给Bean属性注入null值
空字符串值可以使用<value/>元素可用来表示。例如：
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<bean class="ExampleBean"> <property name="email"><value/></property></bean> |
等同于Java代码： exampleBean.setEmail("")。
null值则可以使用<null/>元素可用来表示。例如：
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<bean class="ExampleBean"> <property name="email"><null/></property></bean> |
等同于Java代码：exampleBean.setEmail(null)。
Spring注入bean 为null的相关问题
问题描述
有一个类注入 发现里面的MongoLogInfoDAO始终为null
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@Component("countFunction")public class CountFunction implements AviatorFunction { @Resource(name = "mongoLogInfoDAO") private MongoLogInfoDAO mongoLogInfoDAO; @Override public String getName() { return "count"; } |
原因是竟然是因为使用了 new 方式使用 CountFunction 导致类中的mongoLogInfoDao 无法注入
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AviatorEvaluator.addFunction(new CountFunction()); |
这个是不对的， 为啥？
这个对象是你new出来的 ，不是spring创建的 当然无法DI依赖注入
反之，如果你这个Bean是交易Spring IOC 容器管理的，那也应该报错NoSuchBeanDefinitionException异常
如何处理？
应对这个问题的最好办法是 不要new
还有一种情况spring 注入的时候是null
问题描述
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@Component("functionExecutor")public class FunctionExecutor { protected static final Loggerx LOGGER = Loggerx.getLogger("system"); @Resource(name = "mongoDAO") private MongoDAO mongoDAO; @Resource(name = "prism4001Producer") private SmartMQProducer prism4001Producer; @Resource(name = "whereGreaterThenFunction") private WhereGreaterThenFunction whereGreaterThenFunction; @Resource(name = "countFunction") private CountFunction countFunction; @Resource(name = "devideFunction") private DevideFunction devideFunction; @Resource(name = "selectFunction") private SelectFunction selectFunction; @Resource(name = "whereEqualFunction") private WhereEqualFunction whereEqualFunction; @Resource(name = "timeFunction") private TimeFunction timeFunction; @Resource(name = "whereLessThenFunction") private WhereLessThenFunction whereLessThenFunction; @Resource(name = "whereGreaterThenEqualFunction") private WhereGreaterThenEqualFunction whereGreaterThenEqualFunction; @Resource(name = "whereInFunction") private WhereInFunction whereInFunction; @Resource(name = "greaterThenFunction") private GreaterThenFunction greaterThenFunction; @Resource(name = "regexFunction") private RegexFunction regexFunction; @Resource(name = "maxFunction") private MaxFunction maxFunction; @Resource(name = "minFunction") private MinFunction minFunction; @Resource(name = "equalFunction") private EqualFunction equalFunction; @Resource(name = "lessThenEqualFunction") private LessThenEqualFunction lessThenEqualFunction; @Resource(name = "lessThenFunction") private LessThenFunction lessThenFunction; @Resource(name = "plusFunction") private PlusFunction plusFunction; @Resource(name = "multiFunction") private MultiFunction multiFunction; @Resource(name = "notEqualFunction") private NotEqualFunction notEqualFunction; @Resource(name = "whereNotInFunction") private WhereNotInFunction whereNotInFunction; @Resource(name = "sumFunction") private SumFunction sumFunction; @Resource(name = "minusFunction") private MinusFunction minusFunction; { AviatorEvaluator.addFunction(whereGreaterThenFunction); AviatorEvaluator.addFunction(countFunction); AviatorEvaluator.addFunction(devideFunction); AviatorEvaluator.addFunction(selectFunction); AviatorEvaluator.addFunction(whereEqualFunction); AviatorEvaluator.addFunction(timeFunction); AviatorEvaluator.addFunction(whereLessThenFunction); AviatorEvaluator.addFunction(whereGreaterThenEqualFunction); AviatorEvaluator.addFunction(whereInFunction); AviatorEvaluator.addFunction(greaterThenFunction); AviatorEvaluator.addFunction(regexFunction); AviatorEvaluator.addFunction(maxFunction); AviatorEvaluator.addFunction(minFunction); AviatorEvaluator.addFunction(equalFunction); AviatorEvaluator.addFunction(lessThenEqualFunction); AviatorEvaluator.addFunction(lessThenFunction); AviatorEvaluator.addFunction(plusFunction); AviatorEvaluator.addFunction(multiFunction); AviatorEvaluator.addFunction(notEqualFunction); AviatorEvaluator.addFunction(whereNotInFunction); AviatorEvaluator.addFunction(sumFunction); AviatorEvaluator.addFunction(minusFunction); } |
容器加载这个functionExecutor这个bean的时候，走到静态代码块发现注入的sumFunction ，minusFunction都是null
这个是为什么呢？
spring 执行代码块的时候，其他的bean 还未注入，会导致注入的bean 是null
如何处理？
如果你想 当spring加载 bean 初始化完成之后，自动执行一些初始化方法
使用
@PostConstruct
注解可以实现
以上为个人经验，希望能给大家一个参考，也希望大家多多支持服务器之家。
原文链接：https://blog.csdn.net/xiaojia1100/article/details/51595362
