创建spring boot ConfigurationProperties Map<String, Object>时的空指针

Question

创建 Spring Boot ConfigurationProperties Map 时出现空指针异常。属性类是

@Component
@ConfigurationProperties(prefix = "thing")
public class ThingProperties {

 private Map<String, ThingLayout> layouts;

 public Map<String, ThingLayout> getLayouts() {
     return layouts == null ? new HashMap<>() : layouts;
 }

 public void setLayouts(final Map<String, ThingLayout> layouts) {
     this.layouts = new HashMap(layouts);
 }
}

ThingLayout 是一个简单的 pojo，具有属性文件指定的正确属性：

things.layouts:
 3042:
  itemPageIndex: 1
  itemX: 1960
  itemY: 890
  itemWidth: 400
  itemHeight: 70
  itemPattern: dd MMMM yyyy
 2151:
  itemPageIndex: 0
  itemX: 2000
  itemY: 796
  itemWidth: 500
  itemHeight: 70
  itemPattern: dd/MM/yyyy

目的是绑定属性，我将能够做类似的事情

thingProperties.getLayouts().get(3042).getItemX();

我得到的例外是

Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'thingProperties': Could not bind properties to ThingProperties (prefix=things, ignoreInvalidFields=false, ignoreUnknownFields=true, ignoreNestedProperties=false); nested exception is java.lang.IllegalArgumentException: Target object must not be null
at org.springframework.boot.context.properties.ConfigurationPropertiesBindingPostProcessor.postProcessBeforeInitialization(ConfigurationPropertiesBindingPostProcessor.java:339) ~[spring-boot-1.3.2.RELEASE.jar:1.3.2.RELEASE]
at org.springframework.boot.context.properties.ConfigurationPropertiesBindingPostProcessor.postProcessBeforeInitialization(ConfigurationPropertiesBindingPostProcessor.java:289) ~[spring-boot-1.3.2.RELEASE.jar:1.3.2.RELEASE]
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyBeanPostProcessorsBeforeInitialization(AbstractAutowireCapableBeanFactory.java:408) ~[spring-beans-4.2.4.RELEASE.jar:4.2.4.RELEASE]
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1570) ~[spring-beans-4.2.4.RELEASE.jar:4.2.4.RELEASE]
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:545) ~[spring-beans-4.2.4.RELEASE.jar:4.2.4.RELEASE]
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:482) ~[spring-beans-4.2.4.RELEASE.jar:4.2.4.RELEASE]
at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:306) ~[spring-beans-4.2.4.RELEASE.jar:4.2.4.RELEASE]
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230) ~[spring-beans-4.2.4.RELEASE.jar:4.2.4.RELEASE]
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:302) ~[spring-beans-4.2.4.RELEASE.jar:4.2.4.RELEASE]
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:197) ~[spring-beans-4.2.4.RELEASE.jar:4.2.4.RELEASE]
at org.springframework.beans.factory.support.DefaultListableBeanFactory.findAutowireCandidates(DefaultListableBeanFactory.java:1192) ~[spring-beans-4.2.4.RELEASE.jar:4.2.4.RELEASE]
at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1116) ~[spring-beans-4.2.4.RELEASE.jar:4.2.4.RELEASE]
at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1014) ~[spring-beans-4.2.4.RELEASE.jar:4.2.4.RELEASE]
at org.springframework.beans.factory.support.ConstructorResolver.resolveAutowiredArgument(ConstructorResolver.java:813) ~[spring-beans-4.2.4.RELEASE.jar:4.2.4.RELEASE]
at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:741) ~[spring-beans-4.2.4.RELEASE.jar:4.2.4.RELEASE]
... 47 common frames omitted
Caused by: java.lang.IllegalArgumentException: Target object must not be null
at org.springframework.util.Assert.notNull(Assert.java:115) ~[spring-core-4.2.4.RELEASE.jar:4.2.4.RELEASE]
at org.springframework.beans.AbstractNestablePropertyAccessor.setWrappedInstance(AbstractNestablePropertyAccessor.java:205) ~[spring-beans-4.2.4.RELEASE.jar:4.2.4.RELEASE]
at org.springframework.beans.BeanWrapperImpl.setWrappedInstance(BeanWrapperImpl.java:138) ~[spring-beans-4.2.4.RELEASE.jar:4.2.4.RELEASE]
at org.springframework.beans.AbstractNestablePropertyAccessor.<init>(AbstractNestablePropertyAccessor.java:165) ~[spring-beans-4.2.4.RELEASE.jar:4.2.4.RELEASE]
at org.springframework.beans.BeanWrapperImpl.<init>(BeanWrapperImpl.java:131) ~[spring-beans-4.2.4.RELEASE.jar:4.2.4.RELEASE]
at org.springframework.beans.BeanWrapperImpl.newNestedPropertyAccessor(BeanWrapperImpl.java:223) ~[spring-beans-4.2.4.RELEASE.jar:4.2.4.RELEASE]
at org.springframework.beans.BeanWrapperImpl.newNestedPropertyAccessor(BeanWrapperImpl.java:63) ~[spring-beans-4.2.4.RELEASE.jar:4.2.4.RELEASE]
at org.springframework.beans.AbstractNestablePropertyAccessor.getNestedPropertyAccessor(AbstractNestablePropertyAccessor.java:853) ~[spring-beans-4.2.4.RELEASE.jar:4.2.4.RELEASE]
at org.springframework.beans.AbstractNestablePropertyAccessor.getPropertyAccessorForPropertyPath(AbstractNestablePropertyAccessor.java:813) ~[spring-beans-4.2.4.RELEASE.jar:4.2.4.RELEASE]
at org.springframework.beans.AbstractNestablePropertyAccessor.getPropertyHandler(AbstractNestablePropertyAccessor.java:724) ~[spring-beans-4.2.4.RELEASE.jar:4.2.4.RELEASE]
at org.springframework.beans.AbstractNestablePropertyAccessor.getPropertyType(AbstractNestablePropertyAccessor.java:485) ~[spring-beans-4.2.4.RELEASE.jar:4.2.4.RELEASE]
at org.springframework.boot.bind.RelaxedDataBinder.resolvePropertyName(RelaxedDataBinder.java:421) ~[spring-boot-1.3.2.RELEASE.jar:1.3.2.RELEASE]
at org.springframework.boot.bind.RelaxedDataBinder.getActualPropertyName(RelaxedDataBinder.java:385) ~[spring-boot-1.3.2.RELEASE.jar:1.3.2.RELEASE]
at org.springframework.boot.bind.RelaxedDataBinder.initializePath(RelaxedDataBinder.java:273) ~[spring-boot-1.3.2.RELEASE.jar:1.3.2.RELEASE]
at org.springframework.boot.bind.RelaxedDataBinder.initializePath(RelaxedDataBinder.java:308) ~[spring-boot-1.3.2.RELEASE.jar:1.3.2.RELEASE]
at org.springframework.boot.bind.RelaxedDataBinder.initializePath(RelaxedDataBinder.java:308) ~[spring-boot-1.3.2.RELEASE.jar:1.3.2.RELEASE]
at org.springframework.boot.bind.RelaxedDataBinder.normalizePath(RelaxedDataBinder.java:259) ~[spring-boot-1.3.2.RELEASE.jar:1.3.2.RELEASE]
at org.springframework.boot.bind.RelaxedDataBinder.modifyProperty(RelaxedDataBinder.java:240) ~[spring-boot-1.3.2.RELEASE.jar:1.3.2.RELEASE]
at org.springframework.boot.bind.RelaxedDataBinder.modifyProperties(RelaxedDataBinder.java:155) ~[spring-boot-1.3.2.RELEASE.jar:1.3.2.RELEASE]
at org.springframework.boot.bind.RelaxedDataBinder.doBind(RelaxedDataBinder.java:128) ~[spring-boot-1.3.2.RELEASE.jar:1.3.2.RELEASE]
at org.springframework.validation.DataBinder.bind(DataBinder.java:715) ~[spring-context-4.2.4.RELEASE.jar:4.2.4.RELEASE]
at org.springframework.boot.bind.PropertiesConfigurationFactory.doBindPropertiesToTarget(PropertiesConfigurationFactory.java:269) ~[spring-boot-1.3.2.RELEASE.jar:1.3.2.RELEASE]
at org.springframework.boot.bind.PropertiesConfigurationFactory.bindPropertiesToTarget(PropertiesConfigurationFactory.java:241) ~[spring-boot-1.3.2.RELEASE.jar:1.3.2.RELEASE]
at org.springframework.boot.context.properties.ConfigurationPropertiesBindingPostProcessor.postProcessBeforeInitialization(ConfigurationPropertiesBindingPostProcessor.java:334) ~[spring-boot-1.3.2.RELEASE.jar:1.3.2.RELEASE]
... 61 common frames omitted

Answer 1

经过大量调试，最终解决方案非常简单。如果我将我的属性类更改为以下内容。

@Component
@ConfigurationProperties(prefix = "thing")
public class ThingProperties {

 private Map<String, ThingLayout> layouts = new HashMap<>();

 public Map<String, ThingLayout> getLayouts() {
     return layouts;
 }

 public void setLayouts(final Map<String, ThingLayout> layouts) {
     this.layouts = new HashMap(layouts);
 }
}

请注意，我现在在 getter 之外初始化布局对象。

Spring 试图为每个映射键创建一个默认值

org.springframework.beans.AbstractNestablePropertyAccessor#setDefaultValue(org.springframework.beans.AbstractNestablePropertyAccessor.PropertyTokenHolder)

默认值创建工作正常，但该值未在地图中正确设置

org.springframework.beans.AbstractNestablePropertyAccessor#setPropertyValue(org.springframework.beans.AbstractNestablePropertyAccessor.PropertyTokenHolder, org.springframework.beans.PropertyValue)