Spring Dependency Injection 简明教程
Spring DI - Constructor-Based
当容器使用一系列参数调用类构造函数,每个参数表示对其他类的依赖关系时,就完成了基于构造函数的 DI。
Constructor-Based DI is accomplished when the container invokes a class constructor with a number of arguments, each representing a dependency on the other class.
Example
以下示例展示了一个类 TextEditor,它只能通过构造函数注入进行依赖注入。
The following example shows a class TextEditor that can only be dependency-injected with constructor 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 −
-
TextEditor.java − A class containing a SpellChecker as dependency.
-
SpellChecker.java − A dependency class.
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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;
public TextEditor(SpellChecker spellChecker) {
System.out.println("Inside TextEditor constructor." );
this.spellChecker = spellChecker;
}
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
package com.tutorialspoint;
public class SpellChecker {
public SpellChecker(){
System.out.println("Inside SpellChecker constructor." );
}
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();
}
}
以下是 applicationcontext.xml 配置文件,它包含基于构造函数的注入配置 −
Following is the configuration file applicationcontext.xml which has configuration for the constructor-based injection −
<?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">
<constructor-arg ref = "spellChecker"/>
</bean>
<!-- Definition for spellChecker bean -->
<bean id = "spellChecker" class = "com.tutorialspoint.SpellChecker"></bean>
</beans>
Output
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 constructor.
Inside TextEditor constructor.
Inside checkSpelling.