OpenJDK 11 javadoc not returned on hover

I am running Debian testing with OpenJDK 11. I am using Neovim v0.3.4. Lately, jdt.ls has not been returning javadoc from the OpenJDK 11 doc package in hover responses. For example, if I hover on the keyword String, I do not get the javadoc for String. Instead I get this: I had it working with snapshot jdt-language-server-0.36.0-201903201910 and neoclide/coc-java as my client for a while and it just suddenly stopped working. The problem seemed to be that I had set JAVA_HOME for maven and I was able to get snapshot jdt-language-server-0.36.1-201904020132 to send javadoc by explicitly configuring the path to the jdk in coc’s settings (even though it was the same path as JAVA_HOME). However, jdt.ls has stopped sending the jdk javadoc again and I have not been able to get it to work again. I have tried the most recent snapshot (jdt-language-server-0.37.0-201904162228) but it does not send the jdk javadoc either. To rule out coc as the problem, I also tried using prabirshrestha/vim-lsp as my client and I still had the same problem. Here is a trace I get from coc:

[Trace - 3:45:08 PM] Sending request 'textDocument/hover - (5)'.
Params: {
    "textDocument": {
        "uri": "file:///home/user/udemy/maven/mb2g-lombok/src/main/java/guru/springframework/model/User.java"
    },
    "position": {
        "line": 12,
        "character": 14
    }
}


[Trace - 3:45:08 PM] Received response 'textDocument/hover - (5)' in 56ms.
Result: {
    "contents": {
        "language": "java",
        "value": "java.lang.String"
    }
}

The bug report I made to neoclide/coc-java concerning this issue can be found here. I have closed that issue since this seems to be a problem between jdt.ls and OpenJDK 11 on Debian and not an issue with my lsp client.

[Yanpas]

Same issue in ubuntu. Fixes with sudo ln -fsr /usr/lib/jvm/openjdk-11/lib/src.zip /usr/lib/jvm/java-11-openjdk-amd64/src.zip. Need to install openjdk-11-source as well

[STimur]

Same issue in ubuntu. Fixes with sudo ln -fsr /usr/lib/jvm/openjdk-11/lib/src.zip /usr/lib/jvm/java-11-openjdk-amd64/src.zip. Need to install openjdk-11-source as well

don’t fully understand why it works, but this command helped me resolve same issue in IntelliJ IDEA 2019.3.1 (Ultimate Edition) on ubuntu 18.04.3 LTS - i had no documentation for Java SE 11 when pressing Ctrl-Q

Thanks a lot!