Spring为singleton bean注入prototype bean
目录
- 环境
- 准备
- 测试0
- 测试1
- 测试2
- 测试3
注:不想看具体代码的话,可以直接看每个测试的总结。
环境
- Ubuntu 22.04
- IntelliJ IDEA 2022.1.3
- JDK 17.0.3
- Spring 5.3.21
准备
创建Maven项目 test0707
。
修改 pom.xml
文件,添加依赖:
...... <!-- https://mvnrepository.com/artifact/junit/junit --> <dependency> <groupId>junit</groupId> <artifactId>junit</artifactId> <version>4.13.2</version> <scope>test</scope> </dependency> <!-- https://mvnrepository.com/artifact/org.springframework/spring-webmvc --> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-webmvc</artifactId> <version>5.3.21</version> </dependency> ......
创建如下POJO:
Book
:Book接口;PlayBook
:Book实现类;StudyBook
:Book实现类;Student1
:Student1持有Book;
package pojo; public interface Book { public void show(); }
package pojo; public class PlayBook implements Book{ public PlayBook() { System.out.println("PlayBook constructor"); } @Override public void show() { System.out.println("Play book!"); } }
package pojo; public class StudyBook implements Book{ public StudyBook() { System.out.println("StudyBook constructor"); } @Override public void show() { System.out.println("Study book!"); } }
package pojo; public class Student1 { private String name; private Book book; public void setName(String name) { this.name = name; } public void setBook(Book book) { this.book = book; } public Book getBook() { return book; } public Student1() { System.out.println("Student1 constructor"); } public void readBook() { System.out.println("I am " + name); book.show(); } }
在 src/main/resources
目录下创建 applicationContext.xml
文件:
<?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="playBook" class="pojo.PlayBook" scope="prototype"/> <bean id="studyBook" class="pojo.StudyBook" scope="prototype"/> <bean id="student1" class="pojo.Student1"> <property name="name" value="Jerry"/> <property name="book" ref="playBook"/> </bean> </beans>
在 src/test/java
目录下创建测试:
public class Test0707 {}
测试0
创建测试用例:
@Test public void test0() { var ctx = new ClassPathXmlApplicationContext("applicationContext.xml"); }
运行测试,如下:
Student1 constructor
PlayBook constructor
总结:
- singleton的bean会在Spring初始化时创建实例(如本例中的
student1
) - ;prototype的bean不会在Spring初始化时创建实例(如本例中的
studyBook
);若把A注入B(B是singleton), - 则A在Spring初始化时随着B一起创建实例(如本例中的
playBook
)。 - 接上条,若把A注入B(B是singleton),如果A是singleton,则A在B之前创建实例。如果A是prototype,则A在B之后创建实例;
测试1
创建测试用例:
@Test public void test1() { var ctx = new ClassPathXmlApplicationContext("applicationContext.xml"); System.out.println("before getBean student1 playBook"); var student1 = ctx.getBean("student1", Student1.class); var student2 = ctx.getBean("student1", Student1.class); System.out.println(student1 == student2); var book1 = ctx.getBean("playBook", PlayBook.class); var book2 = ctx.getBean("playBook", PlayBook.class); System.out.println(book1 == book2); }
运行测试,如下:
Student1 constructor
PlayBook constructor
before getBean student1 playBook
true
PlayBook constructor
PlayBook constructor
false
总结:
singleton的bean,只在Spring初始化时创建实例, getBean()
不会创建实例;prototype的bean,不在Spring初始化时创建实例(注入例外),每次 getBean()
都会创建实例;
测试2
创建测试用例:
@Test public void test2() { var ctx = new ClassPathXmlApplicationContext("applicationContext.xml"); System.out.println("before getBean student1"); var student1 = ctx.getBean("student1", Student1.class); var student2 = ctx.getBean("student1", Student1.class); System.out.println(student1 == student2); System.out.println(student1.getBook() == student2.getBook()); }
运行测试,如下:
Student1 constructor
PlayBook constructor
before getBean student1
true
true
总结:
把prototype的bean注入到singleton,多次调用 getBean()
获取后者时,得到的是同一实例,同理,其持有的前者,也是同一实例。
测试3
多次调用 getBean()
方法获取singleton bean时,对于所注入的prototype的bean,如果希望每次都获取一个新的bean实例,可以使用 lookup-method
来配置。
例如:
<lookup-method name="getBook" bean="playBook"/>
完整例子如下:
创建POJO Student2
:
package pojo; public abstract class Student2 { private String name; // private Book book; public void setName(String name) { this.name = name; } // public void setBook(Book book) { // this.book = book; // } // // public Book getBook() { // return book; // } public abstract Book getBook(); public Student2() { System.out.println("Student2 constructor"); } public void readBook() { System.out.println("I am " + name); // book.show(); getBook().show(); } }
在 applicationContext.xml
文件中注册bean:
<bean id="student2" class="pojo.Student2"> <property name="name" value="Jerry"/> <!-- <property name="book" ref="playBook"/>--> <lookup-method name="getBook" bean="playBook"/> </bean>
创建测试用例:
@Test public void test3() { var ctx = new ClassPathXmlApplicationContext("applicationContext.xml"); System.out.println("before getBean student2"); var student1 = ctx.getBean("student2", Student2.class); var student2 = ctx.getBean("student2", Student2.class); System.out.println(student1 == student2); System.out.println(student1.getBook() == student2.getBook()); }
运行测试,如下:
......
Student2 constructor
before getBean student2
true
PlayBook constructor
PlayBook constructor
false
总结:
Student2
是抽象类,getBook()
是抽象方法;Student2
并不持有Book,只需使用getBook()
方法来得到Book;- 在Spring配置中使用
lookup-method
来指定方法名字(name
属性)和所获取的bean(bean
属性);getBook()
是Spring实现的,相当于调用了 getBean()
方法来得到实例,所以每次都能获取一个新的实例(当然前提是bean必须是prototype的);- singleton bean在Spring初始化时创建实例,lookup的bean不会随着一起创建实例,只有在显式调用lookup方法时才会
getBean()
(类似懒加载);
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