Spring basic knowledge of assembly bean

Assembly (Wiring): Creates the behavior of collaborative relationships between application objects. This is the essence of dependency injection.

Optional Scenarios for spring configuration

Spring offers three kinds of assembly wit:

1) display assembly in XML

2) display assembly in Java

3) Implicit bean discovery Mechanism and auto-assembly

Automated assembly

Spring implements automated assembly from two angles:

1) Component Scan (component scanning): Spring automatically discovers the bean that is created in the app context.

2) automatic assembly (autowiring): Spring automatically satisfies the dependencies between beans.

Create a bean that can be discovered 　　

Case: Use CD and CD player to realize why there is injection and dependency.

CD: As an interface, defines a series of CD player operations on the CD, while minimizing the coupling of the CD player to the CD itself

 Public Interface Compactdisc {    void  play ();}

The specific implementation of the CD:

Note: @Component. This annotation indicates that the class will act as a component class and tell spring to create a bean for this class.

@Component  Public class Implements Compactdisc {    private String title = "Sgt. Pepper ' s Lonely Hearts Club Band ";     Private String artist = "The Beatles";      Public void Play () {        System.out.println ("Playing" + title + "by  " + artist);}    }

To configure the component scan class:

Note: @ComponentScan, the note will default to scan all classes with @component under the package of the configuration class and its sub-packages

Use the:<context:component-scan> element if you use XML format

@ComponentScan @configuration  Public class Cdplayerconfig {}

Test Class Code:

Note: @ContextConfiguration will tell it to load the configuration in Cdplayerconfig, and Cdplayerconfig contains the annotation @componentscan, All the @component class scans under its package and its sub-packages, and generates beans for it

@ContextConfiguration (classes = cdplayerconfig.  Class)publicclass  cdplayertest {    @Autowired    Private Compactdisc Compactdisc;    @Test    publicvoid  Test () {        compactdisc.play ();    }}

Name The bean scanned by the component

All beans in the Spring app context will be given an ID. The default is the lowercase class name.

To change this ID: Just modify the annotations to

@Component ("Myselfbean")publicclassimplements  Compactdisc {... }

set up the base package for component scanning

We do not currently have any properties set for @componentscan, and the component is scanned by default in the package that contains the configuration class.

You can scan the package name with the following settings:

@Configuration @componentscan ("com")  Public class Cdplayerconfig {}

If you want to specify the base package:

= "com")publicclass  cdplayerconfig {}

You can also scan multiple base packages:

= {"com", "cn"})publicclass  cdplayerconfig {}

Also provides another way to designate a class or interface that is contained in a package:

Note: You can create a component class specifically for scanning in packages that you must scan.

= {Cdplayerconfig. class, Test.class})publicclass  cdplayerconfig {}

automate Assembly by adding annotations to beans

Automatic assembly: Spring automatically satisfies bean dependencies in one way. Automatic assembly can be achieved with @autowired.

@Component  Public class Implements mediaplayer{    @Autowired    private  compactdisc compactdisc;      Public void Play () {        compactdisc.play ();    }}

assembling beans through Java codeCreate a configuration class

Note: @Configuration indicates that the class is a configuration class that should contain details of how the bean is created in the spring application context.

@Configuration  Public class Cdplayerconfig {}

declaring a simple bean

Note: @Bean will tell Spring that the object returned is the bean for the spring application context. The Name property of the @Bean can be set by default and the name is the same as the method name.

@Configuration  Public class cdplayerconfig {    @Bean    public  compactdisc getcompactdisc () {        return  New  sgtpeppers ();    }}

The XML format is not a record

Spring basic knowledge of assembly bean