Spring 3. Three bean configuration methods in X are explained in detail

In the past, the Java framework basically used XML as the configuration file, but now the Java framework supports "zero configuration" based on annotation to replace the XML configuration file. Struts 2, hibernate and spring all began to use annotation to replace the XML configuration file; In spring 3 X provides three options: XML based configuration, annotation based configuration, and Java class based configuration.

The following describes the three configuration modes respectively; First, define a JavaBean for example.

1、 XML based configuration

In XML configuration, beans are defined through < bean > < / bean >, and the name of the bean is defined through the ID or name attribute. If the ID and name attributes are not specified, spring will automatically take the fully qualified class name as the name of the bean. Inject values into the bean through the < property > child element or the dynamic properties of the P namespace. You can also set the life process method by specifying the method name of the bean implementation class through the init method and destruction method properties of < bean > (specify at most one initialization method and destruction method). You can specify the scope of the bean through the scope of < bean >. You have heard that the lazy init property of < bean > specifies whether to delay initialization.

When the implementation class of bean comes from a third-party class library, such as datasource and hibernatetemplate, annotation information cannot be marked in the class and can only be configured through XML; Moreover, the configuration of namespaces, such as AOP and context, can only be XML based.

2、 Annotation based configuration

In the bean implementation class, annotate the bean class through some annotations:

・ @ component: mark a common springbean class (bean name can be specified. If not specified, the class name starting with lowercase letter will be used by default)

・ @ controller: label a controller class

・ @ service: mark a business logic class

・ @ Repository: label a Dao class

You can also use @ qualifier to configure injection by name by labeling @ Autowired at the member variable or method input parameter to match injection by type. The initialization method and destruction method specified by @ postconstruct and predestroy annotations on the method (any number can be defined). The scope of the bean is specified by @ scope ("prototype"). Specify the deferred loading of the bean by labeling @ lazy (true) at the class definition.

When the bean implementation class is developed by the current project, you can directly use annotation based configuration in Java classes, which is relatively simple.

3、 Java based class configuration

In the Java class labeled @ configuration, define a bean by labeling @ bean in the class method. Method must provide the instantiation logic of the bean. The name of the @ bean can be defined through its name attribute. If not specified, the default name is the method name. Bind the method input parameter to the bean through @ Autowired at the method, and then inject it through code in the method; You can also call the @ bean method of the configuration class for injection. Specify an initialization or destruction method through the initmethod or destroymethod of @ bean. Specify the scope of the bean through the annotation @ scope at the bean method definition. Specify the delayed initialization of the bean by labeling @ lazy at the bean method definition.

When the logic of instantiating beans is complex, it is more suitable for Java class configuration.

summary

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