This version is still in development and is not considered stable yet. For the latest stable version, please use Spring Boot 3.4.1!

PropertiesLauncher Features

PropertiesLauncher has a few special features that can be enabled with external properties (System properties, environment variables, manifest entries, or loader.properties). The following table describes these properties:

Key Purpose

Key	Purpose
`loader.path`	Comma-separated Classpath, such as `lib,${HOME}/app/lib`. Earlier entries take precedence, like a regular `-classpath` on the `javac` command line.
`loader.home`	Used to resolve relative paths in `loader.path`. For example, given `loader.path=lib`, then `${loader.home}/lib` is a classpath location (along with all jar files in that directory). This property is also used to locate a `loader.properties` file, as in the following example `/opt/app` It defaults to `${user.dir}`.
`loader.args`	Default arguments for the main method (space separated).
`loader.main`	Name of main class to launch (for example, `com.app.Application`).
`loader.config.name`	Name of properties file (for example, `launcher`). It defaults to `loader`.
`loader.config.location`	Path to properties file (for example, `classpath:loader.properties`). It defaults to `loader.properties`.
`loader.system`	Boolean flag to indicate that all properties should be added to System properties. It defaults to `false`.

loader.path

Comma-separated Classpath, such as lib,${HOME}/app/lib. Earlier entries take precedence, like a regular -classpath on the javac command line.

loader.home

Used to resolve relative paths in loader.path. For example, given loader.path=lib, then ${loader.home}/lib is a classpath location (along with all jar files in that directory). This property is also used to locate a loader.properties file, as in the following example /opt/app It defaults to ${user.dir}.

loader.args

Default arguments for the main method (space separated).

loader.main

Name of main class to launch (for example, com.app.Application).

loader.config.name

Name of properties file (for example, launcher). It defaults to loader.

loader.config.location

Path to properties file (for example, classpath:loader.properties). It defaults to loader.properties.

loader.system

Boolean flag to indicate that all properties should be added to System properties. It defaults to false.

When specified as environment variables or manifest entries, the following names should be used:

Key Manifest entry Environment variable

Key	Manifest entry	Environment variable
`loader.path`	`Loader-Path`	`LOADER_PATH`
`loader.home`	`Loader-Home`	`LOADER_HOME`
`loader.args`	`Loader-Args`	`LOADER_ARGS`
`loader.main`	`Start-Class`	`LOADER_MAIN`
`loader.config.location`	`Loader-Config-Location`	`LOADER_CONFIG_LOCATION`
`loader.system`	`Loader-System`	`LOADER_SYSTEM`

loader.path

Loader-Path

LOADER_PATH

loader.home

Loader-Home

LOADER_HOME

loader.args

Loader-Args

LOADER_ARGS

loader.main

Start-Class

LOADER_MAIN

loader.config.location

Loader-Config-Location

LOADER_CONFIG_LOCATION

loader.system

Loader-System

LOADER_SYSTEM

Build plugins automatically move the Main-Class attribute to Start-Class when the uber jar is built. If you use that, specify the name of the class to launch by using the Main-Class attribute and leaving out Start-Class.

The following rules apply to working with PropertiesLauncher:

loader.properties is searched for in loader.home, then in the root of the classpath, and then in classpath:/BOOT-INF/classes. The first location where a file with that name exists is used.
loader.home is the directory location of an additional properties file (overriding the default) only when loader.config.location is not specified.
loader.path can contain directories (which are scanned recursively for jar and zip files), archive paths, a directory within an archive that is scanned for jar files (for example, dependencies.jar!/lib), or wildcard patterns (for the default JVM behavior). Archive paths can be relative to loader.home or anywhere in the file system with a jar:file: prefix.
loader.path (if empty) defaults to BOOT-INF/lib (meaning a local directory or a nested one if running from an archive). Because of this, PropertiesLauncher behaves the same as JarLauncher when no additional configuration is provided.
loader.path can not be used to configure the location of loader.properties (the classpath used to search for the latter is the JVM classpath when PropertiesLauncher is launched).
Placeholder replacement is done from System and environment variables plus the properties file itself on all values before use.
The search order for properties (where it makes sense to look in more than one place) is environment variables, system properties, loader.properties, the exploded archive manifest, and the archive manifest.