Java high-frequency basic interview questions——(7)

1. What are the benefits of using the Spring framework?

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Lightweight: Spring is lightweight, and the basic version is about 2MB.

Inversion of control: Spring achieves loose coupling through inversion of control. Objects give their dependencies instead of creating or finding dependent objects.

Aspect-oriented programming (AOP): Spring supports aspect-oriented programming and separates application business logic and system services.

Container: Spring contains and manages the life cycle and configuration of objects in the application.

MVC framework: Spring’s WEB framework is a well-designed framework and a good alternative to the Web framework.

Transaction management: Spring provides a continuous transaction management interface that can be extended from local transactions to global transactions (JTA).

Exception handling: Spring provides a convenient API to convert technology-specific exceptions (such as those thrown by JDBC, Hibernate or JDO) into consistent unchecked exceptions.

2. What is the usual implementation of ApplicationContext?

FileSystemXmlApplicationContext: This container loads the definition of beans from an XML file, and the complete XML Bean configuration file The pathname must be provided to its constructor.

ClassPathXmlApplicationContext: This container also loads beans definitions from an XML file. Here, you need to set the classpath correctly because this container will look for bean configurations in the classpath.

WebXmlApplicationContext: This container loads an XML file that defines all the beans of a WEB application.

3. What is Spring’s dependency injection? What methods are there for dependency injection?

Dependency injection is an aspect of IOC and a common concept. It has many interpretations. The concept is that you don't create the object, you just describe how it is created. You do not assemble your components and services directly in the code, but you must describe which components require which services in the configuration file, and then a container (IOC container) is responsible for assembling them.

Constructor dependency injection: Constructor dependency injection is implemented by the container triggering the constructor of a class. The class has a series of parameters, each parameter representing a dependency on other classes.

Setter method injection: Setter method injection is when the container instantiates a bean by calling the parameter-less constructor or parameter-less static factory method, and then calls the setter method of the bean, which implements setter-based dependency injection.

4. What are Spring beans?

Spring beans are the java objects that form the backbone of Spring applications. They are initialized, assembled, and managed by the Spring IOC container. These beans are created from metadata configured in the container. For example, defined in the form of in an XML file.

The beans defined by the Spring framework are all single beans. There is an attribute "singleton" in the bean tag. If it is assigned to TRUE, the bean is a singleton, otherwise it is a prototype bean. The default is TRUE, so all beans in the Spring framework are singletons by default.

5. Explain the scope of several beans supported by Spring.

The Spring framework supports the following five bean scopes:

Singleton: The bean has only one instance in each Spring ioc container.

prototype: A bean definition can have multiple instances.

request: Each http request will create a bean. This scope is only valid in the case of web-based Spring ApplicationContext.

Session: In an HTTP Session, a bean definition corresponds to an instance. This scope is only valid in the case of web-based Spring ApplicationContext.

global-session: In a global HTTP Session, a bean definition corresponds to an instance. This scope is only valid in the case of web-based Spring ApplicationContext.

The default scope of Spring bean is Singleton.

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6. Explain beans in Spring framework life cycle.

Spring container reads the bean definition from the XML file and instantiates the bean.

Spring fills in all properties according to the bean definition.

If the bean implements the BeanNameAware interface, Spring passes the bean's ID to the setBeanName method.

If the Bean implements the BeanFactoryAware interface, Spring passes the beanfactory to the setBeanFactory method.

If there are any BeanPostProcessors associated with the bean, Spring will call them within the postProcesserBeforeInitialization() method.

If the bean implements InitializingBean, call its afterPropertySet method. If the bean declares an initialization method, call this initialization method.

If there are BeanPostProcessors associated with the bean, the postProcessAfterInitialization() method of these beans will be called.

If the bean implements DisposableBean, it will call the destroy() method.

7. How to inject a java collection in Spring?

Spring provides the following configuration elements for collections:

The type is used to inject a list of values, allowing the same value.

The type is used to inject a set of values, and the same value is not allowed.

The

The type is used to inject a set of key-value pairs. Both keys and values ​​can only be of type String.

8. Explain different ways of automatic assembly.

There are five automatic assembly methods, which are used to guide the Spring container to use automatic assembly for dependency injection.

NO: The default method is not automatic assembly, and the REF attribute is set up by explicitly setting.

byName: Through automatic assembly of parameter names, the Spring container finds in the configuration file that the autowire attribute of the bean is set to byname, and then the container tries to match and assemble a bean with the same name as the bean's attribute.

byType:: Through automatic assembly of parameter types, the Spring container finds that the bean's autowire attribute is set to byType in the configuration file, and then the container tries to match and assemble beans of the same type as the bean's attributes. If more than one bean meets the criteria, an error is thrown.

Constructor: This method is similar to byType, but it must be provided to the constructor parameter. If there is no determined constructor parameter type with parameters, an exception will be thrown.

                           autodetect: First try to use constructor to automatically assemble. If it doesn’t work, use byType method.

9. What are the advantages of Spring framework transaction management?

It provides an unchanging programming model for different transaction APIs such as JTA, JDBC, Hibernate, JPA and JDO.

It provides a simple API for programmatic transaction management instead of some complex transaction APIs such as

It supports declarative transaction management.

It is well integrated with Spring's various data access abstraction layers.

10. What is Spring annotation configuration based on Java? Give some examples of annotations.

Java-based configuration allows you to configure a small number of Java annotations Do most of your Spring configuration without the help of XML files.

Take the @Configuration annotation as an example. It is used to mark that a class can be used as a bean definition and used by the Spring IOC container. Another example is the @Bean annotation, which indicates that this method will return an object and register it as a bean in the Spring application context.

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