006-spring Boot Auto Configuration

First, interface condition, Conditional (principle)

Mainly provide methods

Boolean matches (conditioncontext context, annotatedtypemetadata metadata);

True: Indicates assembly

False: Indicates no assembly

Note: the Conditional () parameter is an array, and the array is true before assembling

@Target ({elementtype.type, elementtype.method}) @Retention (retentionpolicy.runtime) @Documented  public @Interface  Conditional {    /**     * All {@link  Condition}s that must {@linkplain  condition#matches Match} * On order for the component to be     re gistered.      */     Classextends condition>[] Value ();

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Usually used in conjunction with.

Example:

Interface: Encodingconvert

 Package Com.lhx.spring.springboot_auto_config;  Public Interface Encodingconvert {}

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Interface implementation one: Utf8encodingconvert

 Package Com.lhx.spring.springboot_auto_config;  Public class Implements Encodingconvert {}

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Interface implementation two: Gbkencodingconvert

 Package Com.lhx.spring.springboot_auto_config;  Public class Implements Encodingconvert {}

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Configuration class:

 PackageCom.lhx.spring.springboot_auto_config;Importorg.springframework.boot.SpringBootConfiguration;ImportOrg.springframework.context.annotation.Bean;Importorg.springframework.context.annotation.Conditional; @SpringBootConfiguration Public classencodingconvertconfiguration {@Bean PublicEncodingconvert Creategbkencodingconvert () {return NewGbkencodingconvert (); } @Bean PublicEncodingconvert Createutf8encodingconvert () {return NewUtf8encodingconvert (); }}

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APP:

 PackageCom.lhx.spring.springboot_auto_config;Importorg.springframework.boot.SpringApplication;Importorg.springframework.boot.autoconfigure.SpringBootApplication;ImportOrg.springframework.context.ConfigurableApplicationContext;ImportOrg.springframework.context.annotation.Bean;Importorg.springframework.context.annotation.Condition;Importorg.springframework.context.annotation.Conditional; @SpringBootApplication Public classApp {@Bean PublicRunnable createrunnable () {return(){System.out.println ("Spring Boot is running");    }; }     Public Static voidMain (string[] args) {Configurableapplicationcontext context= Springapplication.run (App.class, args); Context.getbean (Runnable.class). Run (); //You can modify the-DFILE.ENCODING=GBK with the start parameterSystem.out.println (System.getproperty ("file.encoding")); System.out.println (Context.getbeansoftype (Encodingconvert.class));    Context.close (); }}

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At this point, you will find that even an interface implementation will be assembled.

Utf8condition Implementing the Condition interface

 PackageCom.lhx.spring.springboot_auto_config;Importorg.springframework.context.annotation.Condition;ImportOrg.springframework.context.annotation.ConditionContext;ImportOrg.springframework.core.type.AnnotatedTypeMetadata; Public classUtf8conditionImplementsCondition {@Override Public Booleanmatches (conditioncontext context, Annotatedtypemetadata metadata) {String encoding= System.getproperty ("file.encoding"); if(Encoding! =NULL) {            return"Utf-8". Equalsignorecase (encoding); }        return false; }}

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Gbkcondition Implementing the Condition interface

 PackageCom.lhx.spring.springboot_auto_config;Importorg.springframework.context.annotation.Condition;ImportOrg.springframework.context.annotation.ConditionContext;ImportOrg.springframework.core.type.AnnotatedTypeMetadata; Public classGbkconditionImplementsCondition {@Override Public Booleanmatches (conditioncontext context, Annotatedtypemetadata metadata) {String encoding= System.getproperty ("file.encoding"); if(Encoding! =NULL) {            return"GBK". Equalsignorecase (encoding); }        return false; }}

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Modifying the Configuration Class

 PackageCom.lhx.spring.springboot_auto_config;Importorg.springframework.boot.SpringBootConfiguration;ImportOrg.springframework.context.annotation.Bean;Importorg.springframework.context.annotation.Conditional; @SpringBootConfiguration Public classencodingconvertconfiguration {@Bean @Conditional (gbkcondition.class)     PublicEncodingconvert Creategbkencodingconvert () {return NewGbkencodingconvert (); } @Bean @Conditional (utf8condition.class)     PublicEncodingconvert Createutf8encodingconvert () {return NewUtf8encodingconvert (); }}

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At this point, you will find that the interface class is assembled according to the file.encoding value.

Can be increased at startup parameters

-dfile.encoding=gbk

　　

Then debug and find the Assembly class has changed.

Note: @Conditional can also function on a class

Second, Spring provides the conditional automatic configuration

Jar:spring-boot-autoconfigure, org.springframework.boot.autoconfigure.condition; that is, Spring-boot provides

Conditionalonbean: Assembled when a bean is present

Conditionalonmissingbean: Assembly When a bean is not present

Conditionalonclass: When Classpath is assembled

Conditionalonexpression:

CONDITIONALONJAVA:JDK version meets time to assemble

Conditionalonnotwebapplication: Not a Web environment to assemble
Conditionalonwebapplication: It's a web environment to assemble

Conditionalonresource: The resource exists before assembling

Conditionalonproperty: Configuration exists before Assembly

Example one: Conditionalonproperty configuration is configured when there is a match

Add Configuration Class

 PackageCom.lhx.spring.springboot_auto_config;Importorg.springframework.boot.SpringBootConfiguration;ImportOrg.springframework.boot.autoconfigure.condition.ConditionalOnProperty;ImportOrg.springframework.context.annotation.Bean; @SpringBootConfiguration Public classuserconfiguration {@Bean @ConditionalOnProperty (name= "Runnable.enable", Havingvalue = "true")     PublicRunnable createrunnable () {return() {        }; }}

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APP2 Writing

 PackageCom.lhx.spring.springboot_auto_config;Importorg.springframework.boot.SpringApplication;Importorg.springframework.boot.autoconfigure.SpringBootApplication;ImportOrg.springframework.context.ConfigurableApplicationContext;ImportOrg.springframework.context.annotation.Bean;Importorg.springframework.context.annotation.Condition;Importorg.springframework.context.annotation.Conditional; @SpringBootApplication Public classAPP2 { Public Static voidMain (string[] args) {Configurableapplicationcontext context= Springapplication.run (App2.class, args); System.out.println (Context.getbeansoftype (Runnable.class));    Context.close (); }}

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The default is no assembly.

Can be assembled by adding runnable.enable=true in Application.properties

or @conditionalonproperty (name = "Runnable.enable", Havingvalue = "true") increase

Matchifmissing=true, indicating that the configuration does not take effect when

Example two: Conditionalonclass Classpath has a class to assemble

Add or remove Maven to see the effect

        <Dependency>            <groupId>Com.google.code.gson</groupId>            <Artifactid>Gson</Artifactid>            <version>2.8.2</version>        </Dependency>

Using code

    @Bean    @ConditionalOnClass (name= "Com.google.gson.Gson")    public  Runnable creategsonrunnable () {        return () {        };    }

Example three, Conditionalonbean: assembly based on whether a bean exists in the container

    @Bean    @ConditionalOnBean (name= "User")    public  Runnable Createonbeanrunnable () {        return () {        };    }

006-spring Boot Auto Configuration