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Spring怎样使用注解的方式创建bean

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这篇文章主要介绍了Spring如何使用注解的方式创建bean,文中通过示例代码介绍的非常详细,对大家的学习或者工作具有一定的参考学习价值,需要的朋友可以参考下

第一种使用配置类的方式

1、创建一个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、创建配置类:

import com.springbean.Person;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class PersonConfig {

  @Bean  //@Bean("myperson") 这是设置bean的名字
  public Person person(){   System.out.println("已经创建实例");
return new Person("张三",20); } }

3、测试

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);

    //获取bean的类型,默认是方法名,需要修改就在配置类中@Bean里面加上名字

    String[] beanNamesForType = applicationContext.getBeanNamesForType(Person.class);
    for (String beanType : beanNamesForType){
      System.out.println(beanType);
    }
  } 
}

和xml配置文件一样,默认的bean是单例的,如果需要改变为prototype,xml配置文件里是加上scope="prototype",这里PersonConfig配置类中需要加上注解@Scope("prototype")。

介绍一下bean的几种类型的作用域。

不加注解测试:

ApplicationContext applicationContext = new AnnotationConfigApplicationContext(PersonConfig.class);
    Person bean = applicationContext.getBean(Person.class);
    Person bean2 = applicationContext.getBean(Person.class);
    System.out.println(bean==bean2);//打印结果为true

加上注解@Scope("prototype")测试:

ApplicationContext applicationContext = new AnnotationConfigApplicationContext(PersonConfig.class);
    Person bean = applicationContext.getBean(Person.class);
    Person bean2 = applicationContext.getBean(Person.class);
    System.out.println(bean==bean2);
//打印结果为fale

我们也可以改变单例时ioc加载的时候就创建实例,只要在我们的PersonConfig配置类中加上@Lazy注解,使用懒加载。测试

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);
    }*/
  }
}

这是时打印栏将不会打印出“已经创建实例”,就实现的单例情况下的懒加载。

第二种使用@import注解的方式

新建一个student类

public class Student {
}

在配置类PersonConfig上使用@Import注解,这里面可以传入一个数组,用大括号{}

@Configuration
@Import({Student.class})
public class PersonConfig {

测试:

public class DemoTest {

  ApplicationContext applicationContext = new AnnotationConfigApplicationContext(PersonConfig.class);

  @Test
  public void test(){

    Student bean = applicationContext.getBean(Student.class);
    System.out.println(bean);
  }
}

打印结果:com.springbean.Student@2c34f934 ,注入成功

还可以在@Import中加入ImportSelector的实现类来实现bean的注入

创建Parent和Teacher类

public class Parent {
}

public class Teacher {
}

创建ImportSelector的实现类MyImportSelector,返回需要注入的bean,这里是全类名

public class myImportSelector implements ImportSelector{
  @Override
  public String[] selectImports(AnnotationMetadata annotationMetadata) {

    return new String[]{"com.springbean.Parent","com.springbean.Teacher"};
  }
}

修改PersonConfig,这里传入实现类MyImportSelector

@Configuration
@Import({Student.class, myImportSelector.class})
public class PersonConfig {

测试:

Parent parent = applicationContext.getBean(Parent.class);
    Teacher teacher = applicationContext.getBean(Teacher.class);
    System.out.println(parent);
    System.out.println(teacher);

打印结果:

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