Spring autowire stops working for classes on the Tomcat classpath

问题

Inside my library FooLibrary.jar Spring instantiates class com.example.FooImpl which has a property bars. I have lots of Bar instances also instantiated by Spring. A set of bars is autowired into FooImpl like this:

@Component
public class FooImpl {
  @Inject
  private Set<Bar> bars;

In a standalone application, Spring instantiates the Bar instances, instantiates the FooImpl instances, and then autowires FooImpl.bars with the set of Bars. It works.

Now I'm running the same Spring configuration in a webapp inside Tomcat. FooLibrary.jar is inside WEB-INF/lib, and everything continues to work as outlined above.

The problem is that the web app automatically compiles somes classes using JavaCompiler, which can't find its dependencies for dynamically compiling unless I place that library on the startup Tomcat path. The minute I add FooLibrary.jar to the Tomcat classpath (e.g. in in the launch configuration of Tomcat inside Eclipse, or I presume startup.sh or setclasspath.bat if running Tomcat standalone), autowire stops working.

That is, when my webapp starts up, Spring creates all the Bar instances, then instantiates FooImpl, but never autowires the set of Bars into FooImpl.bars. Any idea why?

(Does it have something to do with the Spring ContextLoaderListener being started from the webapp classloader, but the FooImpl and Bar instances coming from the Tomcat classloader, I wonder?)

回答1:

Autowiring can fail due to incompatible types (e.g. classes loaded in multiple classloaders).

Since you already place the JAR in tomcat's boot classpath, it must be visible to the webapp as well without you having to place the JAR in WEB-INF/lib.

You can make the dependency scope provided to not have Maven place it in WEB-INF/lib.

来源：https://stackoverflow.com/questions/17029828/spring-autowire-stops-working-for-classes-on-the-tomcat-classpath