Create a Data Access Object for HDFS Data using JDBI

JDBI is a SQL convenience library for Java that exposes two different style APIs, a fluent style and a SQL object style. The CData JDBC Driver for HDFS integrates connectivity to live HDFS data in Java applications. By pairing these technologies, you gain simple, programmatic access to HDFS data. This article explains how to build a basic Data Access Object (DAO) and the accompanying code to read HDFS data.

Create a DAO for the HDFS Files Entity

The interface below declares the desired behavior for the SQL object to create a single method for each SQL statement to be implemented.

public interface MyFilesDAO {
 //request specific data from HDFS (String type is used for simplicity)
 @SqlQuery("SELECT ChildrenNum FROM Files WHERE FileId = :fileId")
 String findChildrenNumByFileId(@Bind("fileId") String fileId);

 /*
 * close with no args is used to close the connection
 */
 void close();
}

Open a Connection to HDFS

Collect the necessary connection properties and construct the appropriate JDBC URL for connecting to HDFS.

In order to authenticate, set the following connection properties:

• Host: Set this value to the host of your HDFS installation.
• Port: Set this value to the port of your HDFS installation. Default port: 50070

Built-in Connection String Designer

For assistance in constructing the JDBC URL, use the connection string designer built into the HDFS JDBC Driver. Either double-click the JAR file or execute the jar file from the command-line.

java -jar cdata.jdbc.hdfs.jar

Fill in the connection properties and copy the connection string to the clipboard.

A connection string for HDFS will typically look like the following:

jdbc:hdfs:Host=sandbox-hdp.hortonworks.com;Port=50070;Path=/user/root;User=root;

Use the configured JDBC URL to obtain an instance of the DAO interface. The particular method shown below will open a handle bound to the instance, so the instance needs to be closed explicitly to release the handle and the bound JDBC connection.

DBI dbi = new DBI("jdbc:hdfs:Host=sandbox-hdp.hortonworks.com;Port=50070;Path=/user/root;User=root;");
MyFilesDAO dao = dbi.open(MyFilesDAO.class);

//do stuff with the DAO

dao.close();

Read HDFS Data

With the connection open to HDFS, simply call the previously defined method to retrieve data from the Files entity in HDFS.

//disply the result of our 'find' method
String childrenNum = dao.findChildrenNumByFileId("119116");
System.out.println(childrenNum);

Since the JDBI library is able to work with JDBC connections, you can easily produce a SQL Object API for HDFS by integrating with the CData JDBC Driver for HDFS. Download a free trial and work with live HDFS data in custom Java applications today.