How to get bean using application context in spring boot

问题

I am developing a SpringBoot project and I want to get the bean by its name using applicationContext. I have tried many solution from web but could not succeed. My Requirement is that I have a controller

ControllerA

and inside the controller I have a method getBean(String className). I want to get instance of registered bean. I have hibernate entities and I want to get an instance of the bean by passing the name of class only in getBean method.

Please help if someone know the solution.

回答1:

You can Autowire the ApplicationContext, either as a field

@Autowired
private ApplicationContext context;

or a method

@Autowired
public void context(ApplicationContext context) { this.context = context; }

Finally use

context.getBean(SomeClass.class)

回答2:

You can use ApplicationContextAware.

ApplicationContextAware:

Interface to be implemented by any object that wishes to be notified of the ApplicationContext that it runs in. Implementing this interface makes sense for example when an object requires access to a set of collaborating beans.

There are a few methods for obtaining a reference to the application context. You can implement ApplicationContextAware as in the following example:

package hello;

import org.springframework.beans.BeansException;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;

@Component
public class ApplicationContextProvider implements ApplicationContextAware {

    private ApplicationContext applicationContext;

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        this.applicationContext = applicationContext;
    } 

 public ApplicationContext getContext() {
        return applicationContext;
    }

}

Update:

When Spring instantiates beans, it looks for ApplicationContextAware implementations, If they are found, the setApplicationContext() methods will be invoked.

In this way, Spring is setting current applicationcontext.

Code snippet from Spring's source code:

private void invokeAwareInterfaces(Object bean) {
        .....
        .....
 if (bean instanceof ApplicationContextAware) {                
  ((ApplicationContextAware)bean).setApplicationContext(this.applicationContext);
   }
}

Once you get the reference to Application context, you get fetch the bean whichever you want by using getBean().

回答3:

actually you want to get the object from the Spring engine, where the engine already maintaining the object of your required class at that starting of the spring application(Initialization of the Spring engine).Now the thing is you just have to get that object to a reference.

in a service class

@Autowired
private ApplicationContext context;

SomeClass sc = (SomeClass)context.getBean(SomeClass.class);

now in the reference of the sc you are having the object. Hope explained well. If any doubt please let me know.

回答4:

If you are inside of Spring bean (in this case @Controller bean) you shouldn't use Spring context instance at all. Just autowire className bean directly.

BTW, avoid using field injection as it's considered as bad practice.

回答5:

You can use the ApplicationContextAware class that can provide the application context.

public class ApplicationContextProvider implements ApplicationContextAware {

    private static ApplicationContext ctx = null;

    public static ApplicationContext getApplicationContext() {
        return ctx;
    }

    @Override
    public void setApplicationContext(final ApplicationContext ctx) throws BeansException {
        ApplicationContextProvider.ctx = ctx;
    }

    /**
     * Tries to autowire the specified instance of the class if one of the specified
     * beans which need to be autowired are null.
     *
     * @param classToAutowire        the instance of the class which holds @Autowire
     *                               annotations
     * @param beansToAutowireInClass the beans which have the @Autowire annotation
     *                               in the specified {#classToAutowire}
     */
    public static void autowire(Object classToAutowire, Object... beansToAutowireInClass) {
        for (Object bean : beansToAutowireInClass) {
            if (bean == null) {
                ctx.getAutowireCapableBeanFactory().autowireBean(classToAutowire);
            }
        }
    }

}

回答6:

Just use:

org.springframework.beans.factory.BeanFactory#getBean(java.lang.Class)

Example:

@Component
public class Example {

    @Autowired
    private ApplicationContext context;

    public MyService getMyServiceBean() {
        return context.getBean(MyService.class);
    }

    // your code uses getMyServiceBean()
}

回答7:

You can use ServiceLocatorFactoryBean. First you need to create an interface for your class

public interface YourClassFactory {
    YourClass getClassByName(String name);
}

Then you have to create a config file for ServiceLocatorBean

@Configuration
@Component
public class ServiceLocatorFactoryBeanConfig {

    @Bean
    public ServiceLocatorFactoryBean serviceLocatorBean(){
        ServiceLocatorFactoryBean bean = new ServiceLocatorFactoryBean();
        bean.setServiceLocatorInterface(YourClassFactory.class);
        return bean;
    }
}

Now you can find your class by name like that

@Autowired
private YourClassfactory factory;

YourClass getYourClass(String name){
    return factory.getClassByName(name);
}

来源：https://stackoverflow.com/questions/34088780/how-to-get-bean-using-application-context-in-spring-boot