feat: multimodule maven support

core/__snapshots__/TestGenerateBuildPlanForExamples_java-maven-multimodule_1.snap.json

@@ -0,0 +1,125 @@
+{
+ "caches": {
+  "maven": {
+   "directory": ".m2/repository",
+   "type": "shared"
+  }
+ },
+ "deploy": {
+  "base": {
+   "image": "ghcr.io/railwayapp/railpack-runtime:latest"
+  },
+  "inputs": [
+   {
+    "include": [
+     "/mise/shims",
+     "/mise/installs",
+     "/usr/local/bin/mise",
+     "/etc/mise/config.toml",
+     "/root/.local/state/mise"
+    ],
+    "step": "packages:mise:runtime"
+   },
+   {
+    "include": [
+     "."
+    ],
+    "step": "build"
+   }
+  ],
+  "startCommand": "java  $JAVA_OPTS -jar $(find */target -name '*-jar-with-dependencies.jar' -o -name '*-spring-boot*.jar' | head -1)"
+ },
+ "steps": [
+  {
+   "assets": {
+    "mise.toml": "[mise.toml]"
+   },
+   "commands": [
+    {
+     "path": "/mise/shims"
+    },
+    {
+     "customName": "create mise config",
+     "name": "mise.toml",
+     "path": "/etc/mise/config.toml"
+    },
+    {
+     "cmd": "sh -c 'mise trust -a \u0026\u0026 mise install'",
+     "customName": "install mise packages: java, maven"
+    }
+   ],
+   "inputs": [
+    {
+     "image": "ghcr.io/railwayapp/railpack-builder:latest"
+    }
+   ],
+   "name": "packages:mise",
+   "variables": {
+    "MISE_CACHE_DIR": "/mise/cache",
+    "MISE_CONFIG_DIR": "/mise",
+    "MISE_DATA_DIR": "/mise",
+    "MISE_INSTALLS_DIR": "/mise/installs",
+    "MISE_NODE_VERIFY": "false",
+    "MISE_SHIMS_DIR": "/mise/shims"
+   }
+  },
+  {
+   "caches": [
+    "maven"
+   ],
+   "commands": [
+    {
+     "cmd": "mvn -DoutputFile=target/mvn-dependency-list.log -B -DskipTests clean dependency:list install -Pproduction"
+    }
+   ],
+   "inputs": [
+    {
+     "step": "packages:mise"
+    },
+    {
+     "include": [
+      "."
+     ],
+     "local": true
+    }
+   ],
+   "name": "build",
+   "secrets": [
+    "*"
+   ]
+  },
+  {
+   "assets": {
+    "mise.toml": "[mise.toml]"
+   },
+   "commands": [
+    {
+     "path": "/mise/shims"
+    },
+    {
+     "customName": "create mise config",
+     "name": "mise.toml",
+     "path": "/etc/mise/config.toml"
+    },
+    {
+     "cmd": "sh -c 'mise trust -a \u0026\u0026 mise install'",
+     "customName": "install mise packages: java"
+    }
+   ],
+   "inputs": [
+    {
+     "image": "ghcr.io/railwayapp/railpack-builder:latest"
+    }
+   ],
+   "name": "packages:mise:runtime",
+   "variables": {
+    "MISE_CACHE_DIR": "/mise/cache",
+    "MISE_CONFIG_DIR": "/mise",
+    "MISE_DATA_DIR": "/mise",
+    "MISE_INSTALLS_DIR": "/mise/installs",
+    "MISE_NODE_VERIFY": "false",
+    "MISE_SHIMS_DIR": "/mise/shims"
+   }
+  }
+ ]
+}

core/providers/java/java.go

@@ -62,6 +62,9 @@ func (p *JavaProvider) Plan(ctx *generate.GenerateContext) error {
 	outPath := "target/."
 	if ctx.App.HasMatch("**/build/libs/*.jar") || p.usesGradle(ctx) {
 		outPath = "."
+	} else if p.isMultimoduleMaven(ctx) {
+		outPath = "."
+		ctx.Logger.LogWarn("Multi-module Maven project detected. If the build fails to find the correct JAR, specify a custom start command.")
 	}
 
 	ctx.Deploy.AddInputs([]plan.Layer{
@@ -81,9 +84,14 @@ func (p *JavaProvider) Plan(ctx *generate.GenerateContext) error {
 func (p *JavaProvider) getStartCmd(ctx *generate.GenerateContext) string {
 	if p.usesGradle(ctx) {
 		buildGradle := p.readBuildGradle(ctx)
+		// TODO this seems like a hack? Why are we doing it like this? Let's make sure this is tested and then we can refactor
 		return fmt.Sprintf("java $JAVA_OPTS -jar %s $(ls -1 */build/libs/*jar | grep -v plain)", getGradlePortConfig(buildGradle))
-	} else if ctx.App.HasMatch("pom.xml") {
-		return fmt.Sprintf("java %s $JAVA_OPTS -jar target/*jar", getMavenPortConfig(ctx))
+	} else if ctx.App.HasFile("pom.xml") {
+		portConfig := getMavenPortConfig(ctx)
+		if p.isMultimoduleMaven(ctx) {
+			return fmt.Sprintf("java %s $JAVA_OPTS -jar $(find */target -name '*-jar-with-dependencies.jar' -o -name '*-spring-boot*.jar' | head -1)", portConfig)
+		}
+		return fmt.Sprintf("java %s $JAVA_OPTS -jar target/*jar", portConfig)
 	} else {
 		return "java $JAVA_OPTS -jar target/*jar"
 	}

core/providers/java/maven.go

@@ -8,6 +8,16 @@ import (
 
 const MAVEN_CACHE_KEY = "maven"
 
+// isMultimoduleMaven detects if this is a multi-module Maven project where JARs
+// are built in subdirectories (e.g., app/target/*.jar) rather than at the root.
+func (p *JavaProvider) isMultimoduleMaven(ctx *generate.GenerateContext) bool {
+	pomFile, err := ctx.App.ReadFile("pom.xml")
+	if err != nil {
+		return false
+	}
+	return strings.Contains(pomFile, "<modules>")
+}
+
 func (p *JavaProvider) getMavenExe(ctx *generate.GenerateContext) string {
 	if ctx.App.HasMatch("mvnw") && ctx.App.HasMatch(".mvn/wrapper/maven-wrapper.properties") {
 		return "./mvnw"

docs/src/content/docs/languages/java.md

@@ -27,3 +27,37 @@ The Java version is determined in the following order:
 | ------------------------- | --------------------------- | ------- |
 | `RAILPACK_JDK_VERSION`    | Override the JDK version    | `17`    |
 | `RAILPACK_GRADLE_VERSION` | Override the Gradle version | `8.5`   |
+
+## Multi-Module Projects
+
+Railpack detects multi-module Maven and Gradle projects (identified by
+`<modules>` in the root `pom.xml` or multiple subprojects in Gradle).
+
+For multi-module projects, Railpack finds the JAR to run using this
+heuristic:
+
+1. First, looks for `*-jar-with-dependencies.jar` (Maven Assembly Plugin)
+2. Then, looks for `*-spring-boot*.jar` (Spring Boot Maven Plugin)
+3. Finally, picks the first JAR matching `*/target/*.jar` for Maven or
+   `*/build/libs/*.jar` for Gradle
+
+This heuristic may not work if:
+
+- Your project has multiple executable JARs
+- JARs don't follow standard naming conventions
+- The build produces only thin JARs (without bundled dependencies)
+
+If JAR selection fails, specify a custom start command.
+
+## Custom Start Command
+
+To override the default start command, create a `railpack.json` file in
+your project root:
+
+```json
+{
+  "deploy": {
+    "startCommand": "java -jar server/target/my-app.jar"
+  }
+}
+```

examples/java-maven-multimodule/.gitignore

@@ -0,0 +1,2 @@
+!test/
+target/

examples/java-maven-multimodule/app/pom.xml

@@ -0,0 +1,47 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+  <parent>
+    <groupId>com.railpack</groupId>
+    <artifactId>java-maven-multimodule</artifactId>
+    <version>1.0-SNAPSHOT</version>
+  </parent>
+  <artifactId>java-maven-app</artifactId>
+  <dependencies>
+    <dependency>
+      <groupId>${project.groupId}</groupId>
+      <artifactId>java-maven-lib</artifactId>
+      <version>${project.version}</version>
+    </dependency>
+  </dependencies>
+  <build>
+    <plugins>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-assembly-plugin</artifactId>
+        <executions>
+          <execution>
+            <phase>package</phase>
+            <goals>
+              <goal>single</goal>
+            </goals>
+            <configuration>
+              <archive>
+                <manifest>
+                  <mainClass>
+                    com.railpack.app.App
+                  </mainClass>
+                </manifest>
+              </archive>
+              <descriptorRefs>
+                <descriptorRef>jar-with-dependencies</descriptorRef>
+              </descriptorRefs>
+            </configuration>
+          </execution>
+        </executions>
+      </plugin>
+    </plugins>
+  </build>
+</project>

examples/java-maven-multimodule/app/src/main/java/com/railpack/app/App.java

@@ -0,0 +1,13 @@
+package com.railpack.app;
+
+import com.railpack.lib.Util;
+
+/**
+ * Hello world!
+ */
+public class App {
+
+  public static void main(String[] args) {
+    System.out.println(Util.getMessage());
+  }
+}

examples/java-maven-multimodule/app/src/test/java/com/railpack/app/AppTest.java

@@ -0,0 +1,19 @@
+package com.railpack.app;
+
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import org.junit.jupiter.api.Test;
+
+/**
+ * Unit test for simple App.
+ */
+public class AppTest {
+
+    /**
+     * Rigorous Test :-)
+     */
+    @Test
+    public void shouldAnswerWithTrue() {
+        assertTrue(true);
+    }
+}

examples/java-maven-multimodule/lib/pom.xml

@@ -0,0 +1,11 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+    <parent>
+      <groupId>com.railpack</groupId>
+      <artifactId>java-maven-multimodule</artifactId>
+      <version>1.0-SNAPSHOT</version>
+    </parent>
+    <artifactId>java-maven-lib</artifactId>
+</project>

examples/java-maven-multimodule/lib/src/main/java/lib/Util.java

@@ -0,0 +1,8 @@
+package com.railpack.lib;
+
+public class Util {
+
+  public static String getMessage() {
+    return "Hello Railpack!";
+  }
+}