Spring Dependency Injection 简明教程

Spring DI - Static Factory

Spring 提供了一个使用 factory-method 属性注入相关依赖项的选项。

Spring provides an option to inject dependency using factory-method attribute.

Example

以下示例展示了 TextEditor 类，它只能使用纯基于 setter 的注入进行依赖项注入。

The following example shows a class TextEditor that can only be dependency-injected using pure setter-based injection.

让我们更新在 Spring DI - Create Project 章节中创建的项目。我们将添加以下文件 −

Let’s update the project created in Spring DI - Create Project chapter. We’re adding following files −

  1. TextEditor.java − A class containing a SpellChecker as dependency.

  2. SpellChecker.java − A dependency class.

  3. MainApp.java − Main application to run and test.

以下为 TextEditor.java 文件的内容 −

Here is the content of TextEditor.java file −

package com.tutorialspoint;

public class TextEditor {
   private SpellChecker spellChecker;
   private String name;

   public void setSpellChecker( SpellChecker spellChecker ){
      this.spellChecker = spellChecker;
   }
   public SpellChecker getSpellChecker() {
      return spellChecker;
   }
   public void setName(String name) {
      this.name = name;
   }
   public String getName() {
      return name;
   }
   public void spellCheck() {
      spellChecker.checkSpelling();
   }
}

以下是另一个依赖类文件 SpellChecker.java 的内容 −

Following is the content of another dependent class file SpellChecker.java −

这个类构造函数是私有的。所以无法用 new 运算符直接用其他对象创建其对象。它有一个静态工厂方法来获取一个实例。

This class constructor is private. So its object can not be created directly using new operator by other object. It has a static factory method to get an instance.

package com.tutorialspoint;

public class SpellChecker {
   private SpellChecker(){
      System.out.println("Inside SpellChecker constructor." );
   }
   public static SpellChecker getInstance() {
      System.out.println("Inside SpellChecker getInstance." );
      return new SpellChecker();
   }
   public void checkSpelling(){
      System.out.println("Inside checkSpelling." );
   }
}

以下是 MainApp.java 文件的内容−

Following is the content of the MainApp.java file −

package com.tutorialspoint;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class MainApp {
   public static void main(String[] args) {
      ApplicationContext context = new ClassPathXmlApplicationContext("applicationcontext.xml");
      TextEditor te = (TextEditor) context.getBean("textEditor");
      te.spellCheck();
   }
}

下面是配置了自动装配的配置 applicationcontext.xml −

Following is the configuration file applicationcontext.xml which has configuration for autowiring byName −

<?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-3.0.xsd">

   <!-- Definition for textEditor bean -->
   <bean id = "textEditor" class = "com.tutorialspoint.TextEditor" autowire = "byName">
      <property name = "name" value = "Generic Text Editor" />
   </bean>

   <!-- Definition for spellChecker bean -->
   <bean id = "spellChecker" class = "com.tutorialspoint.SpellChecker" factory-method="getInstance"></bean>
</beans>

完成源文件和 Bean 配置文件创建后，我们运行该应用程序。如果您的应用程序一切正常，它将打印以下消息−

Once you are done creating the source and bean configuration files, let us run the application. If everything is fine with your application, it will print the following message −

Inside SpellChecker getInstance.
Inside SpellChecker constructor.
Inside checkSpelling.