Hello,

I developed a Java library and I am trying to import it into my 1.20.1 Minecraft mod using Forge 47.2.0. I added my libs folder as a flatDir repository using the following code:

repositories
{
     flatDir
     {
         dir 'src/main/resources/libs'
     }
}

and I added my library (mc-astar-1.1.jar) to the classpath by adding

minecraftLibrary "blank:mc-astar:1.1"

to my dependencies block, which should be enough for properly importing the library, according to the docs. However, the library only seems to be added to the compiletime classpath, but not to the runtime classpath as the Java compiler doesn't report any compile-time errors and a NoClassDefFoundError is thrown as soon as I try to access any classes contained in the library. To ensure that my library is not the issue I tried to import the Java Discord API as a jar library as well and it didn't work either.

I already spent a few hours solving this problem, so I will greatly appreciate any hint about what detail I am missing here.

Thank you!

You must use implementation for mods or files to include a mods as dependecy.

See: https://docs.gradle.org/current/userguide/declaring_dependencies.html

Thank you, that source improved my understanding on gradle dependencies, but unfortunately it didn't fix my problem. I tried to add the dependency to the "implementation" configuration, but the library is still not present at runtime. Just to test, I also tried to explicitly add the dependency to the "runtimeOnly" configuration as well, which didn't change anything either.

Plese post full build.gradle

Sure, though it's pretty much the default one from the Forge MDK

plugins {
    id 'eclipse'
    id 'idea'
    id 'maven-publish'
    id 'net.minecraftforge.gradle' version '[6.0,6.2)'
}

version = mod_version
group = mod_group_id

base {
    archivesName = mod_id
}

java.toolchain.languageVersion = JavaLanguageVersion.of(17)

println "Java: ${System.getProperty 'java.version'}, JVM: ${System.getProperty 'java.vm.version'} (${System.getProperty 'java.vendor'}), Arch: ${System.getProperty 'os.arch'}"
minecraft {
    mappings channel: mapping_channel, version: mapping_version
    copyIdeResources = true
    runs {
        configureEach {
            workingDirectory project.file('run')
            property 'forge.logging.markers', 'REGISTRIES'
            property 'forge.logging.console.level', 'debug'

            mods {
                "mcastartest" {
                    source sourceSets.main
                }
            }
        }

        client {
            property 'forge.enabledGameTestNamespaces', mod_id
        }
        server {
            property 'forge.enabledGameTestNamespaces', mod_id
            args '--nogui'
        }
        gameTestServer {
            property 'forge.enabledGameTestNamespaces', mod_id
        }

        data {
            workingDirectory project.file('run-data')
            args '--mod', mod_id, '--all', '--output', file('src/generated/resources/'), '--existing', file('src/main/resources/')
        }
    }
}

sourceSets.main.resources { srcDir 'src/generated/resources' }

repositories
{
     flatDir
     {
         dir 'src/main/resources/libs'
     }
}

dependencies
{
    minecraft "net.minecraftforge:forge:${minecraft_version}-${forge_version}"

    implementation "blank:mc-astar:1.1"
}

tasks.named('processResources', ProcessResources).configure {
    var replaceProperties = [
            minecraft_version: minecraft_version, minecraft_version_range: minecraft_version_range,
            forge_version: forge_version, forge_version_range: forge_version_range,
            loader_version_range: loader_version_range,
            mod_id: mod_id, mod_name: mod_name, mod_license: mod_license, mod_version: mod_version,
            mod_authors: mod_authors, mod_description: mod_description,
    ]
    inputs.properties replaceProperties

    filesMatching(['META-INF/mods.toml', 'pack.mcmeta']) {
        expand replaceProperties + [project: project]
    }
}

tasks.named('jar', Jar).configure {
    manifest {
        attributes([
                'Specification-Title'     : mod_id,
                'Specification-Vendor'    : mod_authors,
                'Specification-Version'   : '1',
                'Implementation-Title'    : project.name,
                'Implementation-Version'  : project.jar.archiveVersion,
                'Implementation-Vendor'   : mod_authors,
                'Implementation-Timestamp': new Date().format("yyyy-MM-dd'T'HH:mm:ssZ")
        ])
    }
    
    finalizedBy 'reobfJar'
}

publishing {
    publications {
        register('mavenJava', MavenPublication) {
            artifact jar
        }
    }
    repositories {
        maven {
            url "file://${project.projectDir}/mcmodsrepo"
        }
    }
}

tasks.withType(JavaCompile).configureEach {
    options.encoding = 'UTF-8'
}

 

Where is the dependency source of "blank:mc-astar:1.1" is it on cursemaven, a file, or ...?

It's the release from my GitHub repo. I renamed it to "mc-astar-1.1.jar" for testing and moved it to the "src/main/resources/libs" folder of my mod project.

If it's a file, you have to use:

dependencies {
    implementation files("<file_name>")
}

 

I tried the following now

implementation files("src/main/resources/libs/mc-astar-1.1.jar")

and it throws still the same NoClassDefFoundError. Also tried it again with the JDA just to be sure my API is not the problem and it also didn't work.

Just the file name, you already told gradle where to find the .jar file:

22 hours ago, Flopticode said:

repositories
{
     flatDir
     {
         dir 'src/main/resources/libs'
     }
}

 

That's what I thought too at first, but when I tried just the filename, the project failed to compile. Then I looked up the classpath generated by gradle and saw that it added "mc-astar-1.1.jar" at the project's root directory, not in "src/main/resources/libs" as I would have expected.

Post the error you get when you compile the project 

I don't get a specific error from gradle, it returns "BUILD SUCCESSFUL". However, eclipse shows an entry

mc-astar-1.1.jar - P:\Java\MinecraftModding\1.20.1\MCAStarMod (missing)

in the classpath window after refreshing the gradle project. This obviously implies several "The import mc_astar_java cannot be resolved" compile errors everywhere I use the library's packages in the Java code.

On the other hand, if I add the path in the "implementation" statement in the gradle file, the classpath shows

mc-astar-1.1.jar - P:\Java\MinecraftModding\1.20.1\MCAStarMod\src\main\resources\libs

and I get no compile errors, meaning it should at least find the library (right?)

Edited November 20, 20231 yr by Flopticode

2 hours ago, Flopticode said:

and I get no compile errors, meaning it should at least find the library (right?)

Could you use the mod during develop in this case?

It's the same situation as in this post from before:

On 11/19/2023 at 8:38 PM, Flopticode said:

I tried the following now

implementation files("src/main/resources/libs/mc-astar-1.1.jar")

and it throws still the same NoClassDefFoundError. Also tried it again with the JDA just to be sure my API is not the problem and it also didn't work.

So I guess in theory I could export my mod to use it in-game like an end-user would, but I don't think I can properly develop a mod without any debugging / testing tools from the IDE.

First of all i do not recommend you to include you mod as a jar file, it's recommend to publish it to a local maven repository which you then include in your other projects.

Secondly, I don't recommend you use native code with Minecraft. I have already tried this but have found that this can lead to terrible errors.

I have tested the whole thing myself in my IDE and it works for me in IntelliJ:

repositories {
  // ...
  flatDir {
    dirs("libs") // jar file must be in "<project_root>/libs"
  }
  // ...
}

dependencies {
  // ...
  implementation fg.deobf("blank:MC-AStar:1.20:1.0") // File pattern must be <name>-<mc_version>-<dependency_version>
  // ...
}

Edited November 21, 20231 yr by Luis_ST

You're right, I have now set up a local maven repo and published my library to it. That should make things way easier in the future.

I think in my case native code is a good option because the dll does not interact with Minecraft directly at all, it is always controlled through a mod. I'm aware of the potential problems (memory leaks, segfaults, hardware dependencies, ...) that native code can cause, but I am very experienced in C++ and always double check these errors in my code.

Is it possible that you tested this with a mod, not a library? afaik fg.deobf is just for deobfuscating mods so that they can run in development environments. Also my library has no MC version as it is completely independent from Minecraft (just features pathfinding functions for an abstract world). I tested your gradle script anyway (that was before I set up the Maven repo btw, so this still refers to the jar inside the 'libs' folder) and it didn't seem to work (gradle throws an exception that the artifact was not found, probably due to the fact that fg.deobf can't handle that dependency as it is not a mod?).

After I set up the maven repo, I added it to my gradle file like this

repositories
{
     maven {
     	url "P:/repos/maven"
     }
}

and I retested some of the previous options, hoping that it just didn't work for flat dirs (obviously I tried just one of these at a time):

minecraftLibrary "flopticode:mc-astar:1.1"
implementation "flopticode:mc-astar:1.1"
minecraftLibrary fg.deobf("flopticode:mc-astar:1.1")
implementation fg.deobf("flopticode:mc-astar:1.1")

All of these result in the same NoClassDefFoundError. At this point I am completely confused why it doesn't work as I did exactly what this entry from the Forge Documentation says.

Please post a your full build.gradle file

Quote

plugins {
    id 'eclipse'
    id 'idea'
    id 'maven-publish'
    id 'net.minecraftforge.gradle' version '[6.0,6.2)'
}

version = mod_version
group = mod_group_id

base {
    archivesName = mod_id
}

java.toolchain.languageVersion = JavaLanguageVersion.of(17)

println "Java: ${System.getProperty 'java.version'}, JVM: ${System.getProperty 'java.vm.version'} (${System.getProperty 'java.vendor'}), Arch: ${System.getProperty 'os.arch'}"
minecraft {
    mappings channel: mapping_channel, version: mapping_version
    copyIdeResources = true
    runs {
        configureEach {
            workingDirectory project.file('run')
            property 'forge.logging.markers', 'REGISTRIES'
            property 'forge.logging.console.level', 'debug'

            mods {
                "mcastartest" {
                    source sourceSets.main
                }
            }
        }

        client {
            property 'forge.enabledGameTestNamespaces', mod_id
        }
        server {
            property 'forge.enabledGameTestNamespaces', mod_id
            args '--nogui'
        }
        gameTestServer {
            property 'forge.enabledGameTestNamespaces', mod_id
        }

        data {
            workingDirectory project.file('run-data')
            args '--mod', mod_id, '--all', '--output', file('src/generated/resources/'), '--existing', file('src/main/resources/')
        }
    }
}

sourceSets.main.resources { srcDir 'src/generated/resources' }

repositories
{
     maven {
     	url "P:/repos/maven"
     }
}

dependencies
{
    minecraft "net.minecraftforge:forge:${minecraft_version}-${forge_version}"
    minecraftLibrary "flopticode:mc-astar:1.1"
}

tasks.named('processResources', ProcessResources).configure {
    var replaceProperties = [
            minecraft_version: minecraft_version, minecraft_version_range: minecraft_version_range,
            forge_version: forge_version, forge_version_range: forge_version_range,
            loader_version_range: loader_version_range,
            mod_id: mod_id, mod_name: mod_name, mod_license: mod_license, mod_version: mod_version,
            mod_authors: mod_authors, mod_description: mod_description,
    ]
    inputs.properties replaceProperties

    filesMatching(['META-INF/mods.toml', 'pack.mcmeta']) {
        expand replaceProperties + [project: project]
    }
}

tasks.named('jar', Jar).configure {
    manifest {
        attributes([
                'Specification-Title'     : mod_id,
                'Specification-Vendor'    : mod_authors,
                'Specification-Version'   : '1',
                'Implementation-Title'    : project.name,
                'Implementation-Version'  : project.jar.archiveVersion,
                'Implementation-Vendor'   : mod_authors,
                'Implementation-Timestamp': new Date().format("yyyy-MM-dd'T'HH:mm:ssZ")
        ])
    }
    
    finalizedBy 'reobfJar'
}

publishing {
    publications {
        register('mavenJava', MavenPublication) {
            artifact jar
        }
    }
    repositories {
        maven {
            url "file://${project.projectDir}/mcmodsrepo"
        }
    }
}

tasks.withType(JavaCompile).configureEach {
    options.encoding = 'UTF-8'
}

 

 

Were you able to figure this out? 
I have the same issue when trying to import a dependency as well (okhttp, imported from maven via `minecraftLibrary` in ForgeGradle)

Unfortunately not. In my case I was able to just copy my whole library code into my project, which is really bad practice, but seems to be the only option until the forge team develops a usable and working interface for non-mod libs...