HBASE-20804 Document and add tests for HBaseConfTool (#5190)

Signed-off-by: Duo Zhang <zhangduo@apache.org>

hbase-server/src/test/java/org/apache/hadoop/hbase/util/TestHBaseConfTool.java

@@ -0,0 +1,80 @@
+/*
+ * 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.hadoop.hbase.util;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotNull;
+
+import java.io.PrintStream;
+import java.util.LinkedList;
+import java.util.List;
+import org.apache.hadoop.hbase.HBaseClassTestRule;
+import org.apache.hadoop.hbase.master.cleaner.TimeToLiveLogCleaner;
+import org.apache.hadoop.hbase.testclassification.MiscTests;
+import org.apache.hadoop.hbase.testclassification.SmallTests;
+import org.junit.ClassRule;
+import org.junit.Test;
+import org.junit.experimental.categories.Category;
+
+@Category({ MiscTests.class, SmallTests.class })
+public class TestHBaseConfTool {
+
+  @ClassRule
+  public static final HBaseClassTestRule CLASS_RULE =
+    HBaseClassTestRule.forClass(TestHBaseConfTool.class);
+
+  @Test
+  public void testHBaseConfTool() {
+    String[] args = { TimeToLiveLogCleaner.TTL_CONF_KEY };
+    PrintStream stdout = System.out;
+
+    try {
+      DummyPrintStream printStream = new DummyPrintStream(System.out);
+      System.setOut(printStream);
+
+      HBaseConfTool.main(args);
+
+      List<String> printedLines = printStream.getPrintedLines();
+      assertNotNull(printedLines);
+      assertEquals(1, printedLines.size());
+      assertEquals(String.valueOf(TimeToLiveLogCleaner.DEFAULT_TTL), printedLines.get(0));
+    } finally {
+      // reset to standard output
+      System.setOut(stdout);
+    }
+  }
+
+  static class DummyPrintStream extends PrintStream {
+
+    private List<String> printedLines = new LinkedList<>();
+
+    public DummyPrintStream(PrintStream printStream) {
+      super(printStream);
+    }
+
+    @Override
+    public void println(String line) {
+      printedLines.add(line);
+      super.println(line);
+    }
+
+    public List<String> getPrintedLines() {
+      return printedLines;
+    }
+  }
+}

src/main/asciidoc/_chapters/ops_mgt.adoc

@@ -1296,6 +1296,15 @@ Options:
 
 ----
 
+[[ops.conf-tool]]
+=== HBase Conf Tool
+HBase Conf tool can be used to print out the current value of a configuration. It can be used by passing the configuration key on the command-line.
+
+[source, bash]
+----
+$ bin/hbase org.apache.hadoop.hbase.util.HBaseConfTool <configuration_key>
+----
+
 [[ops.regionmgt]]
 == Region Management