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這篇文章主要介紹了Spring如何使用注解的方式創(chuàng)建bean,文中通過示例代碼介紹的非常詳細(xì),對(duì)大家的學(xué)習(xí)或者工作具有一定的參考學(xué)習(xí)價(jià)值,需要的朋友可以參考下
第一種使用配置類的方式
1、創(chuàng)建一個(gè)bean
package com.springbean; public class Person { private String name; private Integer age ; public Person(String name, Integer age) { this.name = name; this.age = age; } public void setName(String name) { this.name = name; } public void setAge(Integer age) { this.age = age; } public String getName() { return name; } public Integer getAge() { return age; } @Override public String toString() { return "Person{" + "name='" + name + '\'' + ", age=" + age + '}'; } }
2、創(chuàng)建配置類:
import com.springbean.Person; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; @Configuration public class PersonConfig { @Bean //@Bean("myperson") 這是設(shè)置bean的名字 public Person person(){ System.out.println("已經(jīng)創(chuàng)建實(shí)例"); return new Person("張三",20); } }
3、測(cè)試
import com.spring.config.PersonConfig; import com.springbean.Person; import org.springframework.context.ApplicationContext; import org.springframework.context.annotation.AnnotationConfigApplicationContext; public class ApplicationTest { public static void main(String[] args) { ApplicationContext applicationContext = new AnnotationConfigApplicationContext(PersonConfig.class); Person bean = applicationContext.getBean(Person.class); System.out.println(bean); //獲取bean的類型,默認(rèn)是方法名,需要修改就在配置類中@Bean里面加上名字 String[] beanNamesForType = applicationContext.getBeanNamesForType(Person.class); for (String beanType : beanNamesForType){ System.out.println(beanType); } } }
和xml配置文件一樣,默認(rèn)的bean是單例的,如果需要改變?yōu)閜rototype,xml配置文件里是加上scope="prototype",這里PersonConfig配置類中需要加上注解@Scope("prototype")。
介紹一下bean的幾種類型的作用域。
不加注解測(cè)試:
ApplicationContext applicationContext = new AnnotationConfigApplicationContext(PersonConfig.class); Person bean = applicationContext.getBean(Person.class); Person bean2 = applicationContext.getBean(Person.class); System.out.println(bean==bean2);//打印結(jié)果為true
加上注解@Scope("prototype")測(cè)試:
ApplicationContext applicationContext = new AnnotationConfigApplicationContext(PersonConfig.class); Person bean = applicationContext.getBean(Person.class); Person bean2 = applicationContext.getBean(Person.class); System.out.println(bean==bean2); //打印結(jié)果為fale
我們也可以改變單例時(shí)ioc加載的時(shí)候就創(chuàng)建實(shí)例,只要在我們的PersonConfig配置類中加上@Lazy注解,使用懶加載。測(cè)試
public class ApplicationTest { public static void main(String[] args) { ApplicationContext applicationContext = new AnnotationConfigApplicationContext(PersonConfig.class); /* Person bean = applicationContext.getBean(Person.class); Person bean2 = applicationContext.getBean(Person.class); System.out.println(bean==bean2);*/ /* String[] beanNamesForType = applicationContext.getBeanNamesForType(Person.class); for (String beanType : beanNamesForType){ System.out.println(beanType); }*/ } }
這是時(shí)打印欄將不會(huì)打印出“已經(jīng)創(chuàng)建實(shí)例”,就實(shí)現(xiàn)的單例情況下的懶加載。
第二種使用@import注解的方式
新建一個(gè)student類
public class Student { }
在配置類PersonConfig上使用@Import注解,這里面可以傳入一個(gè)數(shù)組,用大括號(hào){}
@Configuration @Import({Student.class}) public class PersonConfig {
測(cè)試:
public class DemoTest { ApplicationContext applicationContext = new AnnotationConfigApplicationContext(PersonConfig.class); @Test public void test(){ Student bean = applicationContext.getBean(Student.class); System.out.println(bean); } }
打印結(jié)果:com.springbean.Student@2c34f934 ,注入成功
還可以在@Import中加入ImportSelector的實(shí)現(xiàn)類來實(shí)現(xiàn)bean的注入
創(chuàng)建Parent和Teacher類
public class Parent { } public class Teacher { }
創(chuàng)建ImportSelector的實(shí)現(xiàn)類MyImportSelector,返回需要注入的bean,這里是全類名
public class myImportSelector implements ImportSelector{ @Override public String[] selectImports(AnnotationMetadata annotationMetadata) { return new String[]{"com.springbean.Parent","com.springbean.Teacher"}; } }
修改PersonConfig,這里傳入實(shí)現(xiàn)類MyImportSelector
@Configuration @Import({Student.class, myImportSelector.class}) public class PersonConfig {
測(cè)試:
Parent parent = applicationContext.getBean(Parent.class); Teacher teacher = applicationContext.getBean(Teacher.class); System.out.println(parent); System.out.println(teacher);
打印結(jié)果:
com.springbean.Parent@3b2cf7ab com.springbean.Teacher@2aa5fe93
以上就是本文的全部內(nèi)容,希望對(duì)大家的學(xué)習(xí)有所幫助,也希望大家多多支持億速云。
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