GH-985: Correct unexpected behavior when using JavaLogger (#1047)

Fixes #985 

* JavaLogger(String name) added. Workaround for JavaLogger() provided
* JavaLogger() marked as deprecated. Workaround for JavaLogger() removed
* Little fix for note in README
* One more little fix for note in README
* JavaLogger(Class<?>) constructor added

README.md

@@ -738,13 +738,16 @@ public class Example {
   public static void main(String[] args) {
     GitHub github = Feign.builder()
                      .decoder(new GsonDecoder())
-                     .logger(new Logger.JavaLogger().appendToFile("logs/http.log"))
+                     .logger(new Logger.JavaLogger("GitHub.Logger").appendToFile("logs/http.log"))
                      .logLevel(Logger.Level.FULL)
                      .target(GitHub.class, "https://api.github.com");
   }
 }
 ```
 
+> **A Note on JavaLogger**: 
+> Avoid using of default ```JavaLogger()``` constructor - it was marked as deprecated and will be removed soon.
+
 The SLF4JLogger (see above) may also be of interest.
 
 

core/src/main/java/feign/Logger.java

@@ -16,6 +16,7 @@
 import java.io.IOException;
 import java.io.PrintWriter;
 import java.io.StringWriter;
+import java.util.concurrent.atomic.AtomicInteger;
 import java.util.logging.FileHandler;
 import java.util.logging.LogRecord;
 import java.util.logging.SimpleFormatter;
@@ -164,8 +165,44 @@ protected void log(String configKey, String format, Object... args) {
    */
   public static class JavaLogger extends Logger {
 
-    final java.util.logging.Logger logger =
-        java.util.logging.Logger.getLogger(Logger.class.getName());
+    final java.util.logging.Logger logger;
+
+    /**
+     * @deprecated Use {@link #JavaLogger(String)} or {@link #JavaLogger(Class)} instead.
+     *
+     *             This constructor can be used to create just one logger. Example =
+     *             {@code Logger.JavaLogger().appendToFile("logs/first.log")}
+     *
+     *             If you create multiple loggers for multiple clients and provide different files
+     *             to write log - you'll have unexpected behavior - all clients will write same log
+     *             to each file.
+     *
+     *             That's why this constructor will be removed in future.
+     */
+    @Deprecated
+    public JavaLogger() {
+      logger = java.util.logging.Logger.getLogger(Logger.class.getName());
+    }
+
+    /**
+     * Constructor for JavaLogger class
+     * 
+     * @param loggerName a name for the logger. This should be a dot-separated name and should
+     *        normally be based on the package name or class name of the subsystem, such as java.net
+     *        or javax.swing
+     */
+    public JavaLogger(String loggerName) {
+      logger = java.util.logging.Logger.getLogger(loggerName);
+    }
+
+    /**
+     * Constructor for JavaLogger class
+     *
+     * @param clazz the returned logger will be named after clazz
+     */
+    public JavaLogger(Class<?> clazz) {
+      logger = java.util.logging.Logger.getLogger(clazz.getName());
+    }
 
     @Override
     protected void logRequest(String configKey, Level logLevel, Request request) {

core/src/test/java/feign/MultipleLoggerTest.java

@@ -0,0 +1,55 @@
+/**
+ * Copyright 2012-2019 The Feign Authors
+ *
+ * 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 feign;
+
+import org.junit.Test;
+import java.lang.reflect.Field;
+
+public class MultipleLoggerTest {
+
+  private static java.util.logging.Logger getInnerLogger(Logger.JavaLogger logger)
+      throws Exception {
+    Field inner = logger.getClass().getDeclaredField("logger");
+    inner.setAccessible(true);
+    return (java.util.logging.Logger) inner.get(logger);
+  }
+
+  @Test
+  public void testAppendSeveralFilesToOneJavaLogger() throws Exception {
+    Logger.JavaLogger logger = new Logger.JavaLogger().appendToFile("1.log").appendToFile("2.log");
+    java.util.logging.Logger inner = getInnerLogger(logger);
+    assert (inner.getHandlers().length == 2);
+  }
+
+  @Test
+  public void testJavaLoggerInstantationWithLoggerName() throws Exception {
+    Logger.JavaLogger l1 = new Logger.JavaLogger("First client").appendToFile("1.log");
+    Logger.JavaLogger l2 = new Logger.JavaLogger("Second client").appendToFile("2.log");
+    java.util.logging.Logger logger1 = getInnerLogger(l1);
+    assert (logger1.getHandlers().length == 1);
+    java.util.logging.Logger logger2 = getInnerLogger(l2);
+    assert (logger2.getHandlers().length == 1);
+  }
+
+  @Test
+  public void testJavaLoggerInstantationWithClazz() throws Exception {
+    Logger.JavaLogger l1 = new Logger.JavaLogger(String.class).appendToFile("1.log");
+    Logger.JavaLogger l2 = new Logger.JavaLogger(Integer.class).appendToFile("2.log");
+    java.util.logging.Logger logger1 = getInnerLogger(l1);
+    assert (logger1.getHandlers().length == 1);
+    java.util.logging.Logger logger2 = getInnerLogger(l2);
+    assert (logger2.getHandlers().length == 1);
+  }
+
+}