Spring-condition settings

In order to produce a more suitable bean under different conditions, you can configure its condition using condition. If there is a bean,id for Magicbean, it is generated only if it has a magic attribute, as follows:

Javaconfig mode: Just add @conditional where you want to declare the bean

1  PackageCom.myapp;2 3 ImportOrg.springframework.context.annotation.Bean;4 Importorg.springframework.context.annotation.Conditional;5 6  Public classMagicbean {7@Bean//explicitly declares a bean,id default to the method name8@Conditional (magicexistsconditional.class)//generates the bean's condition judgment, the parameter type is class, accepts the return Boolean value, is true to generate the bean otherwise does not generate9      PublicMagicbean Magicbean () {Ten         return NewMagicbean (); One     } A}

How is the parameter (magicexistsconditional.class) written?

1  PackageCom.myapp;2 3 Importorg.springframework.context.annotation.Condition;4 ImportOrg.springframework.context.annotation.ConditionContext;5 Importorg.springframework.core.env.Environment;6 ImportOrg.springframework.core.type.AnnotatedTypeMetadata;7 8  Public classMagicexistsconditionalImplementscondition{9 Ten @Override One      Public Booleanmatches (Conditioncontext arg0, Annotatedtypemetadata arg1) { A         //TODO auto-generated Method Stub -Environment Env=arg0.getenvironment ();//Get Context Environment -         returnEnv.containsproperty ("Magic");//Check if the Magic attribute is included the     } -  -}

This is done only by Conditioncontext type of arg0 to get the environment type of env, through the env call method to determine whether there is a magic attribute.

and Conditioncontext and Annotatedtypemetadata are interfaces, which define a number of methods, see "Spring Combat (4th edition)" p75-p78.

Spring-condition settings