Spring学习--Bean 之间的关系

Bean 之间的关系：继承、依赖。

Bean 继承：

• Spring 允许继承 bean 的配置 , 被继承的 bean 称为父 bean , 继承这个父 bean 的 bean 称为子 bean。
• 子 bean 从父 bean 中继承配置 , 包括 bean 的属性配置。
• 子 bean 也可以覆盖从父 bean 继承过来的配置。
• 父 bean 可以作为配置模板 , 也可以作为 bean 实例。若只想把父 bean 作为模板 , 可以设置 <bean> 的 abstract 属性为 true , 这样 IOC容器将不会实例这个 bean。
• 并不是 <bean> 元素里的所有属性都会被继承。比如： autowire , abstract 等。
• 父 bean 的 class 属性可以忽略 , 让子 bean 指定自己的类 , 而共享相同的属性配置。但此时 abstract 必须设为 true。

 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="address" class="com.itdoc.spring.extendsinfo.Address" p:city="DaLian" p:street="ShaHeKou"/>
 8
 9     <bean id="address1" class="com.itdoc.spring.extendsinfo.Address" p:street="GanJingZi" parent="address"/>
10
11 </beans>

 1 package com.itdoc.spring.extendsinfo;
 2
 3 /**
 4  * http://www.cnblogs.com/goodcheap
 5  *
 6  * @author: Wáng Chéng Dá
 7  * @create: 2017-03-01 20:48
 8  */
 9 public class Address {
10
11     private String city;
12
13     private String street;
14
15     public String getCity() {
16         return city;
17     }
18
19     public void setCity(String city) {
20         this.city = city;
21     }
22
23     public String getStreet() {
24         return street;
25     }
26
27     public void setStreet(String street) {
28         this.street = street;
29     }
30
31     @Override
32     public String toString() {
33         return "Address{" +
34                 "city=‘" + city + ‘\‘‘ +
35                 ", street=‘" + street + ‘\‘‘ +
36                 ‘}‘;
37     }
38 }

 1 package com.itdoc.spring.extendsinfo;
 2
 3 import org.springframework.context.ApplicationContext;
 4 import org.springframework.context.support.ClassPathXmlApplicationContext;
 5
 6 /**
 7  * http://www.cnblogs.com/goodcheap
 8  *
 9  * @author: Wáng Chéng Dá
10  * @create: 2017-03-01 20:55
11  */
12 public class Main {
13
14     public static void main(String[] args) {
15         ApplicationContext app = new ClassPathXmlApplicationContext("beans_extends.xml");
16         Address address = (Address) app.getBean("address");
17         System.out.println(address);
18
19         System.out.println("-------------------");
20         address = (Address) app.getBean("address1");
21         System.out.println(address);
22
23     }
24 }

控制台输出：

 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="address" class="com.itdoc.spring.extendsinfo.Address" p:city="DaLian" p:street="ShaHeKou" abstract="true"/>
 8
 9     <bean id="address1" class="com.itdoc.spring.extendsinfo.Address" p:street="GanJingZi" parent="address"/>
10
11 </beans>

控制台输出：

原因：address 成为了模板 bean , 不可以实例化。

 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="address" p:city="DaLian" p:street="ShaHeKou"/>
 8
 9     <bean id="address1" class="com.itdoc.spring.extendsinfo.Address" p:street="GanJingZi" parent="address"/>
10
11 </beans>

 1 package com.itdoc.spring.extendsinfo;
 2
 3 import org.springframework.context.ApplicationContext;
 4 import org.springframework.context.support.ClassPathXmlApplicationContext;
 5
 6 /**
 7  * http://www.cnblogs.com/goodcheap
 8  *
 9  * @author: Wáng Chéng Dá
10  * @create: 2017-03-01 20:55
11  */
12 public class Main {
13
14     public static void main(String[] args) {
15         ApplicationContext app = new ClassPathXmlApplicationContext("beans_extends.xml");
16         Address address = (Address) app.getBean("address1");
17         System.out.println(address);
18
19     }
20 }

控制台输出：

原因：父 bean 中的 class 属性忽略 , 该 bean 必须是 abstract="true" 的。

Bean 依赖：

• Spring 允许用户通过 depends-on 属性设定 bean 前置依赖的 bean , 前置依赖的 bean 会在本 bean 实例化前创建好。
• 如果前置依赖于多个 bean , 则可以通过逗号或空格的方式配置 bean 的名称。

 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="person" class="com.itdoc.spring.extendsinfo.Person" p:name="华崽儿" p:car-ref="car" p:address-ref="address"/>
 8     <bean id="address" class="com.itdoc.spring.extendsinfo.Address" p:city="DaLian" p:street="ShaHeKou"/>
 9     <bean id="car" class="com.itdoc.spring.beans.Car" p:brand="8手奥拓" p:price="3000" p:maxSpeed="120"/>
10
11 </beans>

 1 package com.itdoc.spring.extendsinfo;
 2
 3 import com.itdoc.spring.beans.Car;
 4
 5 /**
 6  * http://www.cnblogs.com/goodcheap
 7  *
 8  * @author: Wáng Chéng Dá
 9  * @create: 2017-03-01 20:47
10  */
11 public class Person {
12
13     private String name;
14
15     private Address address;
16
17     private Car car;
18
19     public String getName() {
20         return name;
21     }
22
23     public void setName(String name) {
24         this.name = name;
25     }
26
27     public Address getAddress() {
28         return address;
29     }
30
31     public void setAddress(Address address) {
32         this.address = address;
33     }
34
35     public Car getCar() {
36         return car;
37     }
38
39     public void setCar(Car car) {
40         this.car = car;
41     }
42
43     public Person() {
44         System.out.println("I am Person Constructor...");
45     }
46
47     @Override
48     public String toString() {
49         return "Person{" +
50                 "name=‘" + name + ‘\‘‘ +
51                 ", address=" + address +
52                 ", car=" + car +
53                 ‘}‘;
54     }
55 }

 1 package com.itdoc.spring.extendsinfo;
 2
 3 /**
 4  * http://www.cnblogs.com/goodcheap
 5  *
 6  * @author: Wáng Chéng Dá
 7  * @create: 2017-03-01 20:48
 8  */
 9 public class Address {
10
11     private String city;
12
13     private String street;
14
15     public String getCity() {
16         return city;
17     }
18
19     public void setCity(String city) {
20         this.city = city;
21     }
22
23     public String getStreet() {
24         return street;
25     }
26
27     public void setStreet(String street) {
28         this.street = street;
29     }
30
31     public Address() {
32         System.out.println("I am Address Constructor...");
33     }
34
35     @Override
36     public String toString() {
37         return "Address{" +
38                 "city=‘" + city + ‘\‘‘ +
39                 ", street=‘" + street + ‘\‘‘ +
40                 ‘}‘;
41     }
42 }

 1 package com.itdoc.spring.beans;
 2
 3 /**
 4  * 集合中的对象
 5  * http://www.cnblogs.com/goodcheap
 6  *
 7  * @author: Wáng Chéng Dá
 8  * @create: 2017-02-28 19:56
 9  */
10 public class Car {
11
12     private String brand;
13
14     private double price;
15
16     private int maxSpeed;
17
18     public String getBrand() {
19         return brand;
20     }
21
22     public void setBrand(String brand) {
23         this.brand = brand;
24     }
25
26     public double getPrice() {
27         return price;
28     }
29
30     public void setPrice(double price) {
31         this.price = price;
32     }
33
34     public int getMaxSpeed() {
35         return maxSpeed;
36     }
37
38     public void setMaxSpeed(int maxSpeed) {
39         this.maxSpeed = maxSpeed;
40     }
41
42     public Car() {
43         System.out.println("I am Car Constructor...");
44     }
45
46     @Override
47     public String toString() {
48         return "Car{" +
49                 "brand=‘" + brand + ‘\‘‘ +
50                 ", price=" + price +
51                 ", maxSpeed=" + maxSpeed +
52                 ‘}‘;
53     }
54 }

 1 package com.itdoc.spring.extendsinfo;
 2
 3 import org.springframework.context.ApplicationContext;
 4 import org.springframework.context.support.ClassPathXmlApplicationContext;
 5
 6 /**
 7  * http://www.cnblogs.com/goodcheap
 8  *
 9  * @author: Wáng Chéng Dá
10  * @create: 2017-03-01 20:55
11  */
12 public class Main {
13
14     public static void main(String[] args) {
15         ApplicationContext app = new ClassPathXmlApplicationContext("beans_extends.xml");
16         Person person = (Person) app.getBean("person");
17         System.out.println(person);
18
19     }
20 }

控制台输出：

 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="person" class="com.itdoc.spring.extendsinfo.Person" p:name="华崽儿" p:car-ref="car" p:address-ref="address" depends-on="car, address"/>
 8
 9     <bean id="address" class="com.itdoc.spring.extendsinfo.Address" p:city="DaLian" p:street="ShaHeKou"/>
10
11     <bean id="car" class="com.itdoc.spring.beans.Car" p:brand="8手奥拓" p:price="3000" p:maxSpeed="120"/>
12
13 </beans>

控制台输出：

根据控制台输出我们不难看出 bean 的初始化顺序发生了改变 , 前置依赖的 bean 会在本 bean 实例化前创建好。