = 1L;  private String name;  private String description;  private float price;  public Product() {  }  public Product(String name,String description,float price) {
   <span style="white-space:pre">        </span>this.name=name;
   <span style="white-space:pre">        </span>this.description = description;
   <span style="white-space:pre">        </span>this.price=price;
   <span style="white-space:pre">    </span>}  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;  }  }  如下定义展示了如何通过参数名传递参数
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   <bean name="featuredProduct" class="cn.redis.model.Product">  <constructor-arg name="name" value="Ultimate Olive Oil" />  <constructor-arg name="description" value="The purest olive oil on the market" />  <constructor-arg name="price" value="9.95" />  </bean>
   这样在创建product实例时，Spring会调用如下构造器。
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   public Product(String name,String description,float price) {  this.name=name;  this.description = description;  this.price=price;  }  

   除了通过名称传递参数外，Spring还支持通过指数方式传递参数，具体如下：

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   <bean name="featuredProduct2" class="cn.redis.model.Product">  <constructor-arg index="0" value="Ultimate Olive Oil" />  <constructor-arg index="1"  value="The purest olive oil on the market" />  <constructor-arg index="2" value="9.95" />  </bean>  

   Setter 方式依赖注入

   下面以employee类和address类为例，说明setter方式依赖注入。

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   package cn.redis.model;  public class Employee {  private String firstName;  private String lastName;  private Address homeAddress;  public Employee() {  }  public Employee(String firstName, String lastName, Address homeAddress) {  super();  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 "Employee [firstName=" + firstName + ", lastName=" + lastName  + ", homeAddress=" + homeAddress + "]";  }  }  

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   package cn.redis.model;  public class Address {  private String line1;  private String city;  private String state;  private String zipCode;  private String country;  public Address(String line1, String city, String state, String zipCode,  String country) {  super();  this.line1 = line1;  this.city = city;  this.state = state;  this.zipCode = zipCode;  this.country = country;  }  // getters and setters onitted  @Override  public String toString() {  return "Address [line1=" + line1 + ", city=" + city + ", state="  + state + ", zipCode=" + zipCode + ", country=" + country + "]";  }  }  

   Employee 依赖于Address类，可以通过如下配置来保证每一个Employee实例都能包含Address类

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   <bean name="simpleAddress" class="cn.redis.model.Address">  <constructor-arg name="line1" value="151 corner" />  <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="employee" class="cn.redis.model.Employee">  <constructor-arg name="firstName" ref="simpleAddress" />  <constructor-arg name="lastName" value="Junio" />  <constructor-arg name=" homeAddress " value="Moore" />  </bean>  

   simpleAddress 对象是Address类的一个实例，其通过构造器方式实例化。employee对象则通过配置property元素来调用setter方法设置值，需要注意的是，homeAddress属性配置是simpleAddress对象的引用。被引用对象的配置定义无须早于引用其对象的定义。本例中，employee1对象可以出现在simpleAdress 对象定义之前。

   构造器方式的依赖注入

   我们还可以将Address对象通过构造器注入，如下所示

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   <bean name="employee2" class="cn.redis.model.Employee">  <constructor-arg name="homeAddress"  ref="simpleAddress"/>  <constructor-arg name="firstName"  value="w"/>  <constructor-arg name="lastName"  value="qq"/>  </bean>  

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   <bean name="simpleAddress" class="cn.redis.model.Address">  <constructor-arg name="line1" value="151 corner" />  <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>