Java Example Code

Scenario

This section provides Java example code that demonstrates how to use a Spark job to access data from the GaussDB(DWS) data source.

A datasource connection has been created and bound to a queue on the DLI management console.

Hard coding passwords or storing them in code in plaintext poses significant security risks. You are advised to store them in encrypted form in configuration files or environment variables and decrypt them when needed to ensure security.

Preparations

1. Import dependencies.
   • Maven dependency involved

     1 2 3 4 5

     <dependency> <groupId>org.apache.spark</groupId> <artifactId>spark-sql_2.11</artifactId> <version>2.3.2</version> </dependency>

   • Import dependency packages.

     1	import org.apache.spark.sql.SparkSession;

2. Create a session.

   1	SparkSession sparkSession = SparkSession.builder().appName("datasource-dws").getOrCreate();

Accessing a Data Source Through a SQL API

1. Create a table to connect to a GaussDB(DWS) data source and set connection parameters.

   1	sparkSession.sql("CREATE TABLE IF NOT EXISTS dli_to_dws USING JDBC OPTIONS ('url'='jdbc:postgresql://10.0.0.233:8000/postgres','dbtable'='test','user'='dbadmin','password'='**')");

2. Insert data.

   1	sparkSession.sql("insert into dli_to_dws values(3,'Liu'),(4,'Xie')");

3. Query data.

   1	sparkSession.sql("select * from dli_to_dws").show();

   Response:

   

Submitting a Spark Job

1. Generate a JAR file based on the code file and upload the JAR file to the OBS bucket.
2. In the Spark job editor, select the corresponding dependency module and execute the Spark job.
   

   • For Spark 2.3.2 (soon to be taken offline) or 2.4.5, set Module to sys.datasource.dws when submitting a job.
   • If the Spark version is 3.1.1 or later, you do not need to select a module. Configure Spark parameters (--conf).

     spark.driver.extraClassPath=/usr/share/extension/dli/spark-jar/datasource/dws/*

     spark.executor.extraClassPath=/usr/share/extension/dli/spark-jar/datasource/dws/*

   • For how to submit a job on the console, see Table 3 "Parameters for selecting dependency resources" in Creating a Spark Job.
   • For details about how to submit a job through an API, see the description of the modules parameter in Table 2 "Request parameters" in Creating a Batch Processing Job.

Complete Example Code

Accessing GaussDB(DWS) tables through SQL APIs

import org.apache.spark.sql.SparkSession;
 
public class java_dws {
    public static void main(String[] args) {
        SparkSession sparkSession = SparkSession.builder().appName("datasource-dws").getOrCreate();
 
        sparkSession.sql("CREATE TABLE IF NOT EXISTS dli_to_dws USING JDBC OPTIONS ('url'='jdbc:postgresql://10.0.0.233:8000/postgres','dbtable'='test','user'='dbadmin','password'='**')");
 
        //*****************************SQL model***********************************
        //Insert data into the DLI data table
        sparkSession.sql("insert into dli_to_dws values(3,'Liu'),(4,'Xie')");
 
        //Read data from DLI data table
        sparkSession.sql("select * from dli_to_dws").show();
 
        //drop table
        sparkSession.sql("drop table dli_to_dws");
 
        sparkSession.close();
    }
}