实例化bean时Spring抛出NoClassDefFoundError

Question

I have a spring bean.

@Component
public class Omg {

    public void omg() throws IOException {
        HttpServletRequest request = null;
        InputStream is = request.getInputStream();
        is.read();
    }

}

I am not using it in a servlet container. This is just for the sake of example.

ApplicationContext context = new ClassPathXmlApplicationContext("spring.xml");

This line throws exception java.lang.NoClassDefFoundError: javax/servlet/ServletInputStream. Servlet api is not in classpath in runtime. Okay, I understand that NoClassDefFoundError should be thrown when omg method runs. The question is: why is it thrown when spring tries to instantiate the bean and why ServletInputStream rather than HttpServlerRequest ?

Exception in thread "main" java.lang.NoClassDefFoundError: javax/servlet/ServletInputStream
    at java.lang.Class.getDeclaredConstructors0(Native Method)
    at java.lang.Class.privateGetDeclaredConstructors(Class.java:2532)
    at java.lang.Class.getDeclaredConstructors(Class.java:1901)
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.determineCandidateConstructors(AutowiredAnnotationBeanPostProcessor.java:234)

UPDATE: However this works fine

public class A {}

public class B {

    public void method() {
        A a = new A();
    } 

}

public class C {

    public static void main(String[] args) {
        B b = new B();
    }

}

compile all three classes. remove A.class. run main method of C class. It works fine.

Answer 1

public class NoClassDefFoundError extends LinkageError

Thrown if the Java Virtual Machine or a ClassLoader instance tries to load in the definition of a class (as part of a normal method call or as part of creating a new instance using the new expression ) and no definition of the class could be found.

public class A {}

public class B {
  public void m(A a) {
  }

  public static void main(String[] args) {
     B b = new B();
  }
}

javac A.java // OK

javac B.java // OK

// remove A.class

java B

Exception in thread "main" java.lang.NoClassDefFoundError: A
        at java.lang.Class.getDeclaredMethods0(Native Method)
        at java.lang.Class.privateGetDeclaredMethods(Unknown Source)
        at java.lang.Class.getMethod0(Unknown Source)
        at java.lang.Class.getMethod(Unknown Source)