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CsvJdbc

a Java database driver for reading comma-separated-value files

About


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.

Usage


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 to a CSV file with the same format
      // using CsvJdbc helper function
      boolean append = true;
      CsvDriver.writeToCsv(results, System.out, append);

      // 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();
    }
  }
}

Features


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, CURRENT_TIME, or an expression including functions DAYOFMONTH, HOUROFDAY, LENGTH, LOWER, MINUTE, MONTH, NULLIF, ROUND, SECOND, TRIM, UPPER, YEAR, 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. Use double quotes around table names or column names contaning spaces or other special characters.

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.

Dependencies


CsvJdbc requires Java version 1.6, or later. For reading DBF files, DANS DBF Library must be downloaded and included in the CLASSPATH.

Driver Properties


The driver also supports a number of parameters that change the default behaviour of the driver.

These properties are:

charset
type: String
default: Java default
Defines the character set name of the files being read, such as UTF-16. See the Java Charset documentation for a list of available character set names.
columnTypes
type: String
default: all Strings
A comma-separated list defining SQL data types for columns in tables. When column values are fetched using getObject (as opposed to getString), the driver will parse the value and return a correctly typed object. If fewer data types are provided than the number of columns in the table, the last data type is repeated for all remaining columns. If columnTypes is set to an empty string then column types are inferred from the data. When working with multiple tables with different column types, define properties named columnTypes.CATS and columnTypes.DOGS to define different column types for tables CATS and DOGS.
commentChar
type: Character
default:
Lines before the header starting with this character are ignored. After the header has been read, all lines are interpreted as data.
cryptoFilterClassName
type: Class
default: null
The full class name of a Java class that decrypts the file being read. The class must implement interface org.relique.io.CryptoFilter. The class org.relique.io.XORFilter included in CsvJdbc implements an XOR encryption filter.
cryptoFilterParameterTypes
type: String
default: String
Comma-separated list of data types to pass to the constructor of the decryption class set in property cryptoFilterClassName.
cryptoFilterParameters
type: String
default:
Comma-separated list of values to pass to the constructor of the decryption class set in property cryptoFilterClassName.
defectiveHeaders
type: Boolean
default: False
in case a column name is the emtpy string, replace it with COLUMNx, where x is the ordinal identifying the column.
fileExtension
type: string
default: ".csv"
Specifies file extension of the CSV files. If the extension .dbf is used then files are read as dBase format database files.
fileTailParts
type: String
default: null
Comma-separated list of column names for the additional columns generated by regular expression groups in the property fileTailPattern.
fileTailPattern
type: String
default: null
Regular expression for matching filenames when property indexedFiles is True. If the regular expression contains groups (surrounded by parentheses) then the value of each group in matching filenames is added as an extra column to each line read from that file. For example, when querying table test, the regular expression -(\d+)-(\d+) will match files test-001-20081112.csv and test-002-20081113.csv. The column values 001 and 20081112 are added to each line read from the first file and 002 and 20081113 are added to each line read from the second file.
fileTailPrepend
type: Boolean
default: False
when True, columns generated by regular expression groups in the fileTailPattern property are prepended to the start of each line. When False, the generated columns are appended after the columns read for each line.
fixedWidths
type: String
default: null
Defines character position ranges for each column in a fixed width file. When set, column values are extracted from these ranges in each line instead of separating the line by delimiters. Each column is a pair of character positions separated by a minus sign, or a single character for columns with only a single character. The position of the first character on each line is 1. Character position ranges are separated by commas. For example, 1,2-9,16-19.
headerline
type: string
default: None
Used in combination with the suppressHeaders property to specify a custom header line for tables. headerline contains a list of column names for tables separated by the separator character. When working with multiple tables with different headers, define properties named headerline.CATS and headerline.DOGS to define different header lines for tables CATS and DOGS.
ignoreNonParseableLines
type: Boolean
default: False
when True, lines that cannot be parsed will not cause an exception but will be ignored. Each ignored line is logged. Call method java.sql.DriverManager.setLogWriter before executing a query to capture a list of ignored lines.
indexedFiles
type: Boolean
default: False
when True, all files with a filename matching the table name plus the regular expression given in property fileTailPattern are read as if they were a single file.
isHeaderFixedWidth
type: Boolean
default: True
Used in combination with the fixedWidths property when reading fixed width files to specify whether the header line containing the column names is also fixed width. If False, column names are separated by the separator character.
quotechar
type: Character
default: "
Defines quote character. Column values surrounded with the quote character are parsed with the quote characters removed. This is useful when values contain the separator character or line breaks. Only one character is allowed.
quoteStyle
type: String
default: SQL
Defines how a quote character is interpreted inside a quoted value. When SQL, a pair of quote characters together is interpreted as a single quote character. When C, a backslash followed by a quote character is interpreted as a single quote character.
locale
type: String
default: Java default
Defines locale to use when parsing timestamps. This is important when parsing words such as December which vary depending on the locale. Call method Locale.toString() to convert a locale to a string.
separator
type: character
default: ','
Used to specify a different column separator.
skipLeadingLines
type: Integer
default: 0
after opening a file, skip this many lines before starting to interpret the contents.
skipLeadingDataLines
type: Integer
default: 0
after reading the header from a file, skip this many lines before starting to interpret lines as records.
suppressHeaders
type: boolean
default: False
Used to specify that the file does not contain a column header with column names. If True and headerline is not set, then columns are named sequentially COLUMN1, COLUMN2, ... If False, the column header is read from the first line of the file.
timestampFormat, timeFormat, dateFormat
type: String
default: yyyy-MM-dd HH:mm:ss, HH:mm:ss, yyyy-MM-dd
Defines the format from which columns of type Timestamp, Time and Date are parsed. See the Java SimpleDateFormat documentation for timestamp patterns.
timeZoneName
type: String
default: UTC
The time zone of Timestamp columns. To use the time zone of the computer, set this to the value returned by the method java.util.TimeZone.getDefault().getID().
trimHeaders
type: Boolean
default: True
If True, leading and trailing whitespace is trimmed from each column name in the header line. Column names inside quotes are not trimmed.
trimValues
type: Boolean
default: False
If True, leading and trailing whitespace is trimmed from each column value in the file. Column values inside quotes are not trimmed.

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
  // property values containing special characters).
  Connection conn2 = DriverManager.getConnection("jdbc:relique:csv:" + args[0] + "?" +
    "separator=" + URLEncoder.encode("|", "UTF-8") + "&" +
    "quotechar=" + URLEncoder.encode("'", "UTF-8") + "&" +
    "fileExtension=.txt" + "&" +
    "suppressHeaders=true");
    

Building From Source


To checkout and build the latest CsvJdbc source code, use the following commands (git and Maven must first be installed).

git clone git://git.code.sf.net/p/csvjdbc/code csvjdbc
cd csvjdbc
mvn install
cd target
dir csvjdbc*.jar

Building With Maven


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>1.0.19</version>
    </dependency>
  </dependencies>

License


CsvJdbc is released under the GNU Lesser General Public License (LGPL).

Last modified: 18 April 2014 by Simon Chenery (simoc)