This example is based on the code in the LibraryCrud.java sample file.

For more information about storing the contents of a local library, see Content Library Storage.

Note: For a complete and up-to-date version of the sample code, see the vSphere Automation SDK Java samples at GitHub.
...

// Create a StorageBacking instance for storing the library content on a datastore. 

     StorageBacking libraryBacking = new StorageBacking();
     libraryBacking.setType(Type.DATASTORE);

/* 
 * Pass the value of the datastore ManagedObjectReference. 
 * See the vSphere Web Services SDK Programming Guide 
 * and the vSphere Web Services SDK samples. In addition, the  vSphere
			 Automation SDK for Java provides  
 * the VimUtil utility class in the vmware.samples.vim.helpers package. 
 * You can use the utility to retrieve the ManagedObjectReference
 * of the datastore entity.
 */
     libraryBacking.setDatastoreId("datastore-123");

// Create a LibraryModel that represents a local library backed on a datastore.

      LibraryModel libraryModel = new LibraryModel();
      libraryModel.setName("AcmeLibrary");
      libraryModel.setDescription("Local library backed by VC datastore");
      libraryModel.setType(LibraryType.LOCAL);
      libraryModel.setStorageBackings(Collections.singletonList(libraryBacking));