为什么 VSCode 一直打开 *.class 文件而不是 .java 文件？

Question

(I couldn't figure out how to upload my screen capture to stackoverflow. So this is a streamable link: https://streamable.com/0im8tx )

In this video, VSCode opens QueriesController.class as opposed to QueriesController.java when I cmd click into QueriesController .

I have compiled provided the definitions of the jar file in my workspace:

    "settings": {
        "java.project.referencedLibraries": {
            "include": [
                "<path-to-jar-that-contains-QueriesController.jar>",
.... 
            "sources": {
                "<path-to-jar-that-contains-QueriesController.jar>": "/my/local/java/definition/src/folder",

Does anyone know why VSCode is choosing to open the definition as a.class file rather than a.java file?

Answer 1

I use commands to generate a simple jar package and use it in another project. It's true that when we click the class name, .class file is opened instead of .java file:

About how to generate a executable jar package, you can have a look at this reply :

1. Compile.java file and generate.class;

2. Generate manifest and pack them into jar

In general, a JAR (Java ARchive) is a package file format typically used to aggregate many Java class files and associated metadata and resources (text, images, etc.) into one file for distribution.

.java file isn't included in jar packages, and that's why you get.class file opened instead of.java file.

Answer 2

I am not familiar with VSCode but your problem is common across most IDEs.

Usually when a jar is made, it consists of compiled class files rather than original source codes. The reason for this is to run code as efficient and fast as possible and usually people don't want source code in jar because when running they also have to be recompiled again which is a waste of time.

Take a look at this picture. I have just downloaded a jar file from mavenrepository and it downloads the compiled version of jar. The extension is .class

What the IDE does is it tries to decompile the code with a decompiler (In this case as you can see FernFlower decompiler).

However it lacks formatting and in-code documentation the source code (.java) has. Which is why most IDEs offer to download sources. Intellij shows this right on top. Other IDEs may have this setting buried in deep. (You may have to check for yourself)

When you download sources, IDE try to contact the server and download original source code. Probably that would look something like this:

If you look closely you can see name has changed to .java which represents the source code.

Answer 3

VS Code has option under Java Settings, Java Download sources and Maven download sources .

It is not enabled by default. Upon enabling it, VS Code shows the proper source file, although the name appears to be .Class files.(Upon Ctrl + Clicking the symbol, with method implementations, comments, etc.,JavaDoc Comments)

If proper sources are not found in m2 repository, it shows the decompiled class file with stubbed methods. A comment similar to this is shown at the beginning of the file.

// Failed to get sources. Instead, stub sources have been generated by the disassembler.
 // Implementation of methods is unavailable.

In Either of the cases, VS Code shows the maven library files as .Class files in read-only mode. Also, source files are not displayed on the Java Project Explorer.(Although even if it exists in the local.m2 repos).

Hope that helps! Happy Coding!