Add example for accessing existing SPDX objects

examples/org/spdx/examples/ExistingSpdxDocument.java

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+/**
+ * SPDX-License-Identifier: Apache-2.0
+ * Copyright (c) 2021 Source Auditor Inc.
+ */
+package org.spdx.examples;
+
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.FileNotFoundException;
+import java.io.IOException;
+import java.io.InputStream;
+import java.util.Collection;
+import java.util.Optional;
+
+import org.spdx.jacksonstore.MultiFormatStore;
+import org.spdx.jacksonstore.MultiFormatStore.Format;
+import org.spdx.library.InvalidSPDXAnalysisException;
+import org.spdx.library.ModelCopyManager;
+import org.spdx.library.SpdxConstants;
+import org.spdx.library.model.ModelObject;
+import org.spdx.library.model.SpdxDocument;
+import org.spdx.library.model.SpdxElement;
+import org.spdx.library.model.SpdxModelFactory;
+import org.spdx.storage.ISerializableModelStore;
+import org.spdx.storage.simple.InMemSpdxStore;
+
+/**
+ * This example demonstrate opening an existing SPDX document and accessing it.  The format
+ * for this example is assumed to be JSON (e.g. the output of the SimpleSpdxDocument example).
+ * Different format can be used by using the associated store rather than the spdx-jackson store
+ * (e.g. spdx-spreadsheet-store, spdx-tagvalue-store, or the spdx-rdf-store).
+ * 
+ * This example depends on the Spdx-Java-Library and the spdx-java-jackson store libraries
+ * 
+ * @author Gary O'Neall
+ *
+ */
+public class ExistingSpdxDocument {
+
+	/**
+	 * @param args args[0] is the file path containing the SPDX document
+	 */
+	public static void main(String[] args) {
+		if (args.length != 1) {
+			usage();
+			System.exit(1);
+		}
+		File inputFile = new File(args[0]);
+		if (!inputFile.exists()) {
+			System.out.println("Input file does not exist: "+args[0]);
+			System.exit(1);
+		}
+
+		/*
+		 * First thing we need is a store deseralize the SPDX document into.
+		 * We'll chose the MultiFormatStore since it supports serializing to JSON files
+		 * It takes an underlying model store as the first parameter - the inMemSpdxStore is a simple
+		 * built in store included in the Spdx-Java-Library.  The second parameter is the format
+		 * to use when serializing or deserializing
+		 */
+		ISerializableModelStore modelStore = new MultiFormatStore(new InMemSpdxStore(), Format.JSON_PRETTY);
+		/*
+		 * There are several other choices which can be made for a model store - most of which 
+		 * are in separate libraries that need to be included as dependencies.  Below are a few examples:
+		 * IModelStore modelStore = new InMemSpdxStore(); - the simplest store, but does not support serializing or deserializing
+		 * ISerializableModelStore modelStore = new TagValueStore(new InMemSpdxStore()); Supports serializing and deserializing SPDX tag/value files
+		 * ISerializableModelStore modelStore = new RdfStore(); Supports serializing and deserializing various RDF formats (e.g. RDF/XML, RDF/Turtle)
+		 * ISerializableModelStore modelStore = new SpreadsheetStore(new InMemSpdxStore()); Supports serializing and deserializing .XLS or .XLSX spreadsheets
+		 */
+
+		/* 
+		 * The ModelCopyManager is used when using more than one Model Store.  The Listed Licenses uses
+		 * it's own model store, so we will need a ModelCopyManager to manage the copying of the listed
+		 * license information over to the document model store
+		 */
+		ModelCopyManager copyManager = new ModelCopyManager();
+		String documentUri = null;
+		// Let's deseralize the document
+		try (InputStream stream = new FileInputStream(inputFile)) {
+			documentUri = modelStore.deSerialize(stream, false);
+		} catch (FileNotFoundException e1) {
+			System.out.println("Input file does not exist: "+args[0]);
+			System.exit(1);
+		} catch (IOException e1) {
+			System.out.println("I/O error reading input file: "+args[0]);
+			System.exit(1);
+		} catch (InvalidSPDXAnalysisException e) {
+			System.out.println("The SPDX document is not valid: "+e.getMessage());
+			System.exit(1);
+		}
+		// Now that the document is deserialized, we can access it using the SpdxModelFactory
+		try {
+			// To access the existing document, simply create the SPDX document passing in the 
+			// model store and document URI as parameters
+			SpdxDocument document = new SpdxDocument(modelStore, documentUri, copyManager, false);
+			// Note that all class objects in the Spdx Java Library follow the same pattern - 
+			// to access any existing object in the store, simply create the object passing in 
+			// the document URI, model store and the ID for the object
+
+			// Another (more cumbersome) approach is to use the model factory
+			Optional<ModelObject> optionalDocument2 = SpdxModelFactory.getModelObject(modelStore, documentUri, SpdxConstants.SPDX_DOCUMENT_ID, copyManager);
+			if (!optionalDocument2.isPresent()) {
+				System.out.println("The SPDX document is not present in the model");
+				// Note - this should never happen
+				System.exit(1);
+			}
+			// When using the factory method, we have to type cast the result
+			SpdxDocument document2 = (SpdxDocument)optionalDocument2.get();
+			// Since the 2 documents are just references to the same object, they will always be equivalent
+			if (!document.equivalent(document2)) {
+				System.out.println("Oops - these 2 documents should be the same");
+				System.exit(1);
+			}
+			// Let's see find what the document is describing
+			Collection<SpdxElement> described = document.getDocumentDescribes();
+			for (SpdxElement des:described) {
+				System.out.println("The document described ID "+des.getId());
+			}
+			System.exit(0);
+		} catch (InvalidSPDXAnalysisException e) {
+			System.out.println("Unexpected error reading SPDX document: "+e.getMessage());
+			System.exit(1);
+		}
+	}
+
+	private static void usage() {
+		System.out.println("Usage: ExistingSpxDocument inputFilePath");
+	}
+
+}