Spring@required&@强制注释

Question

package com.practice.spring;

import org.springframework.beans.factory.annotation.Required;

import com.apress.springrecipes.sequence.Mandatory;

public class BeanClass {

    private int count;
    private String prefix;

    public BeanClass() {
        System.out.println("Default Constructor");
    }

    public BeanClass(int count, String prefix) {
        this.count = count;
        this.prefix = prefix;
        System.out.println(prefix+count);
    }

    @Required
    public void setCount(int count) {
        this.count = count;
    }

    @Mandatory
    public void setPrefix(String prefix) {
        this.prefix = prefix;
    }

    @Override
    public String toString() {
        return prefix+count;
    }

}

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:context="http://www.springframework.org/schema/context"
       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.xsd
            http://www.springframework.org/schema/context
            http://www.springframework.org/schema/context/spring-context.xsd">

    <context:annotation-config />

    <bean id="beanClass1"
          class="com.practice.spring.BeanClass">
        <property name="count" value="1" />
        <property name="prefix" value="Bean" />
    </bean>
    <bean id="beanClass2"
          class="com.practice.spring.BeanClass">
        <constructor-arg value="2" />
        <constructor-arg value="Bean" />
    </bean>
    <bean id="beanClass3"
          class="com.practice.spring.BeanClass">
        <constructor-arg>
            <value>3</value>
        </constructor-arg>
        <constructor-arg>
            <value>Bean</value>
        </constructor-arg>
    </bean>
</beans>

ApplicationContext context = new ClassPathXmlApplicationContext("beans.xml");

问题：

count属性是必需的&前缀是必需的。如果您看到beanClass2，我将通过构造函数设置属性，在beanClass3中也是如此

但是当我执行代码时，它抛出异常。让我困惑的重要事情是：

2014年12月9日8:47:33 PM org.springframework.beans.factory.support.defaultsingletonbeanregistry destroySingletons信息：在org.springframework.beans.factory.support.defaultListablebeanFactory@4aed64:定义beans[org.springframework.beans.factory.defaultListablebeanFactory@4aed64:defining Anclass3]；线程“main”org.springframework.beans.factory.BeanCreationException中的工厂层次结构异常根目录：创建类路径资源[beans.xml]中定义的名为“BeanClass2”的bean时出错：bean初始化失败；嵌套异常是org.springframework.beans.factory.beanInitializationException：在org.springframework.beans.factory.support.abstractauTawaitaPableBeanFactory.docreateBean（abstractauTauTowireCapableBeanFactory.java:527)在org.springframework.beans.factory.support.abstractauTauTowireCapableBeanFactory.createBean（tory.java:291)在org.springframework.beans.factory.support.defaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)在org.springframework.beans.factory.support.abstractBeanFactory.dogetbean(abstractBeanFactory.java:288)在factory.java:563)位于org.springframework.context.support.AbstractApplicationContext.FinishBeanFactoryInitialization（AbstractApplicationContext.java:872)在org.springframework.context.support.AbstractApplicationContext.Refresh（AbstractApplicationContext.java:423)在org.springframework.context.support.ClasspathXMLApplicationContext.(classpathXMLApplicationContext.(139)在AninitializationException：在org.springframework.beans.factory.annotation.RequiredanNotationBeanPostProcessor.PostProcessPropertyValues（RequiredanNotationBeanPostProcessor.java:149)在org.springframework.beans.factory.support.abstractaUtaItaPableBeanFactory.populateBean（AbstractaUtaIreCableBeanFactory.java:1064)在oCreateBean(AbstractaUtowireCapableBeanFactory.java:517)...11多

Answer 1

@Required意味着您正在使用setter注入，而不是构造函数注入。它们被设计成两个选项--而不是同时做两个选项。

请注意Spring的博客-

@Required允许您指示Spring为您检查所需的依赖项。如果您不适合使用构造函数注入，或者出于其他原因，您更喜欢setter注入，@Required是应该做的。

@Required将一个方法（通常是JavaBean setter方法）标记为“Required”：也就是说，必须将setter方法配置为使用值注入依赖项。

需求表示法

因此，您将其标记为必须注入依赖项-而不是注入构造函数。