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Using the Mimer JDBC Driver


This chapter explains how to load the Mimer JDBC driver and how to connect to a Mimer SQL database. It also contains JDBC application examples and discusses driver characteristics.

Loading a Driver

To use the Mimer JDBC driver, it must be loaded into the Java environment. The Java environment locates a driver by a search along the class path, defined in the CLASSPATH environment variable.

The CLASSPATH environment variable informs the Java environment where to find Java class files, such as the Mimer JDBC drivers.

The Mimer JDBC driver jar file, including the directory specification, should be added to the Java class path, as can be seen in the following examples:

UNIX: # echo $CLASSPATH
CLASSPATH=.:/usr/lib/mimjdbc3.jar

Win: % set CLASSPATH=.;D:\MIMJDBC3.JAR

Besides defining the CLASSPATH environment variable explicitly, it can also be defined for a specific session when executing the application. For example:

 java -classpath /usr/lib/mimjdbc3.jar JdbcApplication

Connecting the Traditional Way

The connection provides the link between the application and the Mimer SQL database server. To make a connection using the DriverManager class requires two operations, i.e. loading the driver and making the connection.

The class name of the Mimer JDBC Driver is:

 com.mimer.jdbc.Driver
 

The class name of the Mimer JDBC Trace Driver is:

 com.mimer.jtrace.Driver
 

The jar file referenced in the CLASSPATH determines which driver is loaded.

A driver can be explicitly loaded using the standard Class.forName method:

 import java.io.*;
 import java.sql.*;
 
 ...
 
 try {
         Class.forName("com.mimer.jdbc.Driver");
 
     } catch (java.lang.ClassNotFoundException cnf) {
         System.err.println("JDBC driver not found");
         return;
     }
 

Alternatively, DriverManager, when it initializes, looks for a jdbc.drivers property in the system properties. The jdbc.drivers property is a colon-separated list of drivers.

The DriverManager attempts to load each of the named drivers in this list of drivers. The jdbc.drivers property can be set like any other Java property, by using the -D option:

 java -Djdbc.drivers=com.mimer.jdbc.Driver class
 

The property can also be set from within the Java application or applet:

 Properties prp = System.getProperties();
 prp.put("jdbc.drivers",
            "com.mimer.jdbc.Driver:com.mimer.jtrace.Driver");
 System.setProperties(prp);
 
Note: Neither of the mechanisms used to load the driver specify that the application will actually use the driver. The driver is merely loaded and registered with the DriverManager.

Connecting With URL

To make the actual database connection, a URL string is passed to the DriverManager.getConnection method in the JDBC management layer.

The URL defines the data source to connect to. The JDBC management layer locates a registered driver that can connect to the database represented by the URL.

URL Syntax

The Mimer JDBC drivers support the following URL syntax:

 jdbc:mimer:[protocol:][URL-field-list][property-list]
 

URL-field-list options can be combined with property-list options.

Protocol

If a protocol is specified, the driver will load the mimcomm JNI library and use native routines to connect to the database. If the protocol is not specified (or is an empty string), no JNI library will be loaded and a TCP/IP connection will be made using standard Java network packages in you Java runtime.

Supported protocols include:

protocol
Explanation
decnet
Use Decnet to connect to a remote server (VMS only).
local
Use shared memory communication to a server that runs on your local machine. This protocol is often much faster than TCP/IP-based communication.
rapi
Use the RAPI protocol to connect to mobile devices (Windows only).
native tcp
Connect to the server using TCP/IP, but through the mimcomm JNI library.
tcp
Connect to the server using the Java TCP/IP stack.
single
Open a database in SINGLE mode.

URL-field-list

All fields in the URL-field-list are optional.

The database server host computer, with or without a user specification, is introduced by // and the database name is introduced by /, like:

 [//[user[:password]@]serverName[:portNumber]] [/databaseName]
 

A Connection object is returned from the getConnection method, for example:

 String url = "jdbc:mimer://MIMER_ADM:admin@localhost/ExampleDB";
 Connection con = DriverManager.getConnection(url);
 

Alternatively, the getConnection method allows the user name and password to be passed as parameters:

 url = "jdbc:mimer://localhost/ExampleDB";
 con = DriverManager.getConnection(url, "MIMER_ADM", "admin");
Property-list

The property-list for the Mimer JDBC Driver is optional. The list is introduced by a leading question mark ? and where there are several properties defined they are separated by ampersands &, like:

 ?property=value[&property=value[&property=value]]
 

The following properties are supported:

Property
Explanation
databaseName
Name of database server to access
user
User name used to log in to the database
password
Password used for the login
serverName
Computer on which the database server is running, the default is localhost
protocol
The protocol to use when connecting. If set, load the mimcomm JNI library. If empty, use standard Java TCP/IP support.
portNumber
Port number to use on the database server host, the default is 1360
program
Program name used to log in to the database
programPwd
Password used for the program

The following example demonstrates a connection using the driver properties:

 url = "jdbc:mimer:?databaseName=ExampleDB"
                + "&user=MIMER_ADM"
                + "&password=admin"
                + "&serverName=srv2.mimer.com";
 con = DriverManager.getConnection(url);
 

Alternatively a java.util.Properties object can be used:

 Properties dbProp = new Properties();
 
 dbProp.put("databaseName", "ExampleDB");
 dbProp.put("user", "MIMER_ADM");
 dbProp.put("password", "admin");
 con = DriverManager.getConnection("jdbc:mimer:", dbProp);
 

Elements from the URL-field-list and the property-list can be combined:

 url = "jdbc:mimer:/ExampleDB"
                + "?user=MIMER_ADM"
                + "&password=admin";
 

The DriverPropertyInfo class is available for programmers who need to interact with a driver to discover the properties that are required to make a connection. This enables a generic GUI tool to prompt the user for the Mimer SQL connection properties:

 Driver drv;
 DriverPropertyInfo [] drvInfo;
 
 drv = DriverManager.getDriver("jdbc:mimer:");
 drvInfo = drv.getPropertyInfo("jdbc:mimer:", null);
 for (int i = 0; i < drvInfo.length; i++) {
     System.out.println(drvInfo[i].name + ": " + drvInfo[i].value);
 }
 

After connecting to the database, all sorts of information about the driver and database is available through the use of the getMetadata method:

 DatabaseMetaData dbmd;
 
 dbmd = con.getMetaData();
 
 System.out.println("Driver      " + dbmd.getDriverName());
 System.out.println("    Version " + dbmd.getDriverVersion());
 System.out.println("Database    " + dbmd.getDatabaseProductName());
 System.out.println("    Version " + dbmd.getDatabaseProductVersion ());
 con.close();
 

The close method tells JDBC to disconnect from the Mimer SQL database server. JDBC resources are also released.

It is usual for connections to be explicitly closed when no longer required. The normal Java garbage collection has no way of freeing external resources, such as the Mimer SQL database server.

Connecting the J2EE Way

Along with J2EE came a new way for JDBC drivers to connect to database servers. Instead of requesting connections through the java.sql.DriverManager class, applications should connect using the javax.sql.DataSource, com.mimer.jdbc.MimerConnectionPoolDataSource or com.mimer.jdbc.MimerXADataSource interfaces.

Deploying Mimer JDBC in JNDI

The Mimer DataSource class is com.mimer.jdbc.MimerDataSource. When applications are deployed within the J2EE environment, a properly initiated MimerDataSource object should be stored in JNDI for the application server to retrieve at runtime. Application servers may use the JavaBean interface to obtain configuration parameters for MimerDataSource objects.

These are the DataSource attributes recognized by the Mimer JDBC drivers:

DataSource Attributes
Description
serverName
The computer on which the database server is running, the default is localhost
portNumber
The port number to use on the server host, the default is 1360
description
A textual description
databaseName
The name of the database on the server (required)
user
User name
password
Password
protocol
The protocol to use when connecting via the mimcomm JNI library
service
The service to connect to. This field plays the same role as the portNumber field, but any string can be used for protocols that don't use integer-valued port numbers (such as Decnet or named pipes). If a service value is specified, any portNumber value is ignored.

See sample programs further down for programming examples.

Deploying Mimer JDBC in a Connection Pool

Mimer JDBC may be deployed in J2EE compliant connection pools.

When deploying Mimer JDBC in a connection pool, the class com.mimer.jdbc.MimerConnectionPoolDataSource should be used. This class features the same attributes as described above for com.mimer.jdbc.MimerDataSource.

Deploying Mimer JDBC in Distributed Transaction Environments

Mimer JDBC may be used in J2EE compliant distributed transaction environments.

When deploying Mimer JDBC to be used in distributed transactions, the class com.mimer.jdbc.MimerXADataSource should be used. Whenever connections are created using this factory class, Mimer SQL may cooperate in transactions with any other XA compliant database server.

Read more about Mimer SQL and distributed transactions in Mimer SQL Programmer's Manual.

Error Handling

Error handling is taken care of by using the classes SQLException and SQLWarning.

The Mimer JDBC specific error codes are in the range -22000 to -22999. When using Java, the error message is always included in the exception that is thrown.

To get the complete and accurate list of error codes, execute the following command:

 $ java com.mimer.jdbc.Driver -errors

The Class SQLException

The SQLException class provides information relating to database errors. Details include a textual description of the error, an SQLState string, and an error code. There may be a number of SQLException objects for a failure.

 try {
 
 ...
 
 } catch(SQLException sqe) {
     SQLException stk;
 
     stk = sqe;   // Save initial exception for stack trace
 
     System.err.println("\n*** SQLException:\n");
     while (sqe != null) {
         System.err.println("Message:     " + sqe.getMessage());
         System.err.println("SQLState:    " + sqe.getSQLState());
         System.err.println("NativeError: " + sqe.getErrorCode());
         System.err.println();
 
         sqe = sqe.getNextException();
     }
 
     stk.printStackTrace(System.err);
 }

The Class SQLWarning

The SQLWarning class provides information relating to database warnings. The difference between warnings and exceptions is that warnings, unlike exceptions, are not thrown.

The getWarnings method of the appropriate object (Connection, Statement or ResultSet) is used to determine whether warnings exist.

Warning information can be retrieved using the same mechanisms as in the SQLException example above but with the method getNextWarning retrieving the next warning in the chain:

 con = DriverManager.getConnection(url);
 checkSQLWarning(con.getWarnings());
 
 ...
 
 private static boolean checkSQLWarning( SQLWarning sqw )
 throws SQLException {
     boolean rc = false;
 
     if (sqw != null) {
         rc = true;
 
         System.err.println("\n*** SQLWarning:\n");
         while (sqw != null) {
             System.err.println("Message:     " + sqw.getMessage());
             System.err.println("SQLState:    " + sqw.getSQLState());
             System.err.println("NativeError: " + sqw.getErrorCode());
             System.err.println();
 
             sqw = sqw.getNextWarning();
         }
     }
 
     return rc;
 }

Viewing Driver Characteristics

By using the java com.mimer.jdbc.Driver command, you can view characteristics of a specific driver and the current environment:

 java com.mimer.jdbc.Driver options
 

The options available are:

:
Option
Description
-version
Display driver version
-sysprop
Display all system properties
-errors
List all JDBC error codes
-ping url
Test the database at the specified url
-mimcomm
Load the mimcomm JNI library and show its version number. Displays informational messages to help fix any problems.

The following is an example that uses the -version option:

 java com.mimer.jdbc.Driver -version
 Mimer JDBC driver version 3.31
 

Used without any arguments, the command will display usage information.

The mimcomm JNI library

The Mimer JDBC driver can be used in a 100% native Java environment. In this case, the connection to a Mimer database server is done by the TCP/IP support included in the Java platform.

However, it is also possible to load an external library called mimcomm that includes support for all the communication protocols available on the particular platform. Please note that the mimcomm library may not be available on platforms that don't have a recent version of Mimer SQL installed.

The name of the mimcomm library varies between platforms. It is called mimcomm.dll on Windows, libmimcomm.so on Unix and MIMCOMM.EXE on VMS.

When you install a Mimer SQL distribution, the mimcomm library will normally be installed in a place where the Java environment can find it. You can test this by using the -mimcomm switch as a command line argument to the JDBC driver:

 unix$ java -cp mimjdbc3.jar com.mimer.jdbc.Driver -mimcomm
 System.getProperty("java.library.path"):
 /opt/java/64/jdk1.6.0_31/jre/lib/amd64/server:/opt/java/64/jdk1.6.0_31/jre/
lib/amd64:/opt/java/64/jdk1.6.0_31/jre/../lib/amd64:/usr/java/packages/lib/
amd64:/usr/lib64:/lib64:/lib:/usr/lib
 
 System.loadLibrary("mimcomm"):
 
 mimcomm library Version: V1011A
 JNI parameter method:    JNI_COPY
 

When the JDBC driver loads the mimcomm library, it looks for the library in the path specified by the java.library.path system property. If the JDBC driver cannot find the library in the path listed, you should either move the mimcomm library to a directory listed in the path or consult your Java manual for instructions on how to change the java.library.path system property.

Java Program Examples

Below are a collection of small basic Java programs for different environments, showing a database connection and a simple database operation with some error handling.

JDBC Application Example

The example Java program below creates a result set containing all rows of the data dictionary view INFORMATION_SCHEMA.TABLES, then each row is fetched and displayed on standard output.

In this example, the user name and password are given separately using the DriverManager.getConnection method, i.e. not given in the URL specification.

The below example will work with the mimjdbc drivers.

 import java.sql.*;
 
 class Example
 {
     public static void main(String[] args)
     {
         try {
             Class.forName("com.mimer.jdbc.Driver");
             String url = "jdbc:mimer://my_node.mimer.se/customers";
             Connection con = DriverManager.getConnection(url,
                                                          "SYSADM","SYSPW");
             Statement stmt = con.createStatement();
             String sql = "select TABLE_SCHEMA,TABLE_NAME,TABLE_TYPE
                           from INFORMATION_SCHEMA.TABLES";
             ResultSet rs = stmt.executeQuery(sql);
             while (rs.next()) {
                 String schema = rs.getString(1);
                 String name = rs.getString(2);
                 String type = rs.getString(3);
                 System.out.println(schema + "  " + name + "  " + type);
             }
             rs.close();
             stmt.close();
             con.close();
         } catch (SQLException e) {
             System.out.println("SQLException!");
             while (e != null) {
                 System.out.println("SQLState  : " + e.getSQLState());
                 System.out.println("Message   : " + e.getMessage());
                 System.out.println("ErrorCode : " + e.getErrorCode());
                 e = e.getNextException();
                 System.out.println("");
            }
         } catch (Exception e) {
             System.out.println("Other Exception");
             e.printStackTrace();
         }
     }
 }
 

Another way to provide connection properties is to supply a java.util.Properties object to the DriverManager.getConnection method.

JDBC Application Example for J2EE

This example Java program deploys a com.mimer.jdbc.MimerDataSource in a file system JNDI repository. Note that the file system JNDI repository have to be downloaded from Sun. It is available for download at http://java.sun.com/products/jndi/serviceproviders.html. At this site, several other service providers may be downloaded as well.

 import javax.sql.*;
 import java.sql.*;
 import javax.naming.*;
 import javax.naming.directory.*;
 import java.util.Hashtable;
 
 public class RegisterJNDI
 {
     public static void main(String argv[])
     {
         try {
             com.mimer.jdbc.MimerDataSource ds =
                 new com.mimer.jdbc.MimerDataSource();
 
             ds.setDescription("Our Mimer data source");
             ds.setServerName("my_node.mimer.se");
             ds.setDatabaseName("customers");
             ds.setPortNumber("1360");
             ds.setUser("SYSADM");
             ds.setPassword("SYSPW");
 
             // Set up environment for creating initial context
             Hashtable env = new Hashtable();
 
             env.put(Context.INITIAL_CONTEXT_FACTORY,
                     "com.sun.jndi.fscontext.RefFSContextFactory");
             env.put(Context.PROVIDER_URL, "file:.");
             Context ctx = new InitialContext(env);
 
             // Register the data source to JNDI naming service
             ctx.bind("jdbc/customers", ds);
 
         } catch (Exception e) {
             System.out.println(e);
             return;
         }
     }
 }
 

Once the data source is deployed, applications may connect using the deployed DataSource object. For instance like the below code snippet:

 Hashtable env = new Hashtable();
 env.put(Context.INITIAL_CONTEXT_FACTORY,
         "com.sun.jndi.fscontext.RefFSContextFactory");
 env.put(Context.PROVIDER_URL, "file:.");
 Context ctx = new InitialContext(env);
 DataSource ds = (DataSource)ctx.lookup("jdbc/customers");
 return ds.getConnection();

Using the Driver from Applets

The example Java applet below creates a result set containing all rows of the data dictionary view INFORMATION_SCHEMA.TABLES, then each row is fetched and displayed on standard output.

In this example, the user name and password are given separately using the DriverManager.getConnection method, i.e. not given in the URL specification.

The example will work with the mimjdbc drivers.

 import java.sql.*;
 import java.applet.*;
 import java.awt.*;
 
 public class ExampleApplet extends java.applet.Applet {
     public void init() {
         resize(1200, 600);
     }
 
     public void paint(Graphics g) {
         int row = 1;
         g.drawString("Listing tables:", 20, 10 * row++);
         try {
             Class.forName("com.mimer.jdbc.Driver");
             String url = "jdbc:mimer://my_node.mimer.se/customers";
             Connection con = DriverManager.getConnection(url, "SYSADM",
                                                          "SYSPW");
             Statement stmt = con.createStatement();
             String sql = "select TABLE_SCHEMA,TABLE_NAME,TABLE_TYPE
                           from INFORMATION_SCHEMA.TABLES";
             ResultSet rs = stmt.executeQuery(sql);
             while (rs.next()) {
                 String schema = rs.getString(1);
                 String name = rs.getString(2);
                 String type = rs.getString(3);
                 g.drawString(schema + "  " + name + "  " + type, 50,
                              10 * row++);
             }
             rs.close();
             stmt.close();
             con.close();
         } catch (SQLException e) {
             g.drawString("SQLException!", 20, 10 * row++);
             while (e != null) {
                 g.drawString("SQLState  : " + e.getSQLState(), 20,
                              10 * row++);
                 g.drawString("Message   : " + e.getMessage(), 20,
                              10 * row++);
                 g.drawString("ErrorCode : " + e.getErrorCode(), 20,
                              10 * row++);
                 e = e.getNextException();
                 g.drawString("", 20, 10*row++);
             }
         } catch (Exception e) {
             g.drawString("Other Exception!", 20, 10 * row++);
             g.drawString(e.toString(), 20, 10 * row++);
         }
     }
 }

Executing the Java Applet Example

To use a Mimer JDBC Driver in a Java applet, copy the driver jar file to the directory containing the applet's Java classes.

This directory must be accessible to the Web server. The driver jar file name should be given as the applet tag's ARCHIVE parameter in the HTML file. For example:

 <html>
  <head>
   <title> The Example Applet
  </head>
  <body>
  Example Applet:
   <applet archive="mimjdbc3.jar"
           code="ExampleApplet.class"
           width=800
           height=600>
   </applet>
  </body>
 </html>
 

You execute the applet by accessing the HTML file from a browser, for example:

 http://my_node/ExampleApplet.html
 
Note: There is a security restriction for Java applets, which states that a network connection can only be opened to the host from which the applet itself was downloaded. This means that both the Web server distributing the applet code and the database server must reside on the same host computer.


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