Github user dkuppitz commented on a diff in the pull request:
https://github.com/apache/tinkerpop/pull/893#discussion_r205930559
--- Diff:
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/sideEffect/IoStep.java
---
@@ -0,0 +1,254 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.tinkerpop.gremlin.process.traversal.step.sideEffect;
+
+import org.apache.tinkerpop.gremlin.process.traversal.IO;
+import org.apache.tinkerpop.gremlin.process.traversal.Traversal;
+import org.apache.tinkerpop.gremlin.process.traversal.Traverser;
+import org.apache.tinkerpop.gremlin.process.traversal.step.ReadWriting;
+import
org.apache.tinkerpop.gremlin.process.traversal.step.util.AbstractStep;
+import org.apache.tinkerpop.gremlin.process.traversal.step.util.Parameters;
+import
org.apache.tinkerpop.gremlin.process.traversal.traverser.util.EmptyTraverser;
+import
org.apache.tinkerpop.gremlin.process.traversal.util.FastNoSuchElementException;
+import org.apache.tinkerpop.gremlin.structure.Graph;
+import org.apache.tinkerpop.gremlin.structure.io.GraphReader;
+import org.apache.tinkerpop.gremlin.structure.io.GraphWriter;
+import org.apache.tinkerpop.gremlin.structure.io.IoRegistry;
+import org.apache.tinkerpop.gremlin.structure.io.graphml.GraphMLReader;
+import org.apache.tinkerpop.gremlin.structure.io.graphml.GraphMLWriter;
+import org.apache.tinkerpop.gremlin.structure.io.graphson.GraphSONMapper;
+import org.apache.tinkerpop.gremlin.structure.io.graphson.GraphSONReader;
+import org.apache.tinkerpop.gremlin.structure.io.graphson.GraphSONWriter;
+import org.apache.tinkerpop.gremlin.structure.io.gryo.GryoMapper;
+import org.apache.tinkerpop.gremlin.structure.io.gryo.GryoReader;
+import org.apache.tinkerpop.gremlin.structure.io.gryo.GryoWriter;
+import org.apache.tinkerpop.gremlin.structure.util.StringFactory;
+
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+import java.lang.reflect.Method;
+import java.util.Collections;
+import java.util.List;
+import java.util.stream.Collectors;
+
+/**
+ * Handles read and write operations into the {@link Graph}.
+ *
+ * @author Stephen Mallette (http://stephen.genoprime.com)
+ */
+public class IoStep<S> extends AbstractStep<S,S> implements ReadWriting {
+
+ private Parameters parameters = new Parameters();
+ private boolean first = true;
+ private String file;
+ private Mode mode = Mode.UNSET;
+
+ public IoStep(final Traversal.Admin traversal, final String file) {
+ super(traversal);
+
+ if (null == file || file.isEmpty())
+ throw new IllegalArgumentException("file cannot be null or
empty");
+
+ this.file = file;
+ }
+
+ @Override
+ public void setMode(final Mode mode) {
+ this.mode = mode;
+ }
+
+ @Override
+ public Mode getMode() {
+ return mode;
+ }
+
+ @Override
+ public String getFile() {
+ return file;
+ }
+
+ @Override
+ public Parameters getParameters() {
+ return this.parameters;
+ }
+
+ @Override
+ public void configure(final Object... keyValues) {
+ this.parameters.set(null, keyValues);
+ }
+
+ @Override
+ protected Traverser.Admin<S> processNextStart() {
+ if (mode == Mode.UNSET) throw new IllegalStateException("IO mode
was not set to read() or write()");
+ if (!this.first) throw FastNoSuchElementException.instance();
+
+ this.first = false;
+ final File file = new File(this.file);
+
+ if (mode == Mode.READING) {
+ if (!file.exists()) throw new IllegalStateException(this.file
+ " does not exist");
+ return read(file);
+ } else if (mode == Mode.WRITING) {
+ return write(file);
+ } else {
+ throw new IllegalStateException("Invalid ReadWriting.Mode
configured in IoStep: " + mode.name());
+ }
+ }
+
+ private Traverser.Admin<S> write(final File file) {
+ try (final OutputStream stream = new FileOutputStream(file)) {
+ final Graph graph = (Graph) this.traversal.getGraph().get();
+ constructWriter().writeGraph(stream, graph);
+
+ return EmptyTraverser.instance();
+ } catch (IOException ioe) {
+ throw new IllegalStateException(String.format("Could not write
file %s from graph", this.file), ioe);
+ }
+ }
+
+ private Traverser.Admin<S> read(final File file) {
+ try (final InputStream stream = new FileInputStream(file)) {
--- End diff --
Just a comment here, unless you're gonna be like "oh, right, that's easy,
let me do that real quick...". It would be nice if this would not be hard-coded
to use `FileInputStream` and instead be flexible to use any file system (or
protocol). I know Java NIO has [some
methods](https://docs.oracle.com/javase/7/docs/api/java/nio/file/FileSystems.html)
to determine the file system from a URI, which can then be used to open an
`InputStream` / `OutputStream`. However, according to the docs it seems to
require a little bit more work (`FileSystemProvider` registration) and I have
no idea whether that's easy or not.
---
