Google Guice提供了一個名為@Singleton的注解，只要在類上加上這個注解，就可以實現一個單例類，不需要自己手動編寫單例實現類。@Named注解提供了為屬性賦值的功能。

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　　一。Scope

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Java代碼 ?

package?com.template.juice;??

??

/**?

?*?Created?by?IntelliJ?IDEA.?

?*?User:?Zhong?Gang?

?*?Date:?11-8-5?

?*?Time:?下午8:26?

?*/??

public?enum?Scope?{??

????REQUEST,??

????SESSION,??

????GLOBAL,??

????UNSCOPE??

}??

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　　二。Database

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Java代碼 ?

package?com.template.juice;??

??

import?com.google.inject.Inject;??

import?com.google.inject.Singleton;??

import?com.google.inject.name.Named;??

??

/**?

?*?Created?by?IntelliJ?IDEA.?

?*?User:?Zhong?Gang?

?*?Date:?11-8-5?

?*?Time:?下午8:33?

?*/??

@Singleton??

public?class?Database?{??

??

????@Named("driverClassName")??

????@Inject??

????private?String?driverClassName;??

??

????@Named("url")??

????@Inject??

????private?String?url;??

??

????@Named("username")??

????@Inject??

????private?String?username;??

??

????@Named("password")??

????@Inject??

????private?String?password;??

??

????/**?

?????*?Just?for?test?and?study,it?does?not?make?sense.?

?????*/??

????@Named("scope")??

????@Inject??

????private?Scope?scope;??

??

????public?String?driverClassName()?{??

????????return?driverClassName;??

????}??

??

????public?String?url()?{??

????????return?url;??

????}??

??

????public?String?username()?{??

????????return?username;??

????}??

??

????public?String?password()?{??

????????return?password;??

????}??

??

????public?Scope?scope()?{??

????????return?scope;??

????}??

}??

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　　三。DatabaseModule

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Java代碼 ?

package?com.template.juice;??

??

import?com.google.inject.AbstractModule;??

import?com.google.inject.name.Names;??

??

/**?

?*?Created?by?IntelliJ?IDEA.?

?*?User:?Zhong?Gang?

?*?Date:?11-8-5?

?*?Time:?下午8:38?

?*/??

public?class?DatabaseModule?extends?AbstractModule?{??

??

????@Override??

????protected?void?configure()?{??

??

????????bind(String.class).annotatedWith(Names.named("driverClassName")).toInstance("com.mysql.jdbc.Driver");??

??

????????bind(String.class).annotatedWith(Names.named("url")).toInstance("jdbc:mysql://localhost:3306/demo");??

??

????????bind(String.class).annotatedWith(Names.named("username")).toInstance("root");??

??

????????bind(String.class).annotatedWith(Names.named("password")).toInstance("root");??

??

????????bind(Scope.class).annotatedWith(Names.named("scope")).toInstance(Scope.GLOBAL);??

??

????}??

}??

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　　四。Main

?

Java代碼 ?

package?com.template.juice;??

??

import?com.google.inject.Guice;??

import?com.google.inject.Injector;??

import?com.google.inject.Module;??

import?org.slf4j.Logger;??

import?org.slf4j.LoggerFactory;??

??

/**?

?*?Created?by?IntelliJ?IDEA.?

?*?User:?Zhong?Gang?

?*?Date:?11-8-5?

?*?Time:?下午8:42?

?*/??

public?class?Main?{??

????private?static?Logger?logger?=?LoggerFactory.getLogger(Main.class);??

??

????public?static?void?main(String[]?args)?{??

????????Module?module?=?new?DatabaseModule();??

????????Injector?injector?=?Guice.createInjector(module);??

????????Database?instance1?=?injector.getInstance(Database.class);??

????????Database?instance2?=?injector.getInstance(Database.class);??

??

????????logger.info("driverClassName?is?"?+?instance1.driverClassName());??

????????logger.info("url?is?"?+?instance1.url());??

????????logger.info("username?is?"?+?instance1.username());??

????????logger.info("password?is?"?+?instance1.password());??

??

????????Boolean?isSingleton?=?instance1.equals(instance2);??

????????logger.info(instance1.toString());??

????????logger.info(instance2.toString());??

????????logger.info(isSingleton.toString());??

????}??

??

}??

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　　五。運行結果

　　

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　　可以看到instance1和instance2的hashcode相同，并且兩者相比為true，說明injector返回的是同一個實例。

?

　　去除Database類的@Singleton注解，運行結果為

　　

?

　　可以看到去除@Singleton注解后，instance1和instance2的hashcode不同，并且兩者相比為false，說明instance1和instance2為不同的實例。

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