Spring DI依赖注入

依赖注入

代码实例

public class User {
    private String name;
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
}

Beans.xml

<bean id="user" class="com.bean.User">
    <property name="name">
        <value>yudesong</value>
    </property>
</bean>
<bean id="user" class="com.bean.User">
    <constructor-arg value="name" index="0">
    </constructor-arg>  
</bean>

注入内部 Beans

TextEditor.java

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();
   }
}

SpellChecker.java

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

Beans.xml

<bean id="textEditor" class="com.tutorialspoint.TextEditor">
    <property name="spellChecker">
        <bean id="spellChecker" class="com.tutorialspoint.SpellChecker"/>
    </property>
</bean>

注入集合

Spring 提供了四种类型的集合的配置元素

List addressList;
Set  addressSet;
Map  addressMap;
Properties addressProp;
<!-- Definition for javaCollection -->
<bean id="javaCollection" class="com.tutorialspoint.JavaCollection">
    <!-- results in a setAddressList(java.util.List) call -->
      <property name="addressList">
         <list>
            <value>INDIA</value>
            <value>Pakistan</value>
            <value>USA</value>
            <value>USA</value>
         </list>
      </property>
      <!-- results in a setAddressSet(java.util.Set) call -->
      <property name="addressSet">
         <set>
            <value>INDIA</value>
            <value>Pakistan</value>
            <value>USA</value>
            <value>USA</value>
        </set>
      </property>
      <!-- results in a setAddressMap(java.util.Map) call -->
      <property name="addressMap">
         <map>
            <entry key="1" value="INDIA"/>
            <entry key="2" value="Pakistan"/>
            <entry key="3" value="USA"/>
            <entry key="4" value="USA"/>
         </map>
      </property>
      <!-- results in a setAddressProp(java.util.Properties) call -->
      <property name="addressProp">
         <props>
            <prop key="one">INDIA</prop>
            <prop key="two">Pakistan</prop>
            <prop key="three">USA</prop>
            <prop key="four">USA</prop>
         </props>
</property>
//处理NULL
<bean id="..." class="exampleBean">
   <property name="email"><null/></property>
</bean>
//处理空字符串
<bean id="..." class="exampleBean">
   <property name="email" value=""/>
</bean>