GH-3086: Allow for empty beans

parquet-hadoop/src/main/java/org/apache/parquet/format/converter/ParquetMetadataConverter.java

@@ -1591,7 +1591,9 @@ public FileMetaDataAndRowGroupOffsetInfo visit(RangeMetadataFilter filter) throw
 
     ParquetMetadata parquetMetadata =
         fromParquetMetadata(fileMetaData, fileDecryptor, encryptedFooter, rowGroupToRowIndexOffsetMap);
-    if (LOG.isDebugEnabled()) LOG.debug(ParquetMetadata.toPrettyJSON(parquetMetadata));
+    if (LOG.isDebugEnabled()) {
+      LOG.debug(ParquetMetadata.toPrettyJSON(parquetMetadata));
+    }
     return parquetMetadata;
   }
 

parquet-hadoop/src/main/java/org/apache/parquet/hadoop/metadata/ParquetMetadata.java

@@ -20,18 +20,20 @@
 
 import com.fasterxml.jackson.databind.ObjectMapper;
 import com.fasterxml.jackson.databind.ObjectWriter;
+import com.fasterxml.jackson.databind.SerializationFeature;
 import java.io.IOException;
 import java.io.StringReader;
 import java.io.StringWriter;
 import java.util.List;
 
 /**
  * Metadata block stored in the footer of the file
- * contains file level (Codec, Schema, ...) and block level (location, columns, record count, ...) meta data
+ * contains file level (Codec, Schema, ...) and block level (location, columns, record count, ...) metadata
  */
 public class ParquetMetadata {
 
-  private static final ObjectMapper objectMapper = new ObjectMapper();
+  private static final ObjectMapper objectMapper =
+      new ObjectMapper().configure(SerializationFeature.FAIL_ON_EMPTY_BEANS, false);
 
   /**
    * @param parquetMetaData an instance of parquet metadata to convert

parquet-hadoop/src/test/java/org/apache/parquet/hadoop/metadata/TestParquetMetadata.java

@@ -0,0 +1,113 @@
+/*
+ * 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.parquet.hadoop.metadata;
+
+import static org.apache.parquet.schema.LogicalTypeAnnotation.TimeUnit.MICROS;
+import static org.apache.parquet.schema.LogicalTypeAnnotation.TimeUnit.MILLIS;
+import static org.apache.parquet.schema.LogicalTypeAnnotation.TimeUnit.NANOS;
+import static org.apache.parquet.schema.PrimitiveType.PrimitiveTypeName.BINARY;
+import static org.apache.parquet.schema.PrimitiveType.PrimitiveTypeName.FIXED_LEN_BYTE_ARRAY;
+import static org.apache.parquet.schema.PrimitiveType.PrimitiveTypeName.FLOAT;
+import static org.apache.parquet.schema.PrimitiveType.PrimitiveTypeName.INT32;
+import static org.apache.parquet.schema.PrimitiveType.PrimitiveTypeName.INT64;
+import static org.junit.Assert.assertEquals;
+
+import com.fasterxml.jackson.databind.JsonNode;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import java.io.IOException;
+import java.net.URI;
+import java.net.URISyntaxException;
+import java.util.Collections;
+import org.apache.parquet.schema.LogicalTypeAnnotation;
+import org.apache.parquet.schema.MessageType;
+import org.apache.parquet.schema.Types;
+import org.junit.Test;
+
+public class TestParquetMetadata {
+  private static final String EXPECTED_JSON = "/test-expected-parquet-metadata.json";
+
+  // Use an object mapper, since order of the keys might differ in JSON maps,
+  // and we don't want to sort them because of testing
+  private static final ObjectMapper mapper = new ObjectMapper();
+
+  private static JsonNode expectedJson() throws IOException, URISyntaxException {
+    URI path = TestParquetMetadata.class.getResource(EXPECTED_JSON).toURI();
+    return mapper.readTree(path.toURL());
+  }
+
+  @Test
+  public void testToPrettyJSON() throws IOException, URISyntaxException {
+    MessageType complexParquetSchema = Types.buildMessage()
+        .addField(Types.optional(INT32)
+            .as(LogicalTypeAnnotation.intType(8))
+            .named("a"))
+        .addField(Types.optionalGroup()
+            .addField(Types.optional(INT32)
+                .as(LogicalTypeAnnotation.intType(16))
+                .named("c"))
+            .addField(Types.optional(BINARY)
+                .as(LogicalTypeAnnotation.stringType())
+                .named("d"))
+            .named("b"))
+        .addField(Types.optionalList()
+            .setElementType(Types.optional(INT32)
+                .as(LogicalTypeAnnotation.dateType())
+                .named("element"))
+            .named("e"))
+        .addField(Types.optionalList()
+            .setElementType(Types.optional(INT32)
+                .as(LogicalTypeAnnotation.dateType())
+                .named("element"))
+            .named("f"))
+        .addField(Types.optional(FLOAT).named("g"))
+        .addField(Types.optional(INT64)
+            .as(LogicalTypeAnnotation.timestampType(true, MILLIS))
+            .named("h"))
+        .addField(Types.optional(INT64)
+            .as(LogicalTypeAnnotation.timestampType(true, NANOS))
+            .named("i"))
+        .addField(Types.optional(INT64)
+            .as(LogicalTypeAnnotation.timestampType(false, MILLIS))
+            .named("j"))
+        .addField(Types.optional(INT64)
+            .as(LogicalTypeAnnotation.timestampType(true, MICROS))
+            .named("k"))
+        .addField(Types.optional(INT64)
+            .as(LogicalTypeAnnotation.timestampType(false, MICROS))
+            .named("l"))
+        .addField(Types.optional(FIXED_LEN_BYTE_ARRAY)
+            .length(12)
+            .as(LogicalTypeAnnotation.intervalType())
+            .named("m"))
+        .addField(Types.optionalMap()
+            .key(Types.optional(INT32)
+                .as(LogicalTypeAnnotation.dateType())
+                .named("key"))
+            .value(Types.optional(BINARY)
+                .as(LogicalTypeAnnotation.stringType())
+                .named("value"))
+            .named("list"))
+        .named("root");
+
+    FileMetaData fmd = new FileMetaData(complexParquetSchema, Collections.emptyMap(), "ASF");
+    String prettyJSon = ParquetMetadata.toPrettyJSON(new ParquetMetadata(fmd, Collections.emptyList()));
+
+    assertEquals(mapper.readTree(prettyJSon), expectedJson());
+  }
+}