Spring学习--xml 中 Bean 的自动装配
简介
Spring IOC 容器可以自动装配 Bean。 只要在 <bean> 的 autowire 属性里指定自动装配的模式。
- byName(根据名称自动装配)：必须将目标 Bean 的名称和当前 Bean 指定的类中的 setter 名称相匹配。
- byType(根据类型自动装配)：必须目标 Bean 的类型和当前 Bean 的类型相匹配。
- Constructor(构造函数自动装配)：比较复杂，不推荐使用。
名称自动装配
1 <?xml version="1.0" encoding="UTF-8"?> 2 <beans xmlns="http://www.springframework.org/schema/beans" 3 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 4 xmlns:p="http://www.springframework.org/schema/p" 5 xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd"> 6 7 <bean id="car" class="com.itdjx.spring.beans.aotuwire.Car" p:brand="Baoma" p:price="230000" /> 8 <bean id="address" class="com.itdjx.spring.beans.aotuwire.Address" p:city="Dalian" p:street="ShaHeKou"/> 9 <bean id="person" class="com.itdjx.spring.beans.aotuwire.Person" p:name="Tom" autowire="byName"/> 10 11 </beans>
1 package com.itdjx.spring.beans.aotuwire; 2 3 /** 4 * @author Wáng Chéng Dá 5 * @create 2017-03-01 10:59 6 */ 7 public class Car { 8 9 private String brand; 10 private double price; 11 12 public String getBrand() { 13 return brand; 14 } 15 16 public void setBrand(String brand) { 17 this.brand = brand; 18 } 19 20 public double getPrice() { 21 return price; 22 } 23 24 public void setPrice(double price) { 25 this.price = price; 26 } 27 28 @Override 29 public String toString() { 30 return "Car{" + 31 "brand='" + brand + '\'' + 32 ", price=" + price + 33 '}'; 34 } 35 }
1 package com.itdjx.spring.beans.aotuwire; 2 3 /** 4 * @author Wáng Chéng Dá 5 * @create 2017-03-01 10:59 6 */ 7 public class Address { 8 9 private String city; 10 11 private String street; 12 13 public String getCity() { 14 return city; 15 } 16 17 public void setCity(String city) { 18 this.city = city; 19 } 20 21 public String getStreet() { 22 return street; 23 } 24 25 public void setStreet(String street) { 26 this.street = street; 27 } 28 29 @Override 30 public String toString() { 31 return "Address{" + 32 "city='" + city + '\'' + 33 ", street='" + street + '\'' + 34 '}'; 35 } 36 }
1 package com.itdjx.spring.beans.aotuwire; 2 3 /** 4 * @author Wáng Chéng Dá 5 * @create 2017-03-01 10:59 6 */ 7 public class Person { 8 9 private String name; 10 11 private Address address; 12 13 private Car car; 14 15 public String getName() { 16 return name; 17 } 18 19 public void setName(String name) { 20 this.name = name; 21 } 22 23 public Address getAddress() { 24 return address; 25 } 26 27 public void setAddress(Address address) { 28 this.address = address; 29 } 30 31 public Car getCar() { 32 return car; 33 } 34 35 public void setCar(Car car) { 36 this.car = car; 37 } 38 39 @Override 40 public String toString() { 41 return "Person{" + 42 "name='" + name + '\'' + 43 ", address=" + address + 44 ", car=" + car + 45 '}'; 46 } 47 }
1 package com.itdjx.spring.beans.aotuwire; 2 3 import org.springframework.context.ApplicationContext; 4 import org.springframework.context.support.ClassPathXmlApplicationContext; 5 6 /** 7 * @author Wáng Chéng Dá 8 * @create 2017-03-01 11:05 9 */ 10 public class Main { 11 12 public static void main(String[] args) { 13 ApplicationContext app = new ClassPathXmlApplicationContext("beans-aotuwire.xml"); 14 Person person = (Person) app.getBean("person"); 15 System.out.println(person); 16 } 17 }
控制台输出：
| Person{name='Tom', address=Address{city='Dalian', street='ShaHeKou'}, car=Car{brand='Baoma', price=230000.0}} |
若修改配置文件中的 address 为 address1 ：
1 <?xml version="1.0" encoding="UTF-8"?> 2 <beans xmlns="http://www.springframework.org/schema/beans" 3 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 4 xmlns:p="http://www.springframework.org/schema/p" 5 xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd"> 6 7 <bean id="car" class="com.itdjx.spring.beans.aotuwire.Car" p:brand="Baoma" p:price="230000" /> 8 <bean id="address1" class="com.itdjx.spring.beans.aotuwire.Address" p:city="Dalian" p:street="ShaHeKou"/> 9 <bean id="person" class="com.itdjx.spring.beans.aotuwire.Person" p:name="Tom" autowire="byName"/> 10 11 </beans>
控制台输出：
| Person{name='Tom', address=null, car=Car{brand='Baoma', price=230000.0}} |
出现这种状况说明自动装配没有匹配到 address 对象。id="address" 与 Person 中的 setAdress() 方法匹配。
类型自动装配
1 <?xml version="1.0" encoding="UTF-8"?> 2 <beans xmlns="http://www.springframework.org/schema/beans" 3 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 4 xmlns:p="http://www.springframework.org/schema/p" 5 xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd"> 6 7 <bean id="car" class="com.itdjx.spring.beans.aotuwire.Car" p:brand="Baoma" p:price="230000" /> 8 <bean id="address1" class="com.itdjx.spring.beans.aotuwire.Address" p:city="Dalian" p:street="ShaHeKou"/> 9 <bean id="person" class="com.itdjx.spring.beans.aotuwire.Person" p:name="Tom" autowire="byType"/> 10 11 </beans>
控制台输出：
| Person{name='Tom', address=Address{city='Dalian', street='ShaHeKou'}, car=Car{brand='Baoma', price=230000.0}} |
若是多定义几个相同的类 , 程序会出现异常。
1 <?xml version="1.0" encoding="UTF-8"?> 2 <beans xmlns="http://www.springframework.org/schema/beans" 3 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 4 xmlns:p="http://www.springframework.org/schema/p" 5 xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd"> 6 7 <bean id="car" class="com.itdjx.spring.beans.aotuwire.Car" p:brand="Baoma" p:price="230000" /> 8 <bean id="address1" class="com.itdjx.spring.beans.aotuwire.Address" p:city="Dalian" p:street="ShaHeKou"/> 9 <bean id="address" class="com.itdjx.spring.beans.aotuwire.Address" p:city="ShenYang" p:street="Dadong"/> 10 <bean id="person" class="com.itdjx.spring.beans.aotuwire.Person" p:name="Tom" autowire="byType"/> 11 12 </beans>
控制台输出：
|
警告: Exception encountered during context initialization - cancelling refresh attempt: org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'person' defined in class path resource [beans-aotuwire.xml]: Unsatisfied dependency expressed through bean property 'address'; nested exception is org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type 'com.itdjx.spring.beans.aotuwire.Address' available: expected single matching bean but found 2: address1,address |
xml 中 Bean 自动装配的缺点
- 在 Bean 配置文件里设置 autowire 属性进行自动装配将会装配 Bean 的所有属性。然而 , 若只希望装配个别属性时 , autowire 属性就不够灵活了。
- autowire 属性要么根据类型自动装配 , 要么根据名称自动装配 , 不能二者兼有。
