public class StudentA { 
 
  private StudentB studentB ; 
 
  public void setStudentB(StudentB studentB) { 
    this.studentB = studentB; 
  } 
 
  public StudentA() { 
  } 
   
  public StudentA(StudentB studentB) { 
    this.studentB = studentB; 
  } 
}

public class StudentB { 
 
  private StudentC studentC ; 
 
  public void setStudentC(StudentC studentC) { 
    this.studentC = studentC; 
  } 
   
  public StudentB() { 
  } 
 
  public StudentB(StudentC studentC) { 
    this.studentC = studentC; 
  } 
}

public class StudentC { 
 
  private StudentA studentA ; 
 
  public void setStudentA(StudentA studentA) { 
    this.studentA = studentA; 
  } 
 
  public StudentC() { 
  } 
  
  public StudentC(StudentA studentA) { 
    this.studentA = studentA; 
  } 
}

<bean id="a" class="com.zfx.student.StudentA"> 
  <constructor-arg index="0" ref="b"></constructor-arg> 
</bean> 
<bean id="b" class="com.zfx.student.StudentB"> 
  <constructor-arg index="0" ref="c"></constructor-arg> 
</bean> 
<bean id="c" class="com.zfx.student.StudentC"> 
  <constructor-arg index="0" ref="a"></constructor-arg> 
</bean>

public class Test { 
   public static void main(String[] args) { 
     ApplicationContext context = new ClassPathXmlApplicationContext("com/zfx/student/applicationContext.xml"); 
     //System.out.println(context.getBean("a", StudentA.class)); 
   } 
 }

<!--scope="singleton"(默認(rèn)就是單例方式) --> 
<bean id="a" class="com.zfx.student.StudentA" scope="singleton"> 
  <property name="studentB" ref="b"></property> 
</bean> 
<bean id="b" class="com.zfx.student.StudentB" scope="singleton"> 
  <property name="studentC" ref="c"></property> 
</bean> 
<bean id="c" class="com.zfx.student.StudentC" scope="singleton"> 
  <property name="studentA" ref="a"></property> 
</bean>

 public class Test { 
   public static void main(String[] args) { 
     ApplicationContext context = new ClassPathXmlApplicationContext("com/zfx/student/applicationContext.xml"); 
     System.out.println(context.getBean("a", StudentA.class)); 
   } 
 } 

/** Cache of singleton objects: bean name --> bean instance（緩存單例實(shí)例化對象的Map集合） */ 
  private final Map<String, Object> singletonObjects = new ConcurrentHashMap<String, Object>(64); 
   
  /** Cache of singleton factories: bean name --> ObjectFactory（單例的工廠Bean緩存集合） */ 
  private final Map<String, ObjectFactory> singletonFactories = new HashMap<String, ObjectFactory>(16); 
   
  /** Cache of early singleton objects: bean name --> bean instance（早期的單身對象緩存集合） */ 
  private final Map<String, Object> earlySingletonObjects = new HashMap<String, Object>(16); 
   
  /** Set of registered singletons, containing the bean names in registration order（單例的實(shí)例化對象名稱集合） */ 
  private final Set<String> registeredSingletons = new LinkedHashSet<String>(64); 
  /** 
   * 添加單例實(shí)例 
   * 解決循環(huán)引用的問題 
   * Add the given singleton factory for building the specified singleton 
   * if necessary. 
   * <p>To be called for eager registration of singletons, e.g. to be able to 
   * resolve circular references. 
   * @param beanName the name of the bean 
   * @param singletonFactory the factory for the singleton object 
   */ 
  protected void addSingletonFactory(String beanName, ObjectFactory singletonFactory) { 
    Assert.notNull(singletonFactory, "Singleton factory must not be null"); 
    synchronized (this.singletonObjects) { 
      if (!this.singletonObjects.containsKey(beanName)) { 
        this.singletonFactories.put(beanName, singletonFactory); 
        this.earlySingletonObjects.remove(beanName); 
        this.registeredSingletons.add(beanName); 
      } 
    } 
  }

<bean id="a" class="com.zfx.student.StudentA" <span style="color:#FF0000;">scope="prototype"</span>> 
    <property name="studentB" ref="b"></property> 
  </bean> 
  <bean id="b" class="com.zfx.student.StudentB" <span style="color:#FF0000;">scope="prototype"</span>> 
    <property name="studentC" ref="c"></property> 
  </bean> 
  <bean id="c" class="com.zfx.student.StudentC" <span style="color:#FF0000;">scope="prototype"</span>> 
    <property name="studentA" ref="a"></property> 
  </bean>

public class Test { 
  public static void main(String[] args) { 
    ApplicationContext context = new ClassPathXmlApplicationContext("com/zfx/student/applicationContext.xml"); 
    <strong>//此時(shí)必須要獲取Spring管理的實(shí)例，因?yàn)楝F(xiàn)在scope="prototype" 只有請求獲取的時(shí)候才會實(shí)例化對象</strong> 
    System.out.println(context.getBean("a", StudentA.class)); 
  } 
}