【Hello】Guice

介绍
Guice is a lightweight dependency injection framework for Java .
即 Guice 是轻量级依赖注入的 Java 框架。

Guice

特点

1. 取消 Bean 概念，使用 Java 代码描述绑定规则
2. 泛型支持
3. 专注于 Dependency Injection

依赖

Maven

<!-- Guice -->
<dependency>
    <groupId>com.google.inject</groupId>
    <artifactId>guice</artifactId>
    <version>4.2.1</version>
</dependency>

<!-- Guice扩展插件：多值绑定 -->
<dependency>
    <groupId>com.google.inject.extensions</groupId>
    <artifactId>guice-multibindings</artifactId>
    <version>4.2.1</version>
</dependency>

Gradle

// Guice
compile 'com.google.inject:guice:4.2.1'

// Guice扩展插件：多值绑定
compile 'com.google.inject.extensions:guice-multibindings:4.2.1'

注入 @Inject

1.构造器注入（推荐）

public class BookManager {

    private final BookService bookService;
    private final PriceService priceService;

    @Inject
    public BookManager(BookService bookService, PriceService priceService) {
        this.bookService = bookService;
        this.priceService = priceService;
    }
    ...
}

2.设值注入

public class BookManager {

    @Inject
    private BookService bookService;

    @Inject
    private PriceService priceService;
    ...
}

绑定 bind(…)

1.类名绑定

bind(BookService.class).to(BookServiceImpl.class);

2.实例绑定

bind(BookDao.class).toInstance(new BookDaoImpl()));

3.链式绑定

bind(PriceService.class).to(PriceServiceImpl.class);
bind(PriceServiceImpl.class).toInstance(new PriceServiceImpl() {
    @Override
    public BigDecimal getPrice() {
        return BigDecimal.ONE;
    }
});

4.Provider 绑定

bind(CurrencyService.class).toProvider(CurrencyProvider.class);

@Provides
List<String> getSupportedCurrencies(CurrencyService currencyService) {
    return currencyService.getSupportedCurrency();
}

5.命名绑定

@Provides
@Named("supportedCurrencies")
List<String> getSupportedCurrencies(CurrencyService currencyService) {
    return currencyService.getSupportedCurrency();
}

6.泛型绑定

bind(new TypeLiteral<List<String>>() {})
        .annotatedWith(Names.named("supportedCurrencies"))
        .toInstance(Arrays.asList("CNY", "JPY"));

7.集合绑定

// 集合Set绑定
Multibinder<String> currencyBinder = Multibinder.newSetBinder(binder(), String.class);
currencyBinder.addBinding().toInstance("ZH");
currencyBinder.addBinding().toInstance("EN");
currencyBinder.addBinding().toInstance("DE");

// 集合Map绑定
MapBinder<String, Integer> authorBinder = MapBinder.newMapBinder(binder(),String.class,Integer.class);
authorBinder.addBinding("Leif").toInstance(20);
authorBinder.addBinding("Chen").toInstance(18);

Module 的相互关系

1. 并列
2. 嵌套
3. 覆盖

作用域

1. 默认：一般实例，构造速度快
2. 单例 singleton ：构造速度慢的实例，必须线程安全，如数据库连接
3. Session Scope ：含有 session/request 信息的实例

Guice 与 Spring 的依赖注入代码比较

一、Spring 依赖注入

• Dao

public interface UserDao {

    void save();
}

public class UserDaoImpl implements UserDao {

    @Override
    public void save() {
        System.out.println("Spring BookDao method: save().");
    }
}

• Service

public interface UserService {

    void save();
}

public class UserServiceImpl implements UserService {

    private final UserDao userDao;

    public UserServiceImpl(UserDao userDao) {
        this.userDao = userDao;
    }

    @Override
    public void save() {
        System.out.println("Spring BookService method: save().");
        userDao.save();
    }
}

• Manager

public class UserManager {

    private final UserService userService;

    public UserManager(UserService userService) {
        this.userService = userService;
    }

    public void test() {
        userService.save();
    }
}

• 配置文件 applicationContext.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean id="userDao" class="com.chen.spring.dao.impl.UserDaoImpl"/>
    <bean id="userService" class="com.chen.spring.service.impl.UserServiceImpl">
        <constructor-arg ref="userDao"/>
    </bean>
    <bean id="userManager" class="com.chen.spring.manager.UserManager">
        <constructor-arg ref="userService"/>
    </bean>

</beans>

• 主程序

public class SpringApp {

    public static void main(String[] args) {
        BeanFactory beanFactory = new ClassPathXmlApplicationContext("applicationContext.xml");
        UserManager userManager = (UserManager) beanFactory.getBean("userManager");
        userManager.test();
    }
}

二、Guice 依赖注入

• Dao

public interface BookDao {

    void save();
}

public class BookDaoImpl implements BookDao {

    @Override
    public void save() {
        System.out.println("Guice BookDao method: save().");
    }
}

• Service

public interface BookService {

    void save();
}

public class BookServiceImpl implements BookService {

    private final BookDao bookDao;

    @Inject
    public BookServiceImpl(BookDao bookDao) {
        this.bookDao = bookDao;
    }

    @Override
    public void save() {
        System.out.println("Guice BookService method: save().");
        bookDao.save();
    }
}

• Manager

public class BookManager {

    private final BookService bookService;

    @Inject
    public BookManager(BookService bookService) {
        this.bookService = bookService;
    }

    public void test() {
        bookService.save();
    }
}

• Module

public class BookModule extends AbstractModule {

    @Override
    protected void configure() {
        bind(BookDao.class).toInstance(new BookDaoImpl());
        bind(BookService.class).to(BookServiceImpl.class);
    }
}

• 主程序

public class GuiceApp {

    public static void main(String[] args) {
        Guice.createInjector(new BookModule()).getInstance(BookManager.class).test();
    }
}

参考

[1] 慕课网：使用Google Guice实现依赖注入
[2] 代码