java - Spring 3 @Autowired 注解问题

Question

我一直在查看一些有关 Spring 框架入门的教程，并遇到了 this one .完成之后，我遇到了以下错误。 (我已经更新为使用 spring 框架的版本 3，但我仍然遇到相同的错误。

简而言之，我在调用 AutoWired 类的方法时遇到 NullPointerException。

我的类(class)是 SayHello:

public class SayHello {

private String name;

public void setName(String name) {
    this.name = name;
}

public String getName() {
    return name;
}

public void greet() {
    System.out.println("Hello " + getName());
}

}

然后我在/src/test/resources/applicationContext.xml 中设置以下内容。

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:context="http://www.springframework.org/schema/context"
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="hello" class="package.SayHello">
    <property name="name" value="John Smith" />
  </bean

最后我有了 AppTest 类，我在其中尝试自动连接 SayHello 对象进行测试。

public class AppTest {

@Autowired
private SayHello hello;

@Test
public void testApp()
{
    hello.greet();
    Assert.assertTrue( true );
}
}

当我尝试运行 AppTest 时出现以下错误:

java.lang.NullPointerException
at package.AppTest.testApp(AppTest.java:19)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:601)
at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:47)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:44)
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:271)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:70)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:50)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:238)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:63)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:236)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:53)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:229)
at org.junit.runners.ParentRunner.run(ParentRunner.java:309)
at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50)
at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)

我已经查看了关于 stackoverflow 的各种文章和问题，但在尝试了一些但一无所获之后，我想我应该创建一个新帖子。

干杯。

如果有帮助，这是我正在使用的依赖项(Spring v3.2.1):

<dependencies>

<!-- JUnit -->
<dependency>
    <groupId>junit</groupId>
    <artifactId>junit</artifactId>
    <version>4.11</version>
    <scope>test</scope>
</dependency>


<!-- Spring -->
<dependency>
  <groupId>org.springframework</groupId>
  <artifactId>spring-beans</artifactId>
  <version>${org.springframework.version}</version>
</dependency>

<dependency>
  <groupId>org.springframework</groupId>
  <artifactId>spring-core</artifactId>
  <version>${org.springframework.version}</version>
</dependency>

<dependency>
  <groupId>org.springframework</groupId>
  <artifactId>spring-webmvc</artifactId>
  <version>${org.springframework.version}</version>
</dependency>

<dependency>
  <groupId>org.springframework</groupId>
  <artifactId>spring-context-support</artifactId>
  <version>${org.springframework.version}</version>
</dependency>

<dependency>
  <groupId>org.springframework</groupId>
  <artifactId>spring-aop</artifactId>
  <version>${org.springframework.version}</version>
</dependency>

<dependency>
  <groupId>org.springframework</groupId>
  <artifactId>spring-jms</artifactId>
  <version>${org.springframework.version}</version>
</dependency>

<dependency>
  <groupId>org.springframework</groupId>
  <artifactId>spring-context</artifactId>
  <version>${org.springframework.version}</version>
</dependency>

更新

我还尝试在主应用程序中使用@Autowired 注释，如下所示。并且仍然得到 NullPointerException 错误。

public class App 
{   
    @Autowired
    private static SayHello hello;

    public static void main( String[] args )
    {
       hello.greet();
    }
}

Answer 1

您需要在 AppTest 上添加一些注释:

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(locations = "classpath:/applicationContext.xml")

这些注解是在spring-test中定义的，所以也加上这个依赖:

<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-test</artifactId>
    <version>${org.springframework.version}</version>
    <scope>test</scope>
</dependency>