[SPARK-11274] [SQL] Text data source support for Spark SQL.

This adds API for reading and writing text files, similar to SparkContext.textFile and RDD.saveAsTextFile.
```
SQLContext.read.text("/path/to/something.txt")
DataFrame.write.text("/path/to/write.txt")
```

Using the new Dataset API, this also supports
```
val ds: Dataset[String] = SQLContext.read.text("/path/to/something.txt").as[String]
```

Author: Reynold Xin <rxin@databricks.com>

Closes #9240 from rxin/SPARK-11274.

sql/core/src/main/resources/META-INF/services/org.apache.spark.sql.sources.DataSourceRegister

 org.apache.spark.sql.execution.datasources.jdbc.DefaultSource
 org.apache.spark.sql.execution.datasources.json.DefaultSource
 org.apache.spark.sql.execution.datasources.parquet.DefaultSource
+org.apache.spark.sql.execution.datasources.text.DefaultSource

sql/core/src/main/scala/org/apache/spark/sql/DataFrameReader.scala

@@ -302,6 +302,22 @@ class DataFrameReader private[sql](sqlContext: SQLContext) extends Logging {
     DataFrame(sqlContext, sqlContext.catalog.lookupRelation(TableIdentifier(tableName)))
   }
 
+  /**
+   * Loads a text file and returns a [[DataFrame]] with a single string column named "text".
+   * Each line in the text file is a new row in the resulting DataFrame. For example:
+   * {{{
+   *   // Scala:
+   *   sqlContext.read.text("/path/to/spark/README.md")
+   *
+   *   // Java:
+   *   sqlContext.read().text("/path/to/spark/README.md")
+   * }}}
+   *
+   * @param path input path
+   * @since 1.6.0
+   */
+  def text(path: String): DataFrame = format("text").load(path)
+
   ///////////////////////////////////////////////////////////////////////////////////////
   // Builder pattern config options
   ///////////////////////////////////////////////////////////////////////////////////////

sql/core/src/main/scala/org/apache/spark/sql/DataFrameWriter.scala

@@ -244,6 +244,8 @@ final class DataFrameWriter private[sql](df: DataFrame) {
    * @param connectionProperties JDBC database connection arguments, a list of arbitrary string
    *                             tag/value. Normally at least a "user" and "password" property
    *                             should be included.
+   *
+   * @since 1.4.0
    */
   def jdbc(url: String, table: String, connectionProperties: Properties): Unit = {
     val props = new Properties()
@@ -317,6 +319,22 @@ final class DataFrameWriter private[sql](df: DataFrame) {
    */
   def orc(path: String): Unit = format("orc").save(path)
 
+  /**
+   * Saves the content of the [[DataFrame]] in a text file at the specified path.
+   * The DataFrame must have only one column that is of string type.
+   * Each row becomes a new line in the output file. For example:
+   * {{{
+   *   // Scala:
+   *   df.write.text("/path/to/output")
+   *
+   *   // Java:
+   *   df.write().text("/path/to/output")
+   * }}}
+   *
+   * @since 1.6.0
+   */
+  def text(path: String): Unit = format("text").save(path)
+
   ///////////////////////////////////////////////////////////////////////////////////////
   // Builder pattern config options
   ///////////////////////////////////////////////////////////////////////////////////////

sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/json/JSONRelation.scala

@@ -161,11 +161,10 @@ private[json] class JsonOutputWriter(
     context: TaskAttemptContext)
   extends OutputWriter with SparkHadoopMapRedUtil with Logging {
 
-  val writer = new CharArrayWriter()
+  private[this] val writer = new CharArrayWriter()
   // create the Generator without separator inserted between 2 records
-  val gen = new JsonFactory().createGenerator(writer).setRootValueSeparator(null)
-
-  val result = new Text()
+  private[this] val gen = new JsonFactory().createGenerator(writer).setRootValueSeparator(null)
+  private[this] val result = new Text()
 
   private val recordWriter: RecordWriter[NullWritable, Text] = {
     new TextOutputFormat[NullWritable, Text]() {

sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/text/DefaultSource.scala

+/*
+ * 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.spark.sql.execution.datasources.text
+
+import com.google.common.base.Objects
+import org.apache.hadoop.fs.{Path, FileStatus}
+import org.apache.hadoop.io.{NullWritable, Text, LongWritable}
+import org.apache.hadoop.mapred.{TextInputFormat, JobConf}
+import org.apache.hadoop.mapreduce.lib.output.TextOutputFormat
+import org.apache.hadoop.mapreduce.{RecordWriter, TaskAttemptContext, Job}
+import org.apache.hadoop.mapreduce.lib.input.FileInputFormat
+
+import org.apache.spark.deploy.SparkHadoopUtil
+import org.apache.spark.mapred.SparkHadoopMapRedUtil
+import org.apache.spark.rdd.RDD
+import org.apache.spark.sql.catalyst.InternalRow
+import org.apache.spark.sql.catalyst.expressions.GenericMutableRow
+import org.apache.spark.sql.{AnalysisException, Row, SQLContext}
+import org.apache.spark.sql.execution.datasources.PartitionSpec
+import org.apache.spark.sql.sources._
+import org.apache.spark.sql.types.{StringType, StructType}
+import org.apache.spark.unsafe.types.UTF8String
+
+/**
+ * A data source for reading text files.
+ */
+class DefaultSource extends HadoopFsRelationProvider with DataSourceRegister {
+
+  override def createRelation(
+      sqlContext: SQLContext,
+      paths: Array[String],
+      dataSchema: Option[StructType],
+      partitionColumns: Option[StructType],
+      parameters: Map[String, String]): HadoopFsRelation = {
+    dataSchema.foreach(verifySchema)
+    new TextRelation(None, partitionColumns, paths)(sqlContext)
+  }
+
+  override def shortName(): String = "text"
+
+  private def verifySchema(schema: StructType): Unit = {
+    if (schema.size != 1) {
+      throw new AnalysisException(
+        s"Text data source supports only a single column, and you have ${schema.size} columns.")
+    }
+    val tpe = schema(0).dataType
+    if (tpe != StringType) {
+      throw new AnalysisException(
+        s"Text data source supports only a string column, but you have ${tpe.simpleString}.")
+    }
+  }
+}
+
+private[sql] class TextRelation(
+    val maybePartitionSpec: Option[PartitionSpec],
+    override val userDefinedPartitionColumns: Option[StructType],
+    override val paths: Array[String] = Array.empty[String])
+    (@transient val sqlContext: SQLContext)
+  extends HadoopFsRelation(maybePartitionSpec) {
+
+  /** Data schema is always a single column, named "text". */
+  override def dataSchema: StructType = new StructType().add("text", StringType)
+
+  /** This is an internal data source that outputs internal row format. */
+  override val needConversion: Boolean = false
+
+  /** Read path. */
+  override def buildScan(inputPaths: Array[FileStatus]): RDD[Row] = {
+    val job = new Job(sqlContext.sparkContext.hadoopConfiguration)
+    val conf = SparkHadoopUtil.get.getConfigurationFromJobContext(job)
+    val paths = inputPaths.map(_.getPath).sortBy(_.toUri)
+
+    if (paths.nonEmpty) {
+      FileInputFormat.setInputPaths(job, paths: _*)
+    }
+
+    sqlContext.sparkContext.hadoopRDD(
+      conf.asInstanceOf[JobConf], classOf[TextInputFormat], classOf[LongWritable], classOf[Text])
+      .mapPartitions { iter =>
+        var buffer = new Array[Byte](1024)
+        val row = new GenericMutableRow(1)
+        iter.map { case (_, line) =>
+          if (line.getLength > buffer.length) {
+            buffer = new Array[Byte](line.getLength)
+          }
+          System.arraycopy(line.getBytes, 0, buffer, 0, line.getLength)
+          row.update(0, UTF8String.fromBytes(buffer, 0, line.getLength))
+          row
+        }
+      }.asInstanceOf[RDD[Row]]
+  }
+
+  /** Write path. */
+  override def prepareJobForWrite(job: Job): OutputWriterFactory = {
+    new OutputWriterFactory {
+      override def newInstance(
+          path: String,
+          dataSchema: StructType,
+          context: TaskAttemptContext): OutputWriter = {
+        new TextOutputWriter(path, dataSchema, context)
+      }
+    }
+  }
+
+  override def equals(other: Any): Boolean = other match {
+    case that: TextRelation =>
+      paths.toSet == that.paths.toSet && partitionColumns == that.partitionColumns
+    case _ => false
+  }
+
+  override def hashCode(): Int = {
+    Objects.hashCode(paths.toSet, partitionColumns)
+  }
+}
+
+class TextOutputWriter(path: String, dataSchema: StructType, context: TaskAttemptContext)
+  extends OutputWriter
+  with SparkHadoopMapRedUtil {
+
+  private[this] val buffer = new Text()
+
+  private val recordWriter: RecordWriter[NullWritable, Text] = {
+    new TextOutputFormat[NullWritable, Text]() {
+      override def getDefaultWorkFile(context: TaskAttemptContext, extension: String): Path = {
+        val configuration = SparkHadoopUtil.get.getConfigurationFromJobContext(context)
+        val uniqueWriteJobId = configuration.get("spark.sql.sources.writeJobUUID")
+        val taskAttemptId = SparkHadoopUtil.get.getTaskAttemptIDFromTaskAttemptContext(context)
+        val split = taskAttemptId.getTaskID.getId
+        new Path(path, f"part-r-$split%05d-$uniqueWriteJobId$extension")
+      }
+    }.getRecordWriter(context)
+  }
+
+  override def write(row: Row): Unit = throw new UnsupportedOperationException("call writeInternal")
+
+  override protected[sql] def writeInternal(row: InternalRow): Unit = {
+    val utf8string = row.getUTF8String(0)
+    buffer.set(utf8string.getBytes)
+    recordWriter.write(NullWritable.get(), buffer)
+  }
+
+  override def close(): Unit = {
+    recordWriter.close(context)
+  }
+}

sql/core/src/test/resources/text-suite.txt

+This is a test file for the text data source
+1+1
+数据砖头
+"doh"

sql/core/src/test/scala/org/apache/spark/sql/execution/datasources/text/TextSuite.scala

+/*
+ * 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.spark.sql.execution.datasources.text
+
+import org.apache.spark.sql.test.SharedSQLContext
+import org.apache.spark.sql.types.{StringType, StructType}
+import org.apache.spark.sql.{AnalysisException, DataFrame, QueryTest, Row}
+import org.apache.spark.util.Utils
+
+
+class TextSuite extends QueryTest with SharedSQLContext {
+
+  test("reading text file") {
+    verifyFrame(sqlContext.read.format("text").load(testFile))
+  }
+
+  test("SQLContext.read.text() API") {
+    verifyFrame(sqlContext.read.text(testFile))
+  }
+
+  test("writing") {
+    val df = sqlContext.read.text(testFile)
+
+    val tempFile = Utils.createTempDir()
+    tempFile.delete()
+    df.write.text(tempFile.getCanonicalPath)
+    verifyFrame(sqlContext.read.text(tempFile.getCanonicalPath))
+
+    Utils.deleteRecursively(tempFile)
+  }
+
+  test("error handling for invalid schema") {
+    val tempFile = Utils.createTempDir()
+    tempFile.delete()
+
+    val df = sqlContext.range(2)
+    intercept[AnalysisException] {
+      df.write.text(tempFile.getCanonicalPath)
+    }
+
+    intercept[AnalysisException] {
+      sqlContext.range(2).select(df("id"), df("id") + 1).write.text(tempFile.getCanonicalPath)
+    }
+  }
+
+  private def testFile: String = {
+    Thread.currentThread().getContextClassLoader.getResource("text-suite.txt").toString
+  }
+
+  /** Verifies data and schema. */
+  private def verifyFrame(df: DataFrame): Unit = {
+    // schema
+    assert(df.schema == new StructType().add("text", StringType))
+
+    // verify content
+    val data = df.collect()
+    assert(data(0) == Row("This is a test file for the text data source"))
+    assert(data(1) == Row("1+1"))
+    // non ascii characters are not allowed in the code, so we disable the scalastyle here.
+    // scalastyle:off
+    assert(data(2) == Row("数据砖头"))
+    // scalastyle:on
+    assert(data(3) == Row("\"doh\""))
+    assert(data.length == 4)
+  }
+}