Spring Framework Application Series II: Component-scan Automatic Scan Registration assembly

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Solve the problem

The business logic Bean is registered into the spring container through Component-scan automatic scanning, and the XML configuration file bean is removed from the manual registration process, which reduces the complexity of XML configuration file.

Content Description

1. When registering a scan bean and using @autowired annotations to assemble automatically, you need to introduce <context:component-scan base-package= in the XML configuration file " Com.spring.example.scan "/>;

2, through the Component-scan automatic scanning definition base class package All beans, need to add the annotation @component before the class name, and can customize the bean id< @Component ("Instru"); The ID of the righteous bean is the default class name (all lowercase), and the scanned bean is loaded into the spring container;

3, after the spring container is started (get to the Spring container instance), through the autowired annotations and the Bean ID (Qualifier) to assemble and inject the corresponding instance object;

4, call the instance method;

Application Example (package name: Com.spring.example.scan)

The spring configuration file Component-scan.xml is as follows

<?XML version= "1.0" encoding= "UTF-8"?><Beansxmlns= "Http://www.springframework.org/schema/beans"Xmlns:xsi= "Http://www.w3.org/2001/XMLSchema-instance"Xmlns:context= "Http://www.springframework.org/schema/context"xsi:schemalocation= "Http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd Http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd " >    <!--automatically scans the bean and defines the bean, and puts the bean into the spring container -    <Context:component-scanBase-package= "Com.spring.example.scan"/>    </Beans>

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Instrument Interface Code

 Public Interface Instrument {    void  play ();}

Guitar Implementing Interface Instrument code

@Component  Public class Implements Instrument {    @Override    publicvoid  play () {        System.out.println ("Guitar ....");}    }

Performer Interface Code

 Public Interface Performer {    void  perform ();}

Instrumentalist implementing interface Performer code

@Component ("Instru")//Specify Bean ID Public classInstrumentalistImplementsPerformer { Publicinstrumentalist () {} @Value ("Yesterday Once more!")    PrivateString Song; //@Autowired can assemble properties, methods, constructors, as long as the types are the same (this is the instrument type)//limit ambiguity dependence, use @autowired annotations to assemble automatically, satisfy the multiple bean of assembly ,//you can narrow the scope by specifying @qualifier.@Autowired @Qualifier ("Guitar")//specifying beans by ID    Privateinstrument instrument;  Public voidSetsong (String song) { This. Song =Song; }     Public voidSetinstrument (instrument instrument) { This. Instrument =instrument; } @Override Public voidperform () {System.out.println ("Playing" + Song + ":");    Instrument.play (); }}

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Test code

 Public classDriverextendsApplication { Public Static voidMain (string[] args) {launch (args); } @Override Public voidStart (Stage primarystage) {Try{ApplicationContext CTX=NewClasspathxmlapplicationcontext ("Spring/component-scan.xml"); Performer Performer= (performer) Ctx.getbean ("Instru");        Performer.perform (); }Catch(Exception e) {e.printstacktrace (); }    }}

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Summary      

Component-scan automatic scanning advantages and disadvantages:

Advantages: a> Component-scan Automatic Scanning registration assembly can effectively solve the shortcomings of annotation-config, do not need to specify the bean in the spring configuration file, so that the configuration file is very concise;

B> removes the process of defining beans in XML, assembling and injecting directly into the application, reducing the errors caused by changing class Mingshi;

Disadvantage: The third-party interface instance Bean cannot be obtained automatically;

Application Scenarios

applicable to the development of their own business logic;

This article describes may have the wrong or not the whole place, welcome everybody to spit the trough!

Spring Framework Application Series II: Component-scan Automatic Scan Registration assembly