Dependencies The IoC container
7.4 Dependencies
A typical enterprise application does not consist of a single object or bean in the Spring parlance. Even the simplest application has a few objects that work together to present what the end-user sees as a coherent application. This next section explains how you go from defining a number of bean definitions that stand alone to a fully realized application where objects collaborate to achieve a goal. Dependency Injection Dependency injection DI is a process whereby objects define their dependencies, that is, the other objects they work with, only through constructor arguments, arguments to a factory method, or properties that are set on the object instance after it is constructed or returned from a factory method. The container then injects those dependencies when it creates the bean. This process is fundamentally the inverse, hence the name Inversion of Control IoC, of the bean itself controlling the instantiation or location of its dependencies on its own by using direct construction of classes, or the Service Locator pattern. Code is cleaner with the DI principle and decoupling is more effective when objects are provided with their dependencies. The object does not look up its dependencies, and does not know the location or class of the dependencies. As such, your classes become easier to test, in particular when the dependencies are on interfaces or abstract base classes, which allow for stub or mock implementations to be used in unit tests. DI exists in two major variants, Constructor-based dependency injection and Setter-based dependency injection . Constructor-based dependency injection Constructor-based DI is accomplished by the container invoking a constructor with a number of arguments, each representing a dependency. Calling a static factory method with specific arguments to construct the bean is nearly equivalent, and this discussion treats arguments to a constructor and to a static factory method similarly. The following example shows a class that can only be dependency- injected with constructor injection. Notice that there is nothing special about this class, it is a POJO that has no dependencies on container specific interfaces, base classes or annotations. public class SimpleMovieLister { the SimpleMovieLister has a dependency on a MovieFinder private MovieFinder movieFinder; a constructor so that the Spring container can inject a MovieFinder public SimpleMovieListerMovieFinder movieFinder { this .movieFinder = movieFinder; } business logic that actually uses the injected MovieFinder is omitted... } Constructor argument resolution Constructor argument resolution matching occurs using the argument’s type. If no potential ambiguity exists in the constructor arguments of a bean definition, then the order in which the constructor arguments are defined in a bean definition is the order in which those arguments are supplied to the appropriate constructor when the bean is being instantiated. Consider the following class: 4.3.9.RELEASE Spring Framework 50 package x.y; public class Foo { public FooBar bar, Baz baz { ... } } No potential ambiguity exists, assuming that Bar and Baz classes are not related by inheritance. Thus the following configuration works fine, and you do not need to specify the constructor argument indexes andor types explicitly in the constructor-arg element. beans bean id = foo class = x.y.Foo constructor-arg ref = bar constructor-arg ref = baz bean bean id = bar class = x.y.Bar bean id = baz class =x.y.Baz beans
Parts
» Dependency Injection and Inversion of Control Framework Modules
» Usage scenarios Introduction to the Spring Framework
» Java EE 6 and 7 Groovy Bean Definition DSL
» Core Container Improvements General Web Improvements
» WebSocket, SockJS, and STOMP Messaging Testing Improvements
» JMS Improvements Caching Improvements
» Web Improvements New Features and Enhancements in Spring Framework 1
» WebSocket Messaging Improvements Testing Improvements
» Core Container Improvements New Features and Enhancements in Spring Framework 4.2
» Data Access Improvements JMS Improvements Web Improvements
» Core Container Improvements Data Access Improvements Caching Improvements
» JMS Improvements Web Improvements WebSocket Messaging Improvements Testing Improvements
» Introduction to the Spring IoC container and beans
» Container overview The IoC container
» Bean overview The IoC container
» Dependencies The IoC container
» y.Baz beans The IoC container
» driverClassName = username = The IoC container
» email = spouse-ref = The IoC container
» y.Bar bean y.Foo constructor-arg y.Foo c:bar-ref baz-ref = y.Foo c:_0-ref _1-ref =
» y.z.MyValueCalculator b.c.ReplacementComputeValue Bean scopes
» y.Foo property Customizing the nature of a bean
» Bean definition inheritance The IoC container
» Container Extension Points The IoC container
» Annotation-based container configuration The IoC container
» Classpath scanning and managed components
» Using JSR 330 Standard Annotations
» Java-based container configuration The IoC container
» Environment abstraction The IoC container
» Registering a LoadTimeWeaver Additional Capabilities of the ApplicationContext
» The BeanFactory The IoC container
» Introduction The Resource interface
» Built-in Resource implementations Resources
» The ResourceLoaderAware interface Resources
» Resources as dependencies Application contexts and Resource paths
» Introduction Validation, Data Binding, and Type Conversion
» Validation using Spring’s Validator interface
» Resolving codes to error messages Bean manipulation and the BeanWrapper
» Spring Type Conversion Validation, Data Binding, and Type Conversion
» Spring Field Formatting Validation, Data Binding, and Type Conversion
» Configuring a global date time format
» Spring Validation Validation, Data Binding, and Type Conversion
» Introduction Feature Overview Spring Expression Language SpEL
» Expression Evaluation using Spring’s Expression Interface
» Expression support for defining bean definitions
» Language Reference Spring Expression Language SpEL
» 3e0 4 .getValueDouble. 4e0 2 .getValueDouble.
» Classes used in the examples
» Introduction Aspect Oriented Programming with Spring
» Schema-based AOP support Aspect Oriented Programming with Spring
» y.service.DefaultFooService y.SimpleProfiler aop:config
» Choosing which AOP declaration style to use
» Mixing aspect types Proxying mechanisms
» Introduction Pointcut API in Spring
» Advisor API in Spring Using the ProxyFactoryBean to create AOP proxies
» Concise proxy definitions Spring AOP APIs
» Creating AOP proxies programmatically with the ProxyFactory Manipulating advised objects
» Using the auto-proxy facility
» Using TargetSources Spring AOP APIs
» Mock Objects Unit Testing support Classes
» Overview Goals of Integration Testing
» JDBC Testing Support Annotations
» Spring TestContext Framework Integration Testing
» loginAction-ref = username = userPreferences-ref = theme =
» PetClinic Example Integration Testing
» Understanding the Spring Framework transaction abstraction
» Synchronizing resources with transactions
» Declarative transaction management Transaction Management
» y.service.DefaultFooService Transaction Management
» y.service.DefaultFooService y.SimpleProfiler y.service.DefaultFooService
» y.SimpleProfiler Transaction Management
» Programmatic transaction management Transaction Management
» Choosing between programmatic and declarative transaction management Transaction bound event
» Application server-specific integration Transaction Management
» Introduction Consistent exception hierarchy
» Annotations used for configuring DAO or Repository classes
» Introduction to Spring Framework JDBC
» Using the JDBC core classes to control basic JDBC processing and error handling
» Controlling database connections Data access with JDBC
» JDBC batch operations Data access with JDBC
» Simplifying JDBC operations with the SimpleJdbc classes
» Modeling JDBC operations as Java objects
» Common problems with parameter and data value handling
» Embedded database support Data access with JDBC
» Initializing a DataSource Data access with JDBC
» Introduction to ORM with Spring
» General ORM integration considerations
» Hibernate Object Relational Mapping ORM Data Access
» JDO Object Relational Mapping ORM Data Access
» Introduction Marshaller and Unmarshaller
» Using Marshaller and Unmarshaller
» XML Schema-based Configuration JAXB
» Castor Marshalling XML using OX Mappers
» XMLBeans JiBX Marshalling XML using OX Mappers
» XStream Marshalling XML using OX Mappers
» Introduction to Spring Web MVC framework
» The DispatcherServlet Web MVC framework
» Handler mappings Web MVC framework
» Resolving views Web MVC framework
» Using flash attributes Web MVC framework
» Building URIs Web MVC framework
» Using locales Web MVC framework
» Using themes Web MVC framework
» Spring’s multipart file upload support
» Handling exceptions Web MVC framework
» Web Security Convention over configuration support
» y.RegistrationController HTTP caching support
» Code-based Servlet container initialization
» Configuring Spring MVC Web MVC framework
» simpleDateFormat = Web MVC framework
» Introduction Thymeleaf Groovy Markup Templates
» Velocity FreeMarker View technologies
» Document views PDFExcel Property
» Feed Views JSON Mapping View
» Introduction Integrating with other web frameworks
» Common configuration Integrating with other web frameworks
» JavaServer Faces 1.2 Apache Struts 2.x
» Introduction Portlet MVC Framework
» The DispatcherPortlet Portlet MVC Framework
» The ViewRendererServlet Controllers Portlet MVC Framework
» Handler mappings Portlet MVC Framework
» Views and resolving them Multipart file upload support
» Handling exceptions Annotation-based controller configuration
» absolute-ordering absolute-ordering WebSocket API
» SockJS Fallback Options WebSocket Support
» STOMP Over WebSocket Messaging Architecture
» Introduction Controller method CORS configuration
» Global CORS configuration Advanced Customization
» Introduction Remoting and web services using Spring
» Using Hessian or Burlap to remotely call services via HTTP
» Exposing services using HTTP invokers
» Web services Remoting and web services using Spring
» JMS Remoting and web services using Spring
» Accessing RESTful services on the Client
» Introduction Accessing EJBs Enterprise JavaBeans EJB integration
» Introduction JMS Java Message Service
» Using Spring JMS JMS Java Message Service
» Sending a Message JMS Java Message Service
» Receiving a message JMS Java Message Service
» Support for JCA Message Endpoints
» Annotation-driven listener endpoints JMS Java Message Service
» JMS namespace support JMS Java Message Service
» Introduction Exporting your beans to JMX
» Controlling the management interface of your beans
» Controlling the ObjectNames for your beans
» Accessing MBeans via Proxies
» Introduction Configuring CCI JCA CCI
» Using Spring’s CCI access support
» Modeling CCI access as operation objects
» Using the JavaMail MimeMessageHelper
» Introduction The Spring TaskExecutor abstraction
» The Spring TaskScheduler abstraction
» Annotation Support for Scheduling and Asynchronous Execution
» The task namespace Task Execution and Scheduling
» Introduction A first example
» y.DefaultBookingService property Defining beans that are backed by dynamic languages
» y.DefaultBookingService property Dynamic language support
» Scenarios Dynamic language support
» Bits and bobs y.DefaultBookingService property
» Introduction Understanding the cache abstraction
» Declarative annotation-based caching Cache Abstraction
» JCache JSR-107 annotations Cache Abstraction
» Declarative XML-based caching y.service.DefaultBookService
» Configuring the cache storage name =
» Classic ORM usage Classic Spring Usage
» JMS Usage Classic Spring Usage
» Concise proxy definitions Classic Spring AOP Usage
» Using the autoproxy facility
» Using TargetSources Classic Spring AOP Usage
» Introduction XML Schema-based configuration
» Introduction Authoring the schema
» Coding a NamespaceHandler Extensible XML authoring
» BeanDefinitionParser Extensible XML authoring
» Registering the handler and the schema
» Using a custom extension in your Spring XML configuration Meatier examples
» Introduction The argument tag The bind tag
» The escapeBody tag The eval tag The hasBindErrors tag
» The htmlEscape tag The message tag
» The nestedPath tag The param tag The theme tag
» The transform tag The url tag
» Introduction The button tag The checkbox tag
» The checkboxes tag The errors tag
» The option tag The options tag
» The password tag The radiobutton tag
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