5  The IoC container

When the context is refreshed , that callback will be invoked, and at that point the default lifecycle processor will check the boolean value returned by each SmartLifecycle object’sisAutoStartup() method. If “true”, then that object will be started at that point rather than waiting for an explicit invocation of the context’s or its own start() method . The “phase” value as well as any “depends-on” relationships will determine the startup order in the same way as described above.

Consult the Javadoc for theBeanFactoryPostProcessor andOrdered interfaces for more details. Are instantiated on startup, as part of the special startup phase of theApplicationContext.

Configuration Class

Some explanations go to such a low level that the big picture is missed, whereas others are too vague. Also, while it’s easy enough to debug these issues locally when developing the application, we’re talking about production here – we can’t afford the downtime while you’re stepping in and out of code. For each round of the race we would need to instantiate a RaceTrack and a Driver, so we would use the new keyword to handle those instantiations.

It uses these beans as bean factory post-processors, at the appropriate time. You can deploy these post-processor beans as you would any other bean. You can configure multipleBeanFactoryPostProcessors, and you can control the order in which these BeanFactoryPostProcessors execute by setting the order property. However, you can only set this property if theBeanFactoryPostProcessor implements theOrdered interface. If you write your ownBeanFactoryPostProcessor, you should consider implementing the Ordered interface too.

14.5 Deploying a Spring ApplicationContext as a J2EE RAR file

A bean definition can contain a lot of configuration information, including constructor arguments, property values, and container-specific information such as initialization method, static factory method name, and so on. A child bean definition inherits configuration data from a parent definition. The child definition can override some values, or add others, as needed. Objects created by the container are also called managed objects or beans. The container can be configured by loading XML files or detecting specific Java annotations on configuration classes. These data sources contain the bean definitions which provide the information required to create the beans. A child bean definition inherits scope, constructor argument values, property values, and method overrides from the parent, with the option to add new values.

Thus autowiring can be especially useful during development, without negating the option of switching to explicit wiring when the code base becomes more stable. Lazy-initialized, theApplicationContext creates the lazy-initialized bean at startup, because it must satisfy the singleton’s dependencies.

3.1 Naming beans

In Spring, the objects that form the backbone of your application and that are managed by the Spring IoC container are called beans. A bean is an object that is instantiated, assembled, and otherwise managed by a Spring IoC container. Otherwise, a bean is simply one of many objects in your application. Beans, and the dependencies among them, are reflected in the configuration metadata used by a container. But we do not want to use the @Component and @ComponentScan annotations to create the beans. So we are going to create the spring beans using the @Bean annotation. To create the College class bean using the @Bean annotation inside the configuration class we can write something like this inside our CollegeConfig.java file.

The object should be returned, but you can return null if the object with the specified name is not found. The session scope implementation, for example, returns the session-scoped bean . If you write a standard Servlet-based web application and you define one or more beans as having global session scope, the standard HTTP Session scope is used, and no error is raised. Scopes a single bean definition to the lifecycle of a global HTTP Session. Scopes a single bean definition to the lifecycle of an HTTP Session. A less useful form of method injection than lookup method Injection is the ability to replace arbitrary methods in a managed bean with another method implementation.

Setter Dependency Injection

Spring have the IoC container which carry the Bag of Bean ; creation maintain and deletion are the responsibilities of Spring Container. Such classes are considered as candidates for auto-detection when using annotation-based configuration and class path scanning. Now to check our application let’s create a main method inside our Main class. Comments are added inside the code to understand the code in more detail. When we define classes, we give them a particular name, such as RaceRound. When the container instantiates a bean from this class it populates the class property of that bean with the fully qualified name we have provided.

• Now to check our application let’s create a main method inside our Main class.
• Doing so achieves a “Java-centric” approach to configuring the container and keeps XML to a bare minimum.
• Unfortunately, there aren’t clear answers to the simple question of what a Spring bean really is.
• In order for this to work, thefred property of foo, and thebob property of fred must not benull after the bean is constructed, or aNullPointerException is thrown.
• The session scope implementation, for example, returns the session-scoped bean .
• The BeanFactory interface provides an advanced configuration mechanism capable of managing any type of object.ApplicationContext is a sub-interface ofBeanFactory.
• The FactoryBean interface is a point of pluggability into the Spring IoC container’s instantiation logic.
• In these scenarios, simply use @ImportResource and define only as much XML as is needed.

The container injects this proxy object into theuserManager bean, which is unaware that thisUserPreferences reference is a proxy. In this example, when a UserManager instance invokes a method on the dependency-injectedUserPreferences object, it actually is invoking a method on the proxy. The proxy then fetches the realUserPreferences object from the HTTP Session, and delegates the method invocation onto the retrieved realUserPreferences object. For creating actual instances of the class defined by that bean definition. The idea that a bean definition is a recipe is important, because it means that, as with a class, you can create many object instances from a single recipe. The lookup typically involves a prototype bean as in the scenario described in the preceding section. The Spring Framework implements this method injection by using bytecode generation from the CGLIB library to generate dynamically a subclass that overrides the method.

5.3 Singleton beans with prototype-bean dependencies

These types must be ‘wired up’ explicitly via XML or using a Spring@Bean method. Constructor whose dependencies can be satisfied, that is the constructor that has the largest number of arguments. XML injection, thus the latter configuration will override the former for properties wired through both approaches. When you need to ask a container for an actualFactoryBean instance itself instead of the bean it produces, preface the bean’s id with the ampersand symbol (&) when calling thegetBean() method of theApplicationContext. So for a givenFactoryBean with an id ofmyBean, invoking getBean(“myBean”)on the container returns the product of theFactoryBean; whereas, invokinggetBean(“&myBean”) returns theFactoryBean instance itself. Compound property names are also supported, as long as every component of the path except the final property being overridden is already non-null . Notice that the LifecycleProcessor is itself an extension of the Lifecycleinterface.