Eclipse Java EE IDE 创建 Dynamic Web project问题

Eclipse Java EE IDE for Web Developers 创建的 Dynamic Web project 编译后的class文件默认存放路径问题，默认存放路径是build/classes导致应用部署后，Tomcat 抛出异常：

The value for the useBean class attribute XXX is invalid

Java Servlet 3.0 Specification（java Servlet 3.0 规范是这样描述的）

10.5 Directory Structure
A Web application exists as a structured hierarchy of directories. The root of this hierarchy serves as the
document root for files that are part of the application. For
example, for a Web application with the context path /catalog in a Web
container, the index.html file at the base of the Web application
hierarchy or in a JAR file inside WEB-INF/lib that includes the
index.html under META-INF/resources directory can be served to
satisfy a request from /catalog/index.html. If an index.html is
present both in the root context and in the META-INF/resources
directory of a JAR file in the WEB-INF/lib directory of the
application, then the file that is available in the root context MUST
be used. The rules for matching URLs to context path are laid out in
Chapter 12, “Mapping Requests to Servlets”. Since the context path of
an application determines the URL namespace of the contents of the
Web application, Web containers must reject Web applications defining
a context path that could cause potential conflicts in this URL
namespace. This may occur, for example, by attempting to deploy a
second Web application with the same context path. Since requests are
matched to resources in a case-sensitive manner, this determination
of potential conflict must be performed in a case-sensitive manner as
well. A special directory exists within the application hierarchy
named “WEB-INF”. This directory contains all things related to the
application that aren’t in the document root of the application. Most
of the WEB-INF node is not part of the public document tree of the
application. Except for static resources and JSPs packaged in the
META- INF/resources of a JAR file that resides in the WEB-INF/lib
directory, no other files contained in the WEB-INF directory may be
served directly to a client by the container. However, the contents
of the WEB-INF directory are visible to servlet code using the
getResource and getResourceAsStream method calls on the
ServletContext, and may be exposed using the RequestDispatcher calls.
Hence, if the Application Developer needs access, from servlet code,
to application specific configuration information that he does not
wish to be exposed directly to the Web client, he may place it under
this directory. Since requests are matched to resource mappings in a
case-sensitive manner, client requests for ‘/WEB-INF/foo’, ‘/WEb-
iNf/foo’, for example, should not result in contents of the Web
application located under /WEB-INF being returned, nor any form of
directory listing thereof. The contents of the WEB-INF directory are:
■ The /WEB-INF/web.xml deployment descriptor.
■ The /WEB-INF/classes/ directory for servlet and utility classes. The classes in this
directory must be available to the application class loader.
■ The /WEB-INF/lib/*.jar area for Java ARchive files. These files contain
servlets, beans, static resources and JSPs packaged in a JAR file and
other utility classes useful to the Web application. The Web
application class loader must be able to load classes from any of
these archive files. The Web application class loader must load
classes from the WEB-INF/classes directory first, and then from
library JARs in the WEB-INF/lib directory. Also, except for the case
where static resources are packaged in JAR files, any requests from
the client to access the resources in WEB-INF/ directory must be
returned with a SC_NOT_FOUND(404) response.

规范的定义：服务器的class loader类加载器默认加载 /WEB-INF/classes目录下的 .class文件 *

**1** 在创建 Dynamic Web project 时，就可以设置*.class文件的输出存放目录：

File>new > Dynamic Web project > next > 在default output folder地方的"build/classes"改成"WEB-INF\classes” > finish就可以了

**2** 如果在创建的时候忘记更改的话：

可以右击项目>build path > configure build path > 选择 source选项，将default output folder地方的"build/classes"改成"WebContent/WEB-INF/classes” > finish就可以了