Extract Assets from U3D via Java

//Source files that need to extract assets
String file = "template.u3d";

//create an instance of Scene
Scene scene = new Scene();
scene.open(file, FileFormat.UNIVERSAL3D);

//Create zip files and perform asset extraction on source files
String zipOutput ="OutputFile.zip";
File newFile=new File(zipOutput);
newFile.createNewFile();
FileOutputStream output = new FileOutputStream(zipOutput);
Zip za = new Zip(output);
Extract(scene,za,true);

//close stream resource
za.closeIo();

//Callable Extract method,The parameter texture indicates: whether to extract the texture
private void Extract(Scene scene, Zip za, boolean texture) throws IOException {
    Extractor extractor = new Extractor(za, texture);
    extractor.Extract(scene);
}

//Create a compressed file processing class
class Zip
{
    private ZipOutputStream archive;
    private HashSet<String> entries = new HashSet<String>();

    public Zip(OutputStream stream)
    {
        archive = new ZipOutputStream(stream);
    }

    public void Add(String fileName, byte[] content, boolean enableCompression) throws IOException {
        String entryName = PickName(fileName);
        if(enableCompression){
            archive.setLevel(5);
        }else{
            archive.setLevel(0);
        }
        ZipEntry entry = new ZipEntry(entryName);
        archive.putNextEntry(entry);
        archive.write(content, 0, content.length);
    }

    public void closeIo(){
        if(archive!=null){
            try {
                archive.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    private String PickName(String fileName)
    {
        if (!entries.contains(fileName))
        {
            entries.add(fileName);
            return fileName;
        }
        String arrFile[]=fileName.split(".");
        String baseName = arrFile[0];
        String ext = arrFile[1];
        for (int idx = 2; ; idx++)
        {
            String newName = baseName + "_" + idx;
            if (!StringUtils.isBlank(ext))
                newName += ext;
            if (entries.contains(newName))
                continue;
            entries.add(newName);
            return newName;
        }
    }
}

//Create an asset extraction processing class
class Extractor
{
    private Zip zip;
    private boolean texture;
    HashSet<A3DObject> visited = new HashSet<A3DObject>();

    public Extractor(Zip zip,boolean texture)
    {
        this.zip = zip;
        this.texture = texture;
    }

    private boolean CanVisit(A3DObject obj)
    {
        if (visited.contains(obj))
            return false;
        visited.add(obj);
        return true;
    }

    public void Extract(Scene scene) throws IOException {
        if (scene.getLibrary() != null && scene.getLibrary().size() > 0)
        {
            for (A3DObject obj:scene.getLibrary())
            {
                Visit(obj);
            }
        }
        VisitNode(scene.getRootNode());
    }

    private void VisitNode(Node node) throws IOException {
        if (!CanVisit(node))
            return;
        if (texture)
        {
            for (Material mat:node.getMaterials())
            {
                VisitMaterial(mat);
            }
        }

        for (Entity entity:node.getEntities())
        {
            if (entity instanceof Mesh){
                Save((Mesh)entity, node.getName());
            }
        }

        for (Node child:node.getChildNodes())
        {
            VisitNode(child);
        }
    }

    private void VisitMaterial(Material mat) throws IOException {
        if (!CanVisit(mat))
            return;
        if (!texture)
            return;
        for (TextureSlot tslot: mat)
        {
            if (tslot.getTexture() instanceof Texture)
            {
                Save((Texture)tslot.getTexture());
            }
        }
    }

    private void Visit(A3DObject obj) throws IOException {
        if (texture && obj instanceof Texture)
        {
            Save((Texture)obj);
        }
            else if (obj instanceof Mesh)
        {
            Save((Mesh)obj, null);
        }
            else if (obj instanceof Node)
        {
            VisitNode((Node)obj);
        }
    }

    private void Save(Mesh mesh, String nodeName) throws IOException {
        if (!CanVisit(mesh))
            return;
        Scene scene = new Scene(mesh);
        MemoryStream ms=new MemoryStream();
        scene.save(ms, FileFormat.FBX7400ASCII);
        String name = nodeName;
        if (StringUtils.isBlank(name))
            name = mesh.getName();
        if (StringUtils.isBlank(name))
            name = "mesh";
        String ext = ".fbx";
        zip.Add(name + ext, ms.toArray(), true);
    }

    private void Save(Texture tex) throws IOException {
        if (tex.getContent() == null || !CanVisit(tex))
            return;
        String fileName=tex.getFileName();
        if(tex.getFileName()!=null){
            String arrFile[]=fileName.split(".");
            fileName = arrFile[0];
        }
        zip.Add(fileName, tex.getContent(), false);
    }
}