VS Code support for Java using the javac API

Provides Java support using the javac API. Requires that you have Java 8 installed on your system.

Installation

Install from the VS Code marketplace

Issues

Features

Autocomplete

Go-to-definition

Find symbol

Lint

Type information on hover

Find references

Usage

Using Maven pom.xml

vscode-javac will look for a file named pom.xml in a parent directory of every open .java file. vscode-javac will invoke maven in order to get the build classpath, so you need to be sure mvn is on your system path.

Using javaconfig.json

The presence of a javaconfig.json file indicates that its parent directory is the root of a Java module. javaconfig.json looks like:

{
    "sourcePath": ["relative/path/to/source/root", ...],
    "classPathFile": "file-with-classpath-as-contents.txt",
    "outputDirectory": "relative/path/to/output/root"
}

The classpath is contained in a separate file, in the format entry.jar:another-entry.jar. This file is usually generated by a build tool like maven.

Examples

Maven

pom.xml will be read automatically.

Maven (using javaconfig.json)

You can configure maven to output the current classpath to a file, classpath.txt, where Visual Studio Code will find it.

javaconfig.json

Set the source path, and get the class path from a file:

{
    "sourcePath": ["src/main/java"],
    "classPathFile": "classpath.txt",
    "outputDirectory": "target"
}

pom.xml

Configure maven to output classpath.txt

<project ...>
    ...
    <build>
        ...
        <plugins>
            ...
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-dependency-plugin</artifactId>
                <version>2.9</version>
                <executions>
                    <execution>
                        <id>build-classpath</id>
                        <phase>generate-sources</phase>
                        <goals>
                            <goal>build-classpath</goal>
                        </goals>
                    </execution>
                </executions>
                <configuration>
                    <outputFile>classpath.txt</outputFile>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

.gitignore

Ignore classpath.txt, since it will be different on every host

classpath.txt
...

Gradle

Add this to your build.gradle:

task vscodeClasspathFile {
    description 'Generates classpath file for the Visual Studio Code java plugin'
    ext.destFile = file("$buildDir/classpath.txt")
    outputs.file destFile
    doLast {
        def classpathString = configurations.compile.collect{ it.absolutePath }.join(':')
        assert destFile.parentFile.mkdir()
        destFile.text = classpathString
    }
}

task vscodeJavaconfigFile(dependsOn: vscodeClasspathFile) {
    description 'Generates javaconfig.json file for the Visual Studio Code java plugin'

    def relativePath = { File f ->
        f.absolutePath - "${project.rootDir.absolutePath}/"
    }
    ext.destFile = file("javaconfig.json")
    ext.config = [
        sourcePath: sourceSets.collect{ it.java.srcDirs }.flatten().collect{ relativePath(it) },
        classPathFile: relativePath(tasks.getByPath(':vscodeClasspathFile').outputs.files.singleFile),
        outputDirectory: relativePath(new File(buildDir, 'vscode-classes'))
    ]
    doLast {
        def jsonContent = groovy.json.JsonOutput.toJson(ext.config)
        destFile.text = groovy.json.JsonOutput.prettyPrint(jsonContent)
    }
}

task vscode(dependsOn: vscodeJavaconfigFile) {
    description 'Generates config files for the Visual Studio Code java plugin'
    group 'vscode'
}

Then run gradlew vscode. This will generate

• javaconfig.json
• build/classpath.txt

Directory structure

Java service process

A java process that does the hard work of parsing and analyzing .java source files.

pom.xml (maven project file)
src/ (java sources)
repo/ (tools.jar packaged in a local maven repo)
target/ (compiled java .class files, .jar archives)
target/fat-jar.jar (single jar that needs to be distributed with extension)

Typescript Visual Studio Code extension

"Glue code" that launches the external java process and connects to it using vscode-languageclient.

package.json (node package file)
tsconfig.json (typescript compilation configuration file)
tsd.json (project file for tsd, a type definitions manager)
lib/ (typescript sources)
out/ (compiled javascript)

Design

This extension consists of an external java process, which communicates with vscode using the language server protocol.

Java service process

The java service process uses the implementation of the Java compiler in tools.jar, which is a part of the JDK. When VS Code needs to lint a file, perform autocomplete, or some other task that requires Java code insight, the java service process invokes the Java compiler programatically, then intercepts the data structures the Java compiler uses to represent source trees and types.

Incremental updates

The Java compiler isn't designed for incremental parsing and analysis. However, it is extremely fast, so recompiling a single file gives good performance, as long as we don't also recompile all of its dependencies. We accomplish this by maintaining a single copy of the Java compiler in memory at all times. When we want to recompile a file, we clear that one file from the internal caches of the Java compiler, and then rerun the compiler.

Multiple javaconfig.json

If you have multiple javaconfig.json files in different subdirectories of your project, the parent directory of each javaconfig.json will be treated as a separate java root.

Logs

The java service process will output a log file with a name like 'javac-services.0.log' in your project directory.

Contributing

If you have npm and maven installed, you should be able to install locally using

npm install -g vsce
npm install
./scripts/install.sh