[JAVA] How to add a classpath in Spring Boot

Last time, when I was investigating MessageSource related, I needed to put the property file that manages the message outside the Spring Boot project. Reload Spring MessageSource

At that time, when I investigated how to add a classpath with Spring Boot, there were several methods, so I will summarize them.

The settings may differ depending on the startup method, and there may be several setting methods.

environment

• Spring Boot 2.0.6.RELEASE

When booting with mvn spring-boot: run

When starting an application using Spring Boot Maven Plugin. You can add it in one of the following ways.

Specify in the startup argument

You can specify multiple paths separated by commas.

mvn spring-boot:run -Dspring-boot.run.folders=[path]

Write in pom.xml

pom.xml

<plugin>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-maven-plugin</artifactId>
    <configuration>
        <folders>
            <folder>[path]</folder>
        </folders>
    </configuration>
</plugin>

For Executable Jar

When creating an Executable Jar and executing it with the java command. By the way, the classpath is not added even if you do the following.

Bad example

java -cp [path] -jar jarFile

The java command ignores -cp if -jar is specified.

Change the Main class

You can add a classpath by using PropertiesLauncher as the Main class.

If you are using Spring Boot Maven Plugin, you can use Properties Launcher by setting layout to ZIP or DIR.

pom.xml

<plugin>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-maven-plugin</artifactId>
    <configuration>
        <layout>ZIP</layout>
    </configuration>
</plugin>

Next, regarding the settings related to the classpath to be added, there are several setting methods. They are listed in descending order of priority.

Specified in system properties

You can add the classpath with -Dloader.path at startup.

java -Dloader.path=[path] -jar jarFile

By the way, I ran it like -Dloader.path = [path] after -jar and it didn't work, so I was worried for a while. The java command must be specified in the orderjava [-options] -jar jarFile [args ...].

Specify with an environment variable

Set to the environment variable LOADER_PATH. You can start it by using the java command normally.

windows

set LOADER_PATH=[path]

linux

export LOADER_PATH=[path]

Specify in the property file

Place the configuration file with the file name loader.properties directly under resources. This is also OK if you use the java command normally to start it.

loader.properties

loader.path=[path]

The file name and location can be changed by setting.

Specify in the manifest file

You can add the classpath by specifying Loader-Path in the manifest file. Start with the java command normally.

If you use Maven Jar Plugin, you can set as follows.

pom.xml

<plugin>
  <groupId>org.apache.maven.plugins</groupId>
  <artifactId>maven-jar-plugin</artifactId>
  <configuration>
    <archive>
      <manifestEntries>
        <Loader-Path>[path]</Loader-Path>
      </manifestEntries>
    </archive>
  </configuration>
</plugin>

Summary

There are several ways to use Executable Jar, but I wondered if system properties or environment variables that can be set at startup would be good.

In the case of property files and manifest files, the path is written in solid code, so I feel that it is difficult to do if the settings are different for each environment.

Or you can create a property file for each environment and specify the property file name in the system properties at startup.