Spring源码-createBeanInstance方法Supplier创建bean实例

一、例子

Supplier.java

@FunctionalInterface
public interface Supplier {

/**
* Gets a result.
*
* @return a result
*/
T get();
}

java8以后提供的接口，可以看作是生产者，返回一个对象。

User.java

public class User {
private Integer id;

private String name;

private Integer age;

public Integer getId() {
return id;
}

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

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public Integer getAge() {
return age;
}

public void setAge(Integer age) {
this.age = age;
}

@Override
public String toString() {
final StringBuffer sb = new StringBuffer("User{");
sb.append("id=").append(id);
sb.append(", name='").append(name).append(''');
sb.append(", age=").append(age);
sb.append('}');
return sb.toString();
}
}

SupplierBeanFactoryPostProcessor.java

public class SupplierBeanFactoryPostProcessor implements BeanFactoryPostProcessor {
@Override
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
AbstractBeanDefinition user = (AbstractBeanDefinition)beanFactory.getBeanDefinition("user");
user.setInstanceSupplier(()->{
User user1 = new User();
return user1;
});
}
}

supplier.xml

Test.java

public class Test {
public static void main(String[] args) {
ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext("supplier.xml");

User user = applicationContext.getBean(User.class);
System.out.println(user);
}
}

二Spring源码解读Supplier创建bean实例

AbstractAutowireCapableBeanFactory的createBeanInstance：

Supplier<?> instanceSupplier = mbd.getInstanceSupplier();
if (instanceSupplier != null) {
return obtainFromSupplier(instanceSupplier, beanName);
}

protected BeanWrapper obtainFromSupplier(Supplier<?> instanceSupplier, String beanName) {
Object instance;

String outerBean = this.currentlyCreatedBean.get();
this.currentlyCreatedBean.set(beanName);
try {
instance = instanceSupplier.get();
}
finally {
if (outerBean != null) {
this.currentlyCreatedBean.set(outerBean);
}
else {
this.currentlyCreatedBean.remove();
}
}

if (instance == null) {
instance = new NullBean();
}
BeanWrapper bw = new BeanWrapperImpl(instance);
initBeanWrapper(bw);
return bw;
}

如果AbstractBeanDefinition的instanceSupplier不为null，则调用instanceSupplier创建bean实例。