can codeql analyse java rt.jar source code?

i want to analyse part of jdk source code,so i tried to unzip jdk src.zip,it contains `java.io.*,java.lang.*`

then i create pom.xml and run `codeql database create jdk_src --language=java --command="mvn clean package"`.

`database-create-20200630.203801.550.log` indicate codeql does not find any source code.

```
[2020-06-30 20:38:50] [ERROR] database finalize> No source code was seen during the build.
This can occur if the specified build commands failed to compile or process any code.
- Confirm that there is some source code for the specified language in the project.
- For codebases written in Go, JavaScript, TypeScript, and Python, do not specify
an explicit --command.
- For other languages, the --command must specify a "clean" build which compiles
all the source code files without reusing existing build artefacts.
```