Usage

Downloading and loading models from OmniHub — OmniHubUtils API

OmniHub exposes two entry points for loading pretrained models: the Pretrained facade (the recommended path for named models) and the lower-level OmniHubUtils class (useful when you have a filename and framework string and want direct control).

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The Pretrained Facade

org.eclipse.deeplearning4j.omnihub.models.Pretrained is the simplest way to load a known model. It provides static accessor methods for the two framework namespaces:

import org.eclipse.deeplearning4j.omnihub.models.Pretrained;

// Load the VGG19 (no-top) DL4J ComputationGraph
ComputationGraph vgg19 = Pretrained.dl4j().vgg19noTop(false);

// Load the AgeGoogLeNet SameDiff model
SameDiff ageGooglenet = Pretrained.samediff().ageGooglenet(false);

// Load ResNet18 SameDiff model
SameDiff resnet18 = Pretrained.samediff().resnet18(false);

The boolean argument is forceDownload. Pass true to delete the cached copy and re-download even if it already exists locally.

Pretrained.dl4j() returns a Dl4jModels instance. Pretrained.samediff() returns a SameDiffModels instance. Both classes are code-generated from the zoo manifest; their methods map directly to named model files.

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OmniHubUtils — Loading DL4J Models

Loading a MultiLayerNetwork

import org.eclipse.deeplearning4j.omnihub.OmniHubUtils;
import org.deeplearning4j.nn.multilayer.MultiLayerNetwork;

// Load from cache (download if not cached)
MultiLayerNetwork net = OmniHubUtils.loadNetwork("mymodel.zip");

// Force re-download even if cached
MultiLayerNetwork net = OmniHubUtils.loadNetwork("mymodel.zip", true);

loadNetwork downloads the file from the dl4j/ directory of the zoo, stores it in ~/.omnihub/dl4j/, and loads it using MultiLayerNetwork.load(file, true) (with the parameter updater restored).

Loading a ComputationGraph

import org.deeplearning4j.nn.graph.ComputationGraph;

ComputationGraph graph = OmniHubUtils.loadCompGraph("vgg19_weights_tf_dim_ordering_tf_kernels_notop.zip");

// With force download
ComputationGraph graph = OmniHubUtils.loadCompGraph(
    "vgg19_weights_tf_dim_ordering_tf_kernels_notop.zip",
    true
);

loadCompGraph is identical to loadNetwork except it calls ComputationGraph.load(file, true).

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OmniHubUtils — Loading SameDiff Models

import org.nd4j.autodiff.samediff.SameDiff;

SameDiff model = OmniHubUtils.loadSameDiffModel("age_googlenet.fb");

// With force download
SameDiff model = OmniHubUtils.loadSameDiffModel("age_googlenet.fb", true);

SameDiff models are stored as FlatBuffers files (.fb). They are downloaded from the samediff/ directory of the zoo and cached under ~/.omnihub/samediff/. Loading uses SameDiff.load(file, true).

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Direct Download with downloadAndLoadFromZoo

For cases where you want the local File handle rather than an already-loaded model object, call downloadAndLoadFromZoo directly:

import java.io.File;

File modelFile = OmniHubUtils.downloadAndLoadFromZoo(
    "samediff",           // framework subdirectory
    "resnet18.fb",        // filename
    false                 // forceDownload
);

// Now load it yourself
SameDiff sd = SameDiff.load(modelFile, true);

The framework string must match the subdirectory name in the zoo repository ("dl4j" or "samediff").

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Caching Behavior

Models are cached in the directory returned by OmnihubConfig.getOmnihubHome():

• Default: ~/.omnihub

• Custom: set the OMNIHUB_HOME environment variable before the JVM starts.

The cache structure is flat per-framework:

~/.omnihub/
  dl4j/
    vgg19_weights_tf_dim_ordering_tf_kernels_notop.zip
  samediff/
    age_googlenet.fb
    resnet18.fb

A download is skipped if the destination file already exists (unless forceDownload is true). There is no checksum verification in the current implementation — if you suspect a file is corrupt, pass forceDownload = true to replace it.

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Overriding the Zoo URL

By default, models are fetched from:

https://raw.githubusercontent.com/KonduitAI/omnihub-zoo/main

To point at a private mirror or a local HTTP server (for air-gapped environments), set the OMNIHUB_URL environment variable:

export OMNIHUB_URL=http://internal-mirror.example.com/omnihub

The URL is read by OmnihubConfig.getOmnihubUrl() each time a download is needed. The file is resolved at:

${OMNIHUB_URL}/${framework}/${name}

For example, OmniHubUtils.loadSameDiffModel("resnet18.fb") would fetch:

http://internal-mirror.example.com/omnihub/samediff/resnet18.fb

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Download Progress

OmniHubUtils wraps the download stream in a ProgressInputStream that prints a progress indicator to the console. The indicator is sized using an HTTP HEAD request to obtain the Content-Length before streaming begins. No configuration is needed; it activates automatically for every download.

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Full Example

import org.eclipse.deeplearning4j.omnihub.models.Pretrained;
import org.deeplearning4j.nn.graph.ComputationGraph;
import org.nd4j.linalg.factory.Nd4j;
import org.nd4j.linalg.api.ndarray.INDArray;

public class OmniHubExample {
    public static void main(String[] args) throws Exception {
        // Load VGG19 (no top layers) — downloads on first run, cached thereafter
        ComputationGraph vgg19 = Pretrained.dl4j().vgg19noTop(false);

        // VGG19 no-top expects input shape [batch, 3, 224, 224] (channels-first)
        INDArray input = Nd4j.rand(new int[]{1, 3, 224, 224});
        INDArray[] output = vgg19.output(input);

        System.out.println("VGG19 feature map shape: " + output[0].shapeInfoToString());
    }
}

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Next Steps

• Available Models — full catalog of models in the zoo, with input/output details.

• OmniHub Overview — architecture, configuration, and comparison with deeplearning4j-zoo.