Spring Framework 源码学习笔记（六）

RiemannHypothesis

发布于 2022-08-19 16:01:19

1800

发布于 2022-08-19 16:01:19

文章被收录于专栏：Elixir

Chapter 06 - @Autowire 及 Aware

Section 01 - @Autowire的位置

@Autowire出了可以放在属性上，还可以放置的setter方法上以及有参构造方法上，都可以实现Bean的自动装配

@Autowire在Setter方法上 首先给两个实体类增加@Component注解，给User增加一个Address的属性

@Component
public class User {

    private String username;
    private String password;

    private Address address;

    public User() {
        System.out.println("User 无参数构造方法被调用");
    }

    public Address getAddress() {
        return address;
    }

    @Autowired
    public void setAddress(Address address) {
        this.address = address;
    }


    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    @Override
    public String toString() {
        return "User{" +
                "username='" + username + ''' +
                ", password='" + password + ''' +
                ", address=" + address +
                '}';
    }
}

@Component
public class Address {

    private Integer id;
    private String addressDetail;

    public Address() {
        System.out.println("Address空参构造方法被调用");
    }

    public Address(Integer id, String addressDetail) {
        System.out.println("Address有参数构造方法被调用");
        this.id = id;
        this.addressDetail = addressDetail;
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getAddressDetail() {
        return addressDetail;
    }

    public void setAddressDetail(String addressDetail) {
        this.addressDetail = addressDetail;
    }

    @PostConstruct
    public void init(){
        System.out.println("Address Bean 的初始化方法");
    }

    @PreDestroy
    public void destroy(){
        System.out.println("Address Bean的销毁方法");
    }
}

在BeanAutoAssembleConfig配置扫描entity包，将User和Address注册到容器中

@ComponentScan(basePackages = {"com.citi.dao","com.citi.service","com.citi.controller","com.citi.entity"})
public class BeanAutoAssembleConfig {

    //@Primary
    @Bean("personDao2")
    public PersonDao personDao(){
        return new PersonDao();
    }
}

修改BeanAutoAssembleConfigTest，执行测试

public class BeanAutoAssembleConfitTest {

    @Test
    public void isSameBean(){
        ApplicationContext context = new AnnotationConfigApplicationContext(BeanAutoAssembleConfig.class);
        System.out.println("IoC容器初始化完成");

        Address address = context.getBean("address",Address.class);
        System.out.println(address);

        User user = context.getBean("user", User.class);
        System.out.println(user.getAddress());

        // 关闭容器
        ((AnnotationConfigApplicationContext)context).close();
    }
}

执行测试，控制台打印，Address可以成功注入到User中

@Autowire在有参数的构造方法上 新增加一个只包含Address参数的User构造方法，在方法上面增加@Autowire注解，同时将Setter方法的@Autowire注解注释

@Component
public class User {

    private String username;
    private String password;

    private Address address;

    public User() {
        System.out.println("User 无参数构造方法被调用");
    }

    @Autowired
    public User(Address address) {
        System.out.println("User有参数构造方法被调用");
        this.address = address;
    }

    public Address getAddress() {
        return address;
    }

    //@Autowired
    public void setAddress(Address address) {
        this.address = address;
    }


    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    @Override
    public String toString() {
        return "User{" +
                "username='" + username + ''' +
                ", password='" + password + ''' +
                ", address=" + address +
                '}';
    }
}

其他地方不用修改，执行测试类，控制台打印如下，可以成功装配Bean，并且是通过调用User的Setter方法实现的

参考@Autowire源码，@Autowire注解可以放在构造方法，setter方法，属性及方法的参数上

Section 02 - Spring的Aware接口

修改entity包中的Product实体类，实现ApplicationContextAware，BeanNameAware，EmbeddedValueResolverAware接口，并实现接口中的方法

@Component
public class Product implements ApplicationContextAware, BeanNameAware, EmbeddedValueResolverAware {

    private Integer id;

    private String name;

    private Integer price;

    private ApplicationContext applicationContext;

    @Override
    public void setBeanName(String name) {
        System.out.println("beanName为:" + name);
    }

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        System.out.println("IoC容器为:" + applicationContext);
    }

    @Override
    public void setEmbeddedValueResolver(StringValueResolver resolver) {
        String result = resolver.resolveStringValue("操作系统为:${os.name}");
        System.out.println(result);
    }
    
    // 省略getter/setter/toString方法
}

在config包中增加一个配置类BeanAwareConfig，使用@ComponentScan将entity包中的类注册到容器中

@Configuration
@ComponentScan(value = {"com.citi.entity"})
public class BeanAwareConfig {
}

在test包中增加一个测试类

public class BeanAwareConfigTest {

    @Test
    public void testAware(){

        ApplicationContext context = new AnnotationConfigApplicationContext(BeanAutoAssembleConfig.class);
        System.out.println("IoC容器初始化完成");

        Product product = context.getBean("product", Product.class);
        System.out.println(product);

        // 关闭容器
        ((AnnotationConfigApplicationContext)context).close();
    }
}

执行测试，控制台输出如下

控制台输出了IoC容器，beanName等信息，这些都是Spring 底层组件提供的，也就是说如果想要把Spring底层的组件注入到自定义的Bean中，需要实现相应的Aware接口，如ApplicationContextAware可以提供IoC容器，这些Aware类都是相关的Processor的后置处理器来处理。

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原始发表：2021-12-24，如有侵权请联系 cloudcommunity@tencent.com 删除

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