CsvJdbc
a Java database driver for reading comma-separated-value files
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CsvJdbca Java database driver for reading comma-separated-value files |
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Driver Properties
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CsvJdbc is a read-only JDBC driver that uses Comma Separated Value (CSV) files or DBF files as database tables. It is ideal for writing data import programs or analyzing log files.
The driver enables you to access a directory or a ZIP file containing CSV or DBF files as if it were a database containing tables. As there is no real database management system behind the scenes, not all JDBC functionality is available.
The CsvJdbc driver is used just like any other JDBC driver:
The following example puts the above steps into practice.
import java.sql.*;
public class DemoDriver
{
public static void main(String[] args)
{
try
{
// Load the driver.
Class.forName("org.relique.jdbc.csv.CsvDriver");
// Create a connection. The first command line parameter is
// the directory containing the .csv files.
// A single connection is thread-safe for use by several threads.
Connection conn = DriverManager.getConnection("jdbc:relique:csv:" + args[0]);
// Create a Statement object to execute the query with.
// A Statement is not thread-safe.
Statement stmt = conn.createStatement();
// Select the ID and NAME columns from sample.csv
ResultSet results = stmt.executeQuery("SELECT ID,NAME FROM sample");
// Dump out the results
while (results.next())
{
System.out.println("ID= " + results.getString("ID") +
" NAME= " + results.getString("NAME"));
}
// Clean up
results.close();
stmt.close();
conn.close();
}
catch(Exception e)
{
e.printStackTrace();
}
}
}
Like other databases, creating a scrollable statement enables scrolling forwards and backwards through result sets. This is demonstrated in the following example.
package org.relique.jdbc.csv;
import java.sql.*;
public class DemoDriver2
{
public static void main(String[] args)
{
try
{
Class.forName("org.relique.jdbc.csv.CsvDriver");
Connection conn = DriverManager.getConnection("jdbc:relique:csv:" + args[0]);
// create a scrollable Statement so we can move forwards and backwards
// through ResultSets
Statement stmt = conn.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE,
ResultSet.CONCUR_READ_ONLY);
ResultSet results = stmt.executeQuery("SELECT ID,NAME FROM sample");
// dump out the last record in the result set, then the first record
if (results.last())
{
System.out.println("ID= " + results.getString("ID") +
" NAME= " + results.getString("NAME"));
if (results.first())
{
System.out.println("ID= " + results.getString("ID") +
" NAME= " + results.getString("NAME"));
}
}
// clean up
results.close();
stmt.close();
conn.close();
}
catch(Exception e)
{
e.printStackTrace();
}
}
}
To read several files (for example, daily log files) as a single table, set the database connection property indexedFiles. The following example demonstrates how to do this.
import java.sql.*;
import java.util.Properties;
public class DemoDriver3
{
public static void main(String[] args)
{
try
{
Class.forName("org.relique.jdbc.csv.CsvDriver");
Properties props = new Properties();
props.put("fileExtension", ".txt");
props.put("indexedFiles", "true");
// We want to read test-001-20081112.txt, test-002-20081113.txt and many
// other files matching this pattern.
props.put("fileTailPattern", "-(\\d+)-(\\d+)");
// Make the two groups in the regular expression available as
// additional table columns.
props.put("fileTailParts", "Seqnr,Logdatum");
Connection conn = DriverManager.getConnection("jdbc:relique:csv:" +
args[0], props);
Statement stmt = conn.createStatement();
ResultSet results = stmt.executeQuery("SELECT Datum, Station, " +
"Seqnr, Logdatum FROM test");
ResultSetMetaData meta = results.getMetaData();
while (results.next())
{
for (int i = 0; i < meta.getColumnCount(); i++)
{
System.out.println(meta.getColumnName(i + 1) + " " +
results.getString(i + 1));
}
}
results.close();
stmt.close();
conn.close();
}
catch(Exception e)
{
e.printStackTrace();
}
}
}
Set the database connection property columnTypes to enable expressions containing numeric, time and date data types to be used in SELECT statements and to enable column values to be fetched using ResultSet.getInt, getDouble, getTime and other ResultSet.get methods.
import java.sql.*;
import java.util.Properties;
public class DemoDriver4
{
public static void main(String[] args)
{
try
{
Class.forName("org.relique.jdbc.csv.CsvDriver");
Properties props = new Properties();
// Define column names and column data types here.
props.put("suppressHeaders", "true");
props.put("headerline", "ID,ANGLE,MEASUREDATE");
props.put("columnTypes", "Int,Double,Date");
Connection conn = DriverManager.getConnection("jdbc:relique:csv:" +
args[0], props);
Statement stmt = conn.createStatement();
ResultSet results = stmt.executeQuery("SELECT Id, Angle * 180 / 3.1415 as A, " +
"MeasureDate FROM t1 where Id > 1001");
while (results.next())
{
// Fetch column values with methods that match the column data types.
System.out.println(results.getInt(1));
System.out.println(results.getDouble(2));
System.out.println(results.getDate(3));
}
results.close();
stmt.close();
conn.close();
}
catch(Exception e)
{
e.printStackTrace();
}
}
}
To read the compressed files inside a ZIP file as database tables, make a database connection to the ZIP file using the JDBC connection string format jdbc:relique:csv:zip:filename.zip. This is demonstrated in the following example.
import java.sql.*;
import java.util.Properties;
public class DemoDriver5
{
public static void main(String[] args)
{
try
{
Class.forName("org.relique.jdbc.csv.CsvDriver");
String zipFilename = args[0];
Connection conn = DriverManager.getConnection("jdbc:relique:csv:zip:" +
zipFilename);
Statement stmt = conn.createStatement();
// Read from file mytable.csv inside the ZIP file
ResultSet results = stmt.executeQuery("SELECT * FROM mytable");
while (results.next())
{
System.out.println(results.getString("COUNTRY"));
}
results.close();
stmt.close();
conn.close();
}
catch(Exception e)
{
e.printStackTrace();
}
}
}
To read data that is either held inside the Java application (for example, in a JAR file) or accessed remotely (for example, using HTTP requests), create a Java class that implements the interface org.relique.io.TableReader and give this class name in the connection URL. CsvJdbc then creates an instance of this class and calls the getReader method to obtain a java.io.Reader for each database table being read. This is demonstrated in the following two Java classes.
import java.io.*;
import java.sql.*;
import java.util.*;
import org.relique.io.TableReader;
public class MyTableReader implements TableReader
{
public Reader getReader(Statement statement, String tableName) throws SQLException
{
if (tableName.equalsIgnoreCase("ELEMENT"))
return new StringReader("ATOMIC_NUMBER,SYMBOL,NAME\n" +
"1,H,Hydrogen\n2,He,Helium\n3,Li,Lithium\n");
throw new SQLException("Table does not exist: " + tableName);
}
public List getTableNames(Connection connection) throws SQLException
{
Vector v = new Vector();
v.add("ELEMENT");
return v;
}
}
import java.sql.*;
public class DemoDriver6
{
public static void main(String []args)
{
try
{
Class.forName("org.relique.jdbc.csv.CsvDriver");
// Give name of Java class that provides database tables.
Connection conn = DriverManager.getConnection("jdbc:relique:csv:class:" +
MyTableReader.class.getName());
Statement stmt = conn.createStatement();
String sql = "SELECT Atomic_Number from element where Symbol='Li'";
ResultSet results = stmt.executeQuery(sql);
results.next();
System.out.println(results.getString(1));
results.close();
stmt.close();
conn.close();
}
catch (Exception e)
{
e.printStackTrace();
}
}
}
CsvJdbc accepts all types of CSV files defined by RFC 4180.
CsvJdbc accepts only SQL SELECT queries from a single table and does not support INSERT, UPDATE, DELETE or CREATE statements. Joins between tables in SQL SELECT queries are not supported.
SQL SELECT queries must be of the following format.
SELECT [DISTINCT] [table-alias.]column [[AS] alias], ... FROM table [[AS] table-alias] WHERE [NOT] condition [AND | OR condition] ... GROUP BY column ... [HAVING condition ...] ORDER BY column [ASC | DESC] ... LIMIT n [OFFSET n]
Each column is either a named column, *, a constant value, NULL, CURRENT_DATE, or an expression including functions LENGTH, LOWER, ROUND, UPPER, aggregate functions AVG, COUNT, MAX, MIN, SUM and operations +, -, /, * and parentheses. Supported comparisons in the optional WHERE clause are <, >, <=, >=, =, !=, <>, NOT, BETWEEN, LIKE, IS NULL, IN.
For queries containing ORDER BY, all records are read into memory and sorted. For queries containing GROUP BY plus an aggregate function, all records are read into memory and grouped. For queries that produce a scrollable result set, all records up to the furthest accessed record are held into memory. For other queries, CsvJdbc holds only one record at a time in memory.
CsvJdbc requires Java version 1.6, or later. For reading DBF files, DANS DBF Library must be downloaded and included in the CLASSPATH.
The driver also supports a number of parameters that change the default behaviour of the driver.
These properties are:
This following example code shows how some of these properties are used.
...
Properties props = new java.util.Properties();
props.put("separator", "|"); // separator is a bar
props.put("suppressHeaders", "true"); // first line contains data
props.put("fileExtension", ".txt"); // file extension is .txt
props.put("timeZoneName", "America/Los_Angeles"); // timestamps are Los Angeles time
Connection conn1 = Drivermanager.getConnection("jdbc:relique:csv:" + args[0], props);
...
// Connections using a URL string containing both directory and
// properties are also accepted (class java.net.URLEncoder encodes
// URL strings containing special characters).
Connection conn2 = DriverManager.getConnection("jdbc:relique:csv:" + args[0] +
"?separator=" + URLEncoder.encode("|", "UTF-8") +
"&fileExtension=.txt&suppressHeaders=true");
To checkout and build the latest CsvJdbc source code, use the following commands (git and ant must first be installed).
git clone git://git.code.sf.net/p/csvjdbc/code csvjdbc-code cd csvjdbc-code cd build ant jar cd .. cd release dir csvjdbc.jar
To include CsvJdbc in a Maven project, add the following lines to the pom.xml file.
<project>
...
<repositories>
<repository>
<id>SourceForge</id>
<url>http://csvjdbc.sourceforge.net/maven2</url>
</repository>
</repositories>
<dependencies>
<dependency>
<groupId>net.sourceforge.csvjdbc</groupId>
<artifactId>csvjdbc</artifactId>
<version>1.0.13</version>
</dependency>
</dependencies>
CsvJdbc is released under the GNU Lesser General Public License (LGPL).
Last modified: 06 May 2013 by Simon Chenery (simoc)