check needed classpath for engines

Author: nidi3

graphviz-java/src/main/java/guru/nidi/graphviz/engine/AbstractJsGraphvizEngine.java

@@ -27,17 +27,24 @@
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 
+import static guru.nidi.graphviz.engine.IoUtils.isOnClasspath;
 import static guru.nidi.graphviz.engine.IoUtils.readStream;
 import static java.util.stream.Collectors.joining;
 
 public abstract class AbstractJsGraphvizEngine extends AbstractGraphvizEngine {
+    private static final String VIZ_BASE = "META-INF/resources/webjars/viz.js-for-graphviz-java/2.1.2/";
+    static boolean AVAILABLE = isOnClasspath(VIZ_BASE + "viz.js");
     private static final Pattern FONT_NAME_PATTERN = Pattern.compile("\"?fontname\"?\\s*=\\s*\"?(.*?)[\",;\\]]");
     private static final Map<Class<?>, ThreadLocal<JavascriptEngine>> ENGINES = new HashMap<>();
     private final Supplier<JavascriptEngine> engineSupplier;
     private final FontMeasurer fontMeasurer = new FontMeasurer();
 
     protected AbstractJsGraphvizEngine(boolean sync, Supplier<JavascriptEngine> engineSupplier) {
         super(sync);
+        if (!AVAILABLE) {
+            throw new MissingDependencyException("Javascript engines are not available.",
+                    "org.webjars.npm:viz.js-for-graphviz-java");
+        }
         this.engineSupplier = engineSupplier;
     }
 
@@ -119,9 +126,8 @@ protected Entry<String, Options> preprocessCode(String src, Options options) {
     }
 
     private String vizJsCode() {
-        final String path = "/META-INF/resources/webjars/viz.js-for-graphviz-java/2.1.2/";
-        try (final InputStream api = getClass().getResourceAsStream(path + "viz.js");
-             final InputStream engine = getClass().getResourceAsStream(path + "full.render.js")) {
+        try (final InputStream api = getClass().getResourceAsStream("/" + VIZ_BASE + "viz.js");
+             final InputStream engine = getClass().getResourceAsStream("/" + VIZ_BASE + "full.render.js")) {
             return readStream(api) + readStream(engine);
         } catch (IOException e) {
             throw new AssertionError("Could not load internal javascript resources, is the jar file corrupt?", e);

graphviz-java/src/main/java/guru/nidi/graphviz/engine/Graphviz.java

@@ -17,6 +17,8 @@
 
 import guru.nidi.graphviz.model.Graph;
 import guru.nidi.graphviz.model.MutableGraph;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 import javax.annotation.Nullable;
 import java.io.*;
@@ -32,8 +34,11 @@
 import static java.util.Arrays.asList;
 
 public final class Graphviz {
+    private static final Logger LOG = LoggerFactory.getLogger(Graphviz.class);
+
     private static final Pattern DPI_PATTERN = Pattern.compile("\"?dpi\"?\\s*=\\s*\"?([0-9.]+)\"?",
             Pattern.CASE_INSENSITIVE);
+    private static final List<GraphvizEngine> AVAILABLE_ENGINES = availableEngines();
 
     @Nullable
     private static volatile BlockingQueue<GraphvizEngine> engineQueue;
@@ -64,9 +69,27 @@ private Graphviz(@Nullable MutableGraph graph, String src, @Nullable Rasterizer
         this.filters = filters;
     }
 
+    private static List<GraphvizEngine> availableEngines() {
+        final List<GraphvizEngine> engines = new ArrayList<>();
+        if (GraphvizCmdLineEngine.AVAILABLE) {
+            engines.add(new GraphvizCmdLineEngine());
+        }
+        if (GraphvizV8Engine.AVAILABLE) {
+            engines.add(new GraphvizV8Engine());
+        }
+        engines.add(new GraphvizServerEngine());
+        if (GraphvizJdkEngine.AVAILABLE) {
+            engines.add(new GraphvizJdkEngine());
+        }
+        if (engines.size() == 1) {
+            LOG.warn("Only GraphvizServerEngine is available." +
+                    " If you want to use other engines, please put the needed dependencies on the classpath.");
+        }
+        return engines;
+    }
+
     public static void useDefaultEngines() {
-        useEngine(new GraphvizCmdLineEngine(), new GraphvizV8Engine(),
-                new GraphvizServerEngine(), new GraphvizJdkEngine());
+        useEngine(AVAILABLE_ENGINES);
     }
 
     public static void useEngine(GraphvizEngine first, GraphvizEngine... rest) {

graphviz-java/src/main/java/guru/nidi/graphviz/engine/GraphvizCmdLineEngine.java

@@ -27,6 +27,7 @@
 import java.util.Optional;
 import java.util.concurrent.TimeUnit;
 
+import static guru.nidi.graphviz.engine.IoUtils.isOnClasspath;
 import static java.util.Locale.ENGLISH;
 
 /**
@@ -36,6 +37,7 @@
  */
 public class GraphvizCmdLineEngine extends AbstractGraphvizEngine {
     private static final Logger LOG = LoggerFactory.getLogger(AbstractGraphvizEngine.class);
+    static boolean AVAILABLE = isOnClasspath("org.apache.commons.exec.CommandLine");
 
     private final String envPath;
     private final CommandRunner cmdRunner;
@@ -51,6 +53,10 @@ public GraphvizCmdLineEngine() {
 
     public GraphvizCmdLineEngine(String envPath, CommandLineExecutor executor) {
         super(true);
+        if (!AVAILABLE) {
+            throw new MissingDependencyException("Command line engine is not available.",
+                    "org.apache.commons:commons-exec");
+        }
         this.envPath = envPath;
         cmdRunner = new CommandBuilder()
                 .withShellWrapper(true)

graphviz-java/src/main/java/guru/nidi/graphviz/engine/GraphvizJdkEngine.java

@@ -15,22 +15,41 @@
  */
 package guru.nidi.graphviz.engine;
 
+import javax.annotation.Nullable;
+
+import static guru.nidi.graphviz.engine.IoUtils.isOnClasspath;
+
 public class GraphvizJdkEngine extends AbstractJsGraphvizEngine {
+    static boolean AVAILABLE = AbstractJsGraphvizEngine.AVAILABLE &&
+            (tryGraal() != null || isOnClasspath("net.arnx.nashorn.lib.PromiseException"));
+
     public GraphvizJdkEngine() {
         super(false, GraphvizJdkEngine::newEngine);
+        if (!AVAILABLE) {
+            throw new MissingDependencyException("JDK engine is not available", "net.arnx:nashorn-promise");
+        }
     }
 
     private static JavascriptEngine newEngine() {
+        final GraalJavascriptEngine graal = tryGraal();
+        return graal != null ? graal : new NashornJavascriptEngine();
+    }
+
+    @Nullable
+    private static GraalJavascriptEngine tryGraal() {
         try {
             return new GraalJavascriptEngine();
         } catch (ExceptionInInitializerError | NoClassDefFoundError | IllegalStateException e) {
-            return new NashornJavascriptEngine();
+            return null;
         }
     }
 
     @Override
     protected void doInit() {
-        engine().executeJavascript(promiseJsCode());
+        final JavascriptEngine engine = engine();
+        if (engine instanceof NashornJavascriptEngine) {
+            engine.executeJavascript(promiseJsCode());
+        }
         super.doInit();
     }
 }

graphviz-java/src/main/java/guru/nidi/graphviz/engine/GraphvizV8Engine.java

@@ -17,12 +17,19 @@
 
 import javax.annotation.Nullable;
 
+import static guru.nidi.graphviz.engine.IoUtils.isOnClasspath;
+
 public class GraphvizV8Engine extends AbstractJsGraphvizEngine {
+    static boolean AVAILABLE = AbstractJsGraphvizEngine.AVAILABLE && isOnClasspath("com.eclipsesource.v8.V8");
+
     public GraphvizV8Engine() {
         this(null);
     }
 
     public GraphvizV8Engine(@Nullable String extractionPath) {
         super(true, () -> new V8JavascriptEngine(extractionPath));
+        if (!AVAILABLE) {
+            throw new MissingDependencyException("V8 engine is not available.", "com.eclipsesource.j2v8:j2v8_*");
+        }
     }
 }

graphviz-java/src/main/java/guru/nidi/graphviz/engine/MissingDependencyException.java

@@ -0,0 +1,29 @@
+/*
+ * Copyright © 2015 Stefan Niederhauser ([email protected])
+ *
+ * Licensed 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 guru.nidi.graphviz.engine;
+
+public class MissingDependencyException extends GraphvizException {
+    private final String dependency;
+
+    public MissingDependencyException(String message, String dependency) {
+        super(message + " Missing '" + dependency + "' dependency.");
+        this.dependency = dependency;
+    }
+
+    public String getDependency() {
+        return dependency;
+    }
+}

graphviz-java/src/main/java/guru/nidi/graphviz/engine/Rasterizer.java

@@ -15,6 +15,8 @@
  */
 package guru.nidi.graphviz.engine;
 
+import org.slf4j.LoggerFactory;
+
 import javax.annotation.Nullable;
 import java.awt.*;
 import java.awt.image.BufferedImage;
@@ -28,7 +30,16 @@ public interface Rasterizer {
     @Nullable
     Rasterizer SALAMANDER = isOnClasspath("com.kitfox.svg.SVGDiagram") ? new SalamanderRasterizer() : null;
     @Nullable
-    Rasterizer DEFAULT = BATIK != null ? BATIK : SALAMANDER;
+    Rasterizer DEFAULT = getDefault();
+
+    @Nullable
+    static Rasterizer getDefault() {
+        final Rasterizer r = BATIK != null ? BATIK : SALAMANDER;
+        if (r == null) {
+            LoggerFactory.getLogger(Rasterizer.class).warn("Neither Batik nor Salamander found on classpath");
+        }
+        return r;
+    }
 
     static Rasterizer builtIn(String format) {
         return new BuiltInRasterizer(format, null, null);