为什么在不相关的方法上自动布线被忽略 [英] Why Autowired on irrelevant method is ignored
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问题描述
在不相关的方法上使用@Autowired时会发生什么，例如Spring上下文中的@Test:
What happens when you use @Autowired on irrelevant method, as @Test in Spring context:
@Autowired
@Test
public void testDao() {
assert("something", dao.read());
}
似乎什么也没有发生，并且测试成功，在这种情况下是否有办法得到错误/警告?
It seems that nothing happens and Test succeeded, is there a way getting an error/warning in such case?
对于自动连接字段，我得到了预期的异常，例如
For auto wiring a field I'm getting expected exception, e.g.
@Autowired
String nothing;
产生异常:
FAILED CONFIGURATION: @BeforeClass springTestContextPrepareTestInstance
org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'com.package.dao.DAOTest': Unsatisfied dependency expressed through field 'nothing'; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'java.lang.String' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:588)
at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:88)
at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:366)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1264)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.autowireBeanProperties(AbstractAutowireCapableBeanFactory.java:386)
at org.springframework.test.context.support.DependencyInjectionTestExecutionListener.injectDependencies(DependencyInjectionTestExecutionListener.java:118)
at org.springframework.test.context.support.DependencyInjectionTestExecutionListener.prepareTestInstance(DependencyInjectionTestExecutionListener.java:83)
at org.springframework.test.context.TestContextManager.prepareTestInstance(TestContextManager.java:230)
at org.springframework.test.context.testng.AbstractTestNGSpringContextTests.springTestContextPrepareTestInstance(AbstractTestNGSpringContextTests.java:149)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.testng.internal.MethodInvocationHelper.invokeMethod(MethodInvocationHelper.java:124)
at org.testng.internal.MethodInvocationHelper.invokeMethodConsideringTimeout(MethodInvocationHelper.java:59)
at org.testng.internal.Invoker.invokeConfigurationMethod(Invoker.java:455)
at org.testng.internal.Invoker.invokeConfigurations(Invoker.java:222)
at org.testng.internal.Invoker.invokeConfigurations(Invoker.java:142)
at org.testng.internal.TestMethodWorker.invokeBeforeClassMethods(TestMethodWorker.java:168)
at org.testng.internal.TestMethodWorker.run(TestMethodWorker.java:105)
at org.testng.TestRunner.privateRun(TestRunner.java:648)
at org.testng.TestRunner.run(TestRunner.java:505)
at org.testng.SuiteRunner.runTest(SuiteRunner.java:455)
at org.testng.SuiteRunner.runSequentially(SuiteRunner.java:450)
at org.testng.SuiteRunner.privateRun(SuiteRunner.java:415)
at org.testng.SuiteRunner.run(SuiteRunner.java:364)
at org.testng.SuiteRunnerWorker.runSuite(SuiteRunnerWorker.java:52)
at org.testng.SuiteRunnerWorker.run(SuiteRunnerWorker.java:84)
at org.testng.TestNG.runSuitesSequentially(TestNG.java:1208)
at org.testng.TestNG.runSuitesLocally(TestNG.java:1137)
at org.testng.TestNG.runSuites(TestNG.java:1049)
at org.testng.TestNG.run(TestNG.java:1017)
at org.testng.remote.AbstractRemoteTestNG.run(AbstractRemoteTestNG.java:114)
at org.testng.remote.RemoteTestNG.initAndRun(RemoteTestNG.java:251)
at org.testng.remote.RemoteTestNG.main(RemoteTestNG.java:77)
Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'java.lang.String' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
at org.springframework.beans.factory.support.DefaultListableBeanFactory.raiseNoMatchingBeanFound(DefaultListableBeanFactory.java:1493)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1104)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1066)
at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:585)
... 34 more
将@Autowired添加到任何方法(不仅用于测试)时，也会被忽略:
It's ignored also when adding @Autowired to any method (not only test):
@Autowired
private void doNothing() {
}
推荐答案
@Autowired的目的是注入要从中注入代码的依赖项.
Spring支持三种类型，
The purpose of @Autowired is to inject the dependency that is going to be used by the code you are injecting from .
There are three types that Spring supports,
- 设置方法注入
- 构造函数注入
- 现场或财产注入
构造函数和方法都必须有一个参数，因为Spring会注入所用参数的类型，否则Spring会混淆注入的内容而只是忽略.在字段注入中，它将注入字段的类型.
Both the constructor and method must have a parameter because Spring will inject the type of the parameter used, Otherwise Spring will be confused what to inject and simply ignores. In the field injection, it will inject the type of the field.
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