Remove hard dependency on Slf4J in API

bsideup · bsideup · commit 3786292fabd9 · 2019-11-25T22:01:43.000+01:00
diff --git a/docker-java-api/pom.xml b/docker-java-api/pom.xml
@@ -26,6 +26,7 @@
 			<groupId>org.slf4j</groupId>
 			<artifactId>slf4j-api</artifactId>
 			<version>${slf4j-api.version}</version>
+			<scope>provided</scope>
 		</dependency>
 
 		<dependency>
diff --git a/docker-java-api/src/main/java/com/github/dockerjava/api/async/ResultCallbackTemplate.java b/docker-java-api/src/main/java/com/github/dockerjava/api/async/ResultCallbackTemplate.java
@@ -10,6 +10,7 @@
 import java.io.IOException;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.TimeUnit;
+import java.util.function.Consumer;
 
 /**
  * Abstract template implementation of {@link ResultCallback}
@@ -20,7 +21,19 @@
 public abstract class ResultCallbackTemplate<RC_T extends ResultCallback<A_RES_T>, A_RES_T> implements
         ResultCallback<A_RES_T> {
 
-    private static final Logger LOGGER = LoggerFactory.getLogger(ResultCallbackTemplate.class);
+    private static final Consumer<Throwable> ERROR_LOGGER;
+
+    static {
+        Consumer<Throwable> errorLogger = e -> {};
+        try {
+            if (Class.forName("org.slf4j.LoggerFactory") != null) {
+                Logger LOGGER = LoggerFactory.getLogger(ResultCallbackTemplate.class);
+                errorLogger = e -> LOGGER.error("Error during callback", e);
+            }
+        } catch (ClassNotFoundException ignored) {
+        }
+        ERROR_LOGGER = errorLogger;
+    }
 
     private final CountDownLatch started = new CountDownLatch(1);
 
@@ -49,7 +62,7 @@ public void onError(Throwable throwable) {
         }
 
         try {
-            LOGGER.error("Error during callback", throwable);
+            ERROR_LOGGER.accept(throwable);
         } finally {
             try {
                 close();
diff --git a/docker-java/src/test/java/com/github/dockerjava/api/async/ResultCallbackTemplateTest.java b/docker-java/src/test/java/com/github/dockerjava/api/async/ResultCallbackTemplateTest.java
@@ -0,0 +1,55 @@
+package com.github.dockerjava.api.async;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+import java.io.File;
+import java.net.MalformedURLException;
+import java.net.URL;
+import java.net.URLClassLoader;
+import java.util.Set;
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+public class ResultCallbackTemplateTest {
+
+    static Set<URL> CLASSPATH = Stream.of(System.getProperty("java.class.path").split(":"))
+            .map(it -> {
+                try {
+                    return new File(it).toURI().toURL();
+                } catch (MalformedURLException e) {
+                    throw new RuntimeException(e);
+                }
+            })
+            .collect(Collectors.toSet());
+
+    @Test
+    public void shouldNotFailIfSlf4jIsNotOnClasspath() throws Exception {
+        try(
+                URLClassLoader classLoader = new URLClassLoader(
+                        CLASSPATH.stream().filter(it -> !it.getPath().contains("slf4j")).toArray(URL[]::new),
+                        null
+                )
+        ) {
+            Class<?> clazz = classLoader.loadClass(DummyResultCallbackTemplate.class.getName());
+            Object template = clazz.newInstance();
+            AtomicBoolean classNotFound = new AtomicBoolean();
+            clazz.getMethod("onNext", AtomicBoolean.class).invoke(template, classNotFound);
+            Assert.assertTrue("Slf4J is not on classpath", classNotFound.get());
+            clazz.getMethod("onError", Throwable.class).invoke(template, new Exception("Boom"));
+        }
+    }
+
+    public static class DummyResultCallbackTemplate extends ResultCallbackTemplate<DummyResultCallbackTemplate, AtomicBoolean> {
+
+        @Override
+        public void onNext(AtomicBoolean atomicBoolean) {
+            try {
+                atomicBoolean.set(Class.forName("org.slf4j.LoggerFactory") == null);
+            } catch (ClassNotFoundException ignored) {
+                atomicBoolean.set(true);
+            }
+        }
+    }
+}
