Spring 框架（四）（Spring依賴注入 一）

依賴注入

當編寫一個複雜 的java應用程序時，應用程序類應該儘可能獨立於其他類來增加這些類重用的可能性。依賴注入可以理解爲有助於將各種類並在一起，同時保持各種類的獨立。

如：private Dog  dog；//將其他類作爲本類的屬性

public class Demo{
    private Dog dog;
      
    public Demo(Dog dog){  //構造函數注入
       this.dog=dog;
    }
    
    public void setDog(Dog dog){   //setter注入
        this.dog=dog;
    }
}

 

依賴注入有兩種

序號	依賴注入類型 & 描述
1	Constructor-based dependency injection 當容器調用帶有多個參數的構造函數類時，實現基於構造函數的 DI，每個代表在其他類中的一個依賴關係。
2	Setter-based dependency injection 基於 setter 方法的 DI 是通過在調用無參數的構造函數或無參數的靜態工廠方法實例化 bean 之後容器調用 beans 的 setter 方法來實現的。

 

 

Spring基於構造函數的依賴注入

package dc.com;

public class Cat {
    private Dog dog;

    public Cat(Dog dog){
        System.out.println("this is CatClass....");
        this.dog=dog;
    }
    public void CatMe(){
        dog.Dogme();
    }
}

package dc.com;

public class Dog {
    public Dog(){
        System.out.println("this is DogClass.....");
    }

    public void Dogme(){
        System.out.println("this is Dogme......");
    }
}

 

package dc.com;

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

public class MainApp {
    public static void main(String[] args) {
        ApplicationContext applicationContext=new ClassPathXmlApplicationContext("beans.xml");
        Cat cat= (Cat) applicationContext.getBean("cat");
        cat.CatMe();

    }
}

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:p="http://www.springframework.org/schema/p"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans-3.2.xsd">
    <!-- 由 Spring容器創建該類的實例對象 -->
    <bean id="cat" class="dc.com.Cat" >
        <constructor-arg ref="dog"></constructor-arg>
    </bean>
    <bean id="dog" class="dc.com.Dog"/>
</beans>

 

Spring基於setter方法的依賴注入

package com.tutorialspoint;
public class TextEditor {
   private SpellChecker spellChecker;
   // a setter method to inject the dependency.
   public void setSpellChecker(SpellChecker spellChecker) {
      System.out.println("Inside setSpellChecker." );
      this.spellChecker = spellChecker;
   }
   // a getter method to return spellChecker
   public SpellChecker getSpellChecker() {
      return spellChecker;
   }
   public void spellCheck() {
      spellChecker.checkSpelling();
   }
}

package com.tutorialspoint;
public class SpellChecker {
   public SpellChecker(){
      System.out.println("Inside SpellChecker constructor." );
   }
   public void checkSpelling() {
      System.out.println("Inside checkSpelling." );
   }  
}

 

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("Beans.xml");
      TextEditor te = (TextEditor) context.getBean("textEditor");
      te.spellCheck();
   }
}

<?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">
      <property name="spellChecker" ref="spellChecker"/>
   </bean>

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

</beans>

可以使用 p-namespace方式

<?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"
    p:spouse-ref="spellchecker">
      
   </bean>

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

</beans>