Spring 3 @Autowired注释问题

Question

I've been taking a look at some tutorials for getting started with the Spring Framework and came across this one . After following it through, I ran into the errors below. (I have since updated to use version 3 of the spring framework and I am still getting the same errors.

In short, I am getting a NullPointerException where I call a method on an AutoWired class.

My Class is 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());
}

}

I then set the following in /src/test/resources/applicationContext.xml.

<?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

And finally I have the AppTest class where I try to AutoWire a SayHello object to test.

public class AppTest {

@Autowired
private SayHello hello;

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

When I try to run AppTest I get the following error:

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)

I've had a look at various articles and questions on stackoverflow but after trying a few and not getting anywhere, thought I'd create a new post.

Cheers.

If it helps, heres the dependencies that I'm using (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>

Update

I've also tried using the @Autowired annotation in the main application as follows. And still get a NullPointerException error.

public class App 
{   
    @Autowired
    private static SayHello hello;

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

Answer 1

You will need some annotations on AppTest :

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

These annotations are defined in spring-test, so add this dependency as well:

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

Answer 2

The @Autowired annotation will only work, if AppTest itself is managed by Spring. It looks like you are testing your setup in a simple unit test. This won't work. If you want autowiring in JUnit tests, you will have to look at the Testing support of Spring. But that's a completely different topic.

Answer 3

In the tutorial you have linked this code instantiates the bean:

BeanFactory factory = new XmlBeanFactory(
   new ClassPathResource("application-context.xml"));

SayHello hello = (SayHello) factory.getBean("hello");

Your SayHello bean is null.