我是 Spark SQL 的新手。我按照 DataBricks 的在线指南进行操作:https://docs.databricks.com/spark/latest/data-sources/sql-databases.html
我可以成功连接到 MySQL 实例并从中读取数据。但我不断从 Spark SQL 中收到各种 NoTableFound 或 NoDatabaseFound 错误。这是我的整个测试类的样子:
import org.apache.spark.SparkConf;
import org.apache.spark.api.java.JavaSparkContext;
import org.apache.spark.sql.Dataset;
import org.apache.spark.sql.SQLContext;
import org.apache.spark.sql.SparkSession;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.Properties;
public class MySqlConnectionTest {
private static final String MYSQL_USERNAME = "";
private static final String MYSQL_PASSWORD = "";
private static final String MYSQL_HOSTNAME = "";
private static final String MYSQL_PORT = "";
private static final String MYSQL_DATABASE = "";
private static final String MYSQL_URL = "jdbc:mysql://" + MYSQL_HOSTNAME + ":" + MYSQL_PORT + "/" + MYSQL_DATABASE + "?user=" + MYSQL_USERNAME + "&password=" + MYSQL_PASSWORD;
public static void main(String[] args) {
Properties connectionProperties = new Properties();
connectionProperties.put("user", MYSQL_USERNAME);
connectionProperties.put("password", MYSQL_PASSWORD);
/* First verify we are getting a valid connection!
try {
testConnection();
} catch(Exception e) {
e.printStackTrace();
} */
/*
* NONE of the writeToSummary methods work! The readFromSummary methods work fine...
* */
// writeToSummary(connectionProperties);
// writeToSummaryV2(connectionProperties);
writeToSummaryV3(connectionProperties);
}
private static void testConnection() throws ClassNotFoundException, SQLException {
Class.forName("com.mysql.jdbc.Driver");
Connection connection = DriverManager.getConnection(MYSQL_URL, MYSQL_USERNAME, MYSQL_PASSWORD);
boolean result = connection.isClosed();
System.out.println("@@ is connection closed?? ==> " + result);
}
private static SparkSession getSparkSession(){
return SparkSession.builder().master("local[2]").appName("readUsageSummaryV2").getOrCreate();
}
private static SQLContext getSqlContext() {
SparkConf sparkConf = new SparkConf()
.setAppName("saveUsageSummary")
.setMaster("local[2]");
JavaSparkContext javaSparkContext = new JavaSparkContext(sparkConf);
return new SQLContext(javaSparkContext);
}
private static void readFromSummary(Properties connectionProperties) {
Dataset dataSet = getSqlContext().read().jdbc(MYSQL_URL, "summary", connectionProperties);
dataSet.printSchema();
dataSet.select("id","cycle_key", "product", "access_method", "billed", "received_date")
.limit(5)
.show();
}
private static void readFromSummaryV2(Properties connectionProperties) {
Dataset dataSet = getSparkSession().read().jdbc(MYSQL_URL, "summary", connectionProperties);
dataSet.select("id","cycle_key", "product", "access_method", "billed", "received_date")
.limit(5)
.show();
}
private static void writeToSummary(Properties connectionProperties) {
SQLContext sqlContext = getSqlContext();
sqlContext.tables("usages")
.write()
// .mode(SaveMode.Append)
.jdbc(MYSQL_URL, "summary", connectionProperties);
}
private static void writeToSummaryV2(Properties connectionProperties) {
SQLContext sqlContext = getSqlContext();
sqlContext.table("summary")
.write()
// .mode(SaveMode.Append)
.jdbc(MYSQL_URL, "summary", connectionProperties);
}
private static void writeToSummaryV3(Properties connectionProperties) {
SQLContext sqlContext = getSqlContext();
sqlContext.sql("SELECT * FROM summary LIMIT 5")
.write()
// .mode(SaveMode.Append)
.jdbc(MYSQL_URL, "summary", connectionProperties);
}
}
最佳答案
答案总是很简单...我以新的眼光重新阅读了文档,并了解到要使其工作,Dataset.write() 方法必须编写 Spark SQL 上下文中已存在的内容。因此,我可以让它针对通过从数据库读取而创建的数据集进行写入,如下所示:
private static void writeToSummaryV4(Properties connectionProperties) {
Dataset summary = getSparkSession().read().jdbc(MYSQL_URL, "summary", connectionProperties);
summary.select("comp_code","cycle_key", "product", "access_method", "billed", "received_date")
.limit(5)
.show();
summary.write().mode(SaveMode.Append).jdbc(MYSQL_URL, "summary", connectionProperties);
}
关于java - 使用 Apache Spark SQLContext 写入时出错,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/43727319/