This document will give you an overview of how to work with your Java project using the Java Dependency Viewer as well as the Syntax Mode which works best for reading and navigating through source files even without a project structure.
If you run into any issues when using the features below, you can contact us by clicking the Report an issue button below.
Reading and navigating through source code is a common use for a lightweight editor. When developers use VS Code to open a Java source file/folder that doesn't involve a project system (such as drag and drop some Java files into VS Code), it's annoying to see semantic errors reported when the source cannot be resolved to a project. With Syntax Mode, you'll be able to read source code more efficiently with the help of Code Navigation (between your sources and JDK), Outline as well as Javadoc features. Syntax errors are also reported so you can fix them right away.
Usually you won't even know Syntax Mode is on, but you can configure it. Go to Problems panel, and look for the warning File xxx is non-project file, only syntax errors are reported, which means you are in Syntax Mode. If you want to see all the type errors and get full support, right-click on this warning and switch out of Syntax Mode through the context menu. See the screenshots below.
The project mode will provide you full support for standalone Java files. It's also easy to turn back to Syntax Mode for either a single file or any non-project files with the Only report syntax errors for actions.
You can also configure your editor to control whether to enable syntax mode. The configuration is java.server.launchMode, below are the accepted values:
Hybrid (default) - Provides full features with better responsiveness. It starts a standard language server and a secondary syntax server. The syntax server provides syntax features until the standard server is ready. The syntax server will be shutdown automatically after the standard server up and running.Standard - Provides full features such as IntelliSense, refactoring, building, Maven/Gradle support etc. With this option, you will wait until the full server is up for all features.LightWeight - Starts a syntax server with lower start-up cost. Only provides syntax features such as outline, navigation, Javadoc, syntax errors. The lightweight mode won't load third party extensions, such as Java test runner, Java debugger, etc. This mode consumes the least resources but won't provide key features such as IntelliSense.Project Management in Visual Studio Code is provided by the Java Dependency Viewer extension. This extension has many features including creating projects as well as viewing the package structure of the project and its dependencies.
Install the Java Dependency Viewer
In addition to creating a project through Maven Archetype, you can also use the following command to create a simple Java project: Java: Create Java Project from the Command Palette.
If you're creating a Spring Boot project, you can also use the Spring Initializr extension, see Spring Boot in Visual Studio Code.
The extension also has a hierarchy view of your project and dependencies, which supplements the file view and outline provided by Visual Studio Code, so you don't need to expand multiple subfolders to just view your Java package.
Visual Studio Code also supports Java files without a project system. The solution is folder-based, so you can open a source folder with Visual Studio Code. After switching from Syntax Mode to Project Mode (by selecting the Report compilation errors... Quick Fix), all the Java files within the folder will be properly compiled with all language features available. You can also run and debug standalone files.
If you have multiple subfolders that have source code for your project, you can easily add these folders to source path, then all the code inside will be correctly compiled.
If you're just starting to learn Java and don't know what Maven or Gradle are, the Java extension lets you work with JAR files directly without any build tools through the JAVA DEPENDENCIES view.
You can use the Java Dependency Viewer to add any JAR file to your project. Go to the JAVA DEPENDENCIE view, find the Referenced Libraries node, and click the + button to add a JAR file:
The other easy way to bring additional JAR files as dependencies is to create a lib/ folder in the root directory of the standalone files and place your JAR files there. Source for foo.jar is automatically detected if there is a foo-sources.jar in the lib/ folder.
Behind the scene, there's a setting java.project.referencedLibaries in settings.json. Below are details on how to customize this setting.
Include libraries
The libraries to reference are described using a set of glob patterns.
For example:
"java.project.referencedLibraries": [
"library/**/*.jar",
"/home/username/lib/foo.jar"
]The settings above will add all .jar files in workspace's library folder along with foo.jar from a specified absolute path to the project's external dependencies.
The referenced libraries are then watched by VS Code, and the project will be refreshed if there is a change to any of these dependent files.
By default, VS Code will reference all JAR files in workspace's lib directory using the glob pattern lib/**/*.jar.
Exclude some libraries
If you want to exclude some libraries from the project, you can expand java.project.referencedLibraries to use include/exclude fields and add an exclude glob pattern:
"java.project.referencedLibraries": {
"include": [
"library/**/*.jar",
"/home/username/lib/foo.jar"
],
"exclude": [
"library/sources/**"
]
}In the example above, any binary JAR files in the library/sources folder are ignored as the project's external dependencies.
Attach source jars
By default, a referenced {binary}.jar will try to search {binary}-sources.jar under the same directory, and attach it as source if one match is found.
If you want to manually specify a JAR file as a source attachment, you can provide a key-value map in the sources field:
"java.project.referencedLibraries": {
"include": [
"library/**/*.jar",
"/home/username/lib/foo.jar"
],
"exclude": [
"library/sources/**"
],
"sources": {
"library/bar.jar": "library/sources/bar-src.jar"
}
}In this way, bar-src.jar is attached to bar.jar as its source.
In case VS Code throws an error for a classpath issue, try setting your classpath manually by either setting the CLASSPATH environment variable or editing the .classpath file with the path to the JAR file:
<classpathentry kind="lib" path="lib/log4j.jar"/>In some rare cases, you may need to clean the Java workspace by executing the Java: Clean the java language server workspace command from the Command Palette (⇧�P (Windows, Linux Ctrl+Shift+P)) to let the language server rebuild your dependencies.
As Java evolves, Java developers sometimes need to deal with multiple Java runtimes. The Java extension supports preference mapping through the java.configuration.runtimes array for Java execution environments. VS Code will detect the runtime required for your project and choose the appropriate one configured.
"java.configuration.runtimes": [
{
"name": "JavaSE-1.8",
"path": "/usr/local/jdk1.8.0_201"
},
{
"name": "JavaSE-11",
"path": "/usr/local/jdk-11.0.3",
"sources" : "/usr/local/jdk-11.0.3/lib/src.zip",
"javadoc" : "https://docs.oracle.com/en/java/javase/11/docs/api",
"default": true
},
{
"name": "JavaSE-12",
"path": "/usr/local/jdk-12.0.2"
},
{
"name": "JavaSE-13",
"path": "/usr/local/jdk-13"
}
]Runtime names must be one of: "J2SE-1.5", "JavaSE-1.6", "JavaSE-1.7", "JavaSE-1.8", "JavaSE-9", "JavaSE-10", "JavaSE-11", "JavaSE-12", "JavaSE-13", "JavaSE-14". We will update the list with each supported release of the JDK.
When you edit Java source code in Visual Studio Code, the Java language server is building your workspace to provide you with the necessary language features. You can see the detailed build task status and watch what is happening behind the scene by clicking the language server Status bar icon in the lower right.
Visit the GitHub Repo of the Maven extension for additional configurations and a troubleshooting guide.
In addition to Maven, there's also a Bazel extension if you use Bazel to build and test your project.
Read on to find out more about: