This is a summary of some of the most important questions concerning the Spring Framework, that you may be asked to answer in an interview or in an interview test procedure! There is no need to worry for your next interview test, because Java Code Geeks are here for you!
The majority of the things you may be asked is collected in the list below. All core modules, from basic Spring functionality such as Spring Beans, up to Spring MVC framework are presented and described in short. After checking the interview questions, you should check our Spring Tutorials page.
So, let’s go…!
Spring is an open source development framework for Enterprise Java. The core features of the Spring Framework can be used in developing any Java application, but there are extensions for building web applications on top of the Java EE platform. Spring framework targets to make Java EE development easier to use and promote good programming practice by enabling a POJO-based programming model.
The basic modules of the Spring framework are :
This is the basic Spring module, which provides the fundamental functionality
of the Spring framework. BeanFactory is the heart of any
spring-based application. Spring framework was built on the top of this module,
which makes the Spring container.
A BeanFactory is an implementation of the factory
pattern that applies Inversion of Control to separate the application’s
configuration and dependencies from the actual application code.
The most commonly used BeanFactory implementation is
the XmlBeanFactory class.
The most useful one
is org.springframework.beans.factory.xml.XmlBeanFactory, which
loads its beans based on the definitions contained in an XML file. This
container reads the configuration metadata from an XML file and uses it to
create a fully configured system or application.
The AOP module is used for developing aspects for our Spring-enabled application. Much of the support has been provided by the AOP Alliance in order to ensure the interoperability between Spring and other AOP frameworks. This module also introduces metadata programming to Spring.
With the JDBC abstraction and DAO module we can be sure that we keep up the database code clean and simple, and prevent problems that result from a failure to close database resources. It provides a layer of meaningful exceptions on top of the error messages given by several database servers. It also makes use of Spring’s AOP module to provide transaction management services for objects in a Spring application.
Spring also supports for using of an object/relational mapping (ORM) tool over straight JDBC by providing the ORM module. Spring provides support to tie into several popular ORM frameworks, including Hibernate, JDO, and iBATIS SQL Maps. Spring’s transaction management supports each of these ORM frameworks as well as JDBC.
The Spring web module is built on the application context module, providing a context that is appropriate for web-based applications. This module also contains support for several web-oriented tasks such as transparently handling multipart requests for file uploads and programmatic binding of request parameters to your business objects. It also contains integration support with Jakarta Struts.
MVC framework is provided by Spring for building web applications. Spring can easily be integrated with other MVC frameworks, butSpring’s MVC framework is a better choice, since it uses IoC to provide for a clean separation of controller logic from business objects. With Spring MVC you can declaratively bind request parameters to your business objects.
Spring configuration file is an XML file. This file contains the classes information and describes how these classes are configured and introduced to each other.
The Spring IoC is responsible for creating the objects,managing them (with dependency injection (DI)), wiring them together, configuring them, as also managing their complete lifecycle.
IOC or dependency injection minimizes the amount of code in an application. It makes easy to test applications, since no singletons or JNDI lookup mechanisms are required in unit tests. Loose coupling is promoted with minimal effort and least intrusive mechanism. IOC containers support eager instantiation and lazy loading of services.
The FileSystemXmlApplicationContext container
loads the definitions of the beans from an XML file. The full path of the XML
bean configuration file must be provided to the
constructor.
The ClassPathXmlApplicationContext container
also loads the definitions of the beans from an XML file. Here, you need to
setCLASSPATH properly because this container will look bean
configuration XML file
in CLASSPATH.
The WebXmlApplicationContext: container
loads the XML file with definitions of all beans from within a web
application.
Application contexts provide a means for resolving text messages, a generic
way to load file resources (such as images), they can publish events to beans
that are registered as listeners. In addition, operations on the container or
beans in the container, which have to be handled in a programmatic fashion with
a bean factory, can be handled declaratively in an application context. The
application context implements MessageSource, an interface
used to obtain localized messages, with the actual implementation being
pluggable.
Dependency Injection, an aspect of Inversion of Control (IoC), is a general concept, and it can be expressed in many different ways.This concept says that you do not create your objects but describe how they should be created. You don’t directly connect your components and services together in code but describe which services are needed by which components in a configuration file. A container (the IOC container) is then responsible for hooking it all up.
You can use both Constructor-based and Setter-based Dependency Injection. The best solution is using constructor arguments for mandatory dependencies and setters for optional dependencies.
The Spring
Beans are Java Objects that form the backbone of a Spring application.
They are instantiated, assembled, and managed by the Spring IoC container. These
beans are created with the configuration metadata that is supplied to the
container, for example, in the form of
XML <bean/> definitions.
Beans defined in spring framework are singleton beans. There is an attribute
in bean tag named "singleton" if specified true then bean
becomes singleton and if set to false then the bean becomes a prototype bean. By
default it is set to true. So, all the beans in spring framework are by
default singleton beans.
A Spring Bean definition contains all configuration metadata which is needed for the container to know how to create a bean, its lifecycle details and its dependencies.
There are three important methods to provide configuration metadata to the Spring Container:
When defining a <bean> in Spring, we can also
declare a scope for the bean. It can be defined through
the scope attribute in the bean definition. For example,
when Spring has to produce a new bean instance each time one is needed, the
bean’s scope attribute to beprototype. On
the other hand, when the same instance of a bean must be returned by Spring
every time it is needed, the the beanscope attribute must be
set to singleton.
There are five scoped provided by the Spring Framework supports following five scopes:
The default scope of a Spring Bean is Singleton.
No, singleton beans are not thread-safe in Spring framework.
BeanNameAware interface,
spring passes the bean’s id
to setBeanName() method.BeanFactoryAware interface,
spring passes
the beanfactory to setBeanFactory() method.BeanPostProcessors associated
with the bean, Spring
calls postProcesserBeforeInitialization()method.IntializingBean,
its afterPropertySet() method is called. If the bean
has init method declaration, the specified initialization method is
called.DisposableBean, it will call
the destroy() method.There are two important bean lifecycle methods. The first one
is setup which is called when the bean is loaded in to
the container. The second method is the teardown method
which is called when the bean is unloaded from the
container.
The bean tag has two important attributes
(init-method and destroy-method) with which
you can define your own custom initialization and destroy methods. There are
also the correspondive
annotations(@PostConstruct and @PreDestroy).
When a bean is only used as a property of another bean it can be declared as
an inner bean. Spring’s XML-based configuration metadata provides the use
of <bean/> element inside
the <property/> or <constructor-arg/> elements
of a bean definition, in order to define the so-called inner bean. Inner beans
are always anonymous and they are always scoped as prototypes.
Spring offers the following types of collection configuration elements:
<list> type is used for injecting a list
of values, in the case that duplicates are allowed.<set> type is used for wiring a set of
values but without any duplicates.<map> type is used to inject a collection
of name-value pairs where name and value can be of any type.<props> type can be used to inject a
collection of name-value pairs where the name and value are both
Strings.Wiring, or else bean wiring is the case when beans are combined together within the Spring container. When wiring beans, the Spring container needs to know what beans are needed and how the container should use dependency injection to tie them together.
The Spring container is able to autowire
relationships between collaborating beans. This means that it is
possible to automatically let Spring resolve collaborators (other beans) for a
bean by inspecting the contents of
the BeanFactory without
using <constructor-arg> and <property> elements.
The autowiring functionality has five modes which can be used to instruct Spring container to use autowiring for dependency injection:
byName,
the Spring container looks at the properties of the beans on
which autowire attribute is set
tobyName in the XML configuration file. It then tries to
match and wire its properties with the beans defined by the same names in the
configuration file.datatype, the Spring container looks at the properties of
the beans on which autowire attribute is set
to byType in the XML configuration file. It then tries
to match and wire a property if its type matches with exactly one of the beans
name in configuration file. If more than one such beans exist, a fatal
exception is thrown.byType, but type applies to constructor arguments. If
there is not exactly one bean of the constructor argument type in the
container, a fatal error is raised.byType.Limitations of autowiring are:
<constructor-arg> and <property> settings
which will always override autowiring.Yes, you can.
Java
based configuration option enables you to write most of your Spring
configuration without XML but with the help of few Java-based annotations.
An
example is the @Configuration annotation, that indicates
that the class can be used by the Spring IoC container as a source of bean
definitions. Another example is the@Bean annotated method that
will return an object that should be registered as a bean in the Spring
application context.
An alternative to XML setups is provided by annotation-based configuration which relies on the bytecode metadata for wiring up components instead of angle-bracket declarations. Instead of using XML to describe a bean wiring, the developer moves the configuration into the component class itself by using annotations on the relevant class, method, or field declaration.
Annotation wiring is not turned on in the Spring container by default. In order to use annotation based wiring we must enable it in our Spring configuration file by configuring <context:annotation-config/< element.
This annotation simply indicates that the affected bean property must be
populated at configuration time, through an explicit property value in a bean
definition or through autowiring. The container
throws BeanInitializationException if the affected bean
property has not been populated.
The @Autowired annotation provides more fine-grained
control over where and how autowiring should be accomplished. It can be used to
autowire bean on the setter method just
like @Required annotation, on the constructor, on a
property or pn methods with arbitrary names and/or multiple arguments.
When there are more than one beans of the same type and only one is needed to
be wired with a property, the @Qualifier annotation is
used along with @Autowired annotation to remove the
confusion by specifying which exact bean will be wired.
When using the Spring JDBC framework the burden of resource management and
error handling is reduced. So developers only need to write the statements and
queries to get the data to and from the database. JDBC can be used more
efficiently with the help of a template class provided by Spring framework,
which is the JdbcTemplate (example here).
JdbcTemplate class provides many convenience methods for
doing things such as converting database data into primitives or objects,
executing prepared and callable statements, and providing custom database error
handling.
The Data Access Object (DAO) support in Spring is aimed at making it easy to work with data access technologies like JDBC, Hibernate or JDO in a consistent way. This allows us to switch between the persistence technologies fairly easily and to code without worrying about catching exceptions that are specific to each technology.
There are two ways to access Hibernate with Spring:
HibernateDAOSupport and Applying an AOP
Interceptor node.Spring supports the following ORM’s:
Use
Spring’s SessionFactory called LocalSessionFactory.
The integration process is of 3 steps:
HibernateDaoSupportSpring supports two types of transaction management:
Most users of the Spring Framework choose declarative transaction management because it is the option with the least impact on application code, and hence is most consistent with the ideals of a non-invasive lightweight container. Declarative transaction management is preferable over programmatic transaction management though it is less flexible than programmatic transaction management, which allows you to control transactions through your code.
Aspect-oriented programming, or AOP, is a programming technique that allows programmers to modularize crosscutting concerns, or behavior that cuts across the typical divisions of responsibility, such as logging and transaction management.
The core construct of AOP is the aspect, which encapsulates behaviors
affecting multiple classes into reusable modules. It ia a module which has a set
of APIs providing cross-cutting requirements. For example, a logging module
would be called AOP aspect for logging. An application can have any number of
aspects depending on the requirement. In Spring AOP, aspects are implemented
using regular classes annotated with
the @Aspect annotation
(@AspectJ style).
The Concern is behavior we want to have in a module of an application. A
Concern may be defined as a functionality we want to implement.
The
cross-cutting concern is a concern which is applicable throughout the
application and it affects the entire application. For example, logging, security and
data transfer are the concerns which are needed in almost every module of an
application, hence they are cross-cutting concerns.
The join point represents a point in an application where we can plug-in an AOP aspect. It is the actual place in the application where an action will be taken using Spring AOP framework.
The advice is the actual action that will be taken either before or after the method execution. This is actual piece of code that is invoked during the program execution by the Spring AOP framework.
Spring aspects can work with five kinds of advice:
The pointcut is a set of one or more joinpoints where an advice should be executed. You can specify pointcuts using expressions or patterns.
An Introduction allows us to add new methods or attributes to existing classes.
The target object is an object being advised by one or more aspects. It will always be a proxy object. It is also referred to as the advised object.
A proxy is an object that is created after applying advice to a target object. When you think of client objects the target object and the proxy object are the same.
Weaving is the process of linking aspects with other application types or
objects to create an advised object.
Weaving can be done at compile time, at
load time, or at runtime.
In this implementation case, aspects are implemented using regular classes along with XML based configuration.
This implementation case (@AspectJ based implementation)
refers to a style of declaring aspects as regular Java classes annotated with
Java 5 annotations.
Spring comes with a full-featured MVC framework for building web applications. Although Spring can easily be integrated with other MVC frameworks, such as Struts, Spring’s MVC framework uses IoC to provide a clean separation of controller logic from business objects. It also allows to declaratively bind request parameters to business objects.
The Spring Web MVC framework is designed around
a DispatcherServlet that handles all the HTTP requests
and responses.
The WebApplicationContext is an extension of the
plain ApplicationContext that has some extra features
necessary for web applications. It differs from a
normal ApplicationContext in that it is capable of
resolving themes, and that it knows which servlet it is associated with.
Controllers provide access to the application behavior that you typically define through a service interface. Controllers interpret user input and transform it into a model that is represented to the user by the view. Spring implements a controller in a very abstract way, which enables you to create a wide variety of controllers.
The @Controller annotation indicates that a particular
class serves the role of a controller. Spring does not require you to extend any
controller base class or reference the Servlet API.
@RequestMapping annotation is used to map a URL to either
an entire class or a particular handler method.
Ok, so now you are ready for your interview! Don’t forget to check our dedicated page full of Spring Tutorials!
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reference from:http://www.javacodegeeks.com/2014/05/spring-interview-questions-and-answers.html
69 Spring Interview Questions and Answers – The ULTIMATE List--reference,布布扣,bubuko.com
69 Spring Interview Questions and Answers – The ULTIMATE List--reference
原文：http://www.cnblogs.com/davidwang456/p/3712189.html