eclipse无法创建src/main/java目录，提示The folder is already a source folder.

场景：构建cas项目时，目录结构缺少src/main/java

手动创建报错如下：

The folder is already a source folder.这个文件夹已经是一个源文件夹了。

eclipse无法创建src/main/java目录，提示The folder is already a source folder.

从java build path中可以看到，src/main/java显示为missing缺失。选中remove掉，重新创建就不会报错了

eclipse无法创建src/main/java目录，提示The folder is already a source folder.

重新创建后，需要将src/main/java设置为代码文件根目录。打开navigator模式

eclipse无法创建src/main/java目录，提示The folder is already a source folder.

打开 .classpath文件，将圈选配置修改为：<classpathentry kind="src" output="target/classes" path="src/main/java"/>

eclipse无法创建src/main/java目录，提示The folder is already a source folder.