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Spring中怎么利用注解的方式創(chuàng)建bean,相信很多沒有經(jīng)驗(yàn)的人對此束手無策,為此本文總結(jié)了問題出現(xiàn)的原因和解決方法,通過這篇文章希望你能解決這個(gè)問題。
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;@Configurationpublic 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。
singleton:單實(shí)例(默認(rèn)),ioc容器啟動(dòng)時(shí)就會(huì)創(chuàng)建對象放到ioc容器中,以后每次獲取都是直接從ioc容器中獲取,ioc容器可以簡單理解為map prototype:多實(shí)例(原型),ioc容器啟動(dòng)并不會(huì)去調(diào)用方法創(chuàng)建對象,而是每次我們獲取對象的時(shí)候,才會(huì)調(diào)用方法去創(chuàng)建。 requst:同一次請求創(chuàng)建一個(gè)實(shí)例 session:同一個(gè)session創(chuàng)建一個(gè)實(shí)例
不加注解測試:
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@3b2cf7abcom.springbean.Teacher@2aa5fe93
看完上述內(nèi)容,你們掌握Spring中怎么利用注解的方式創(chuàng)建bean的方法了嗎?如果還想學(xué)到更多技能或想了解更多相關(guān)內(nèi)容,歡迎關(guān)注億速云行業(yè)資訊頻道,感謝各位的閱讀!
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