Java DataBase Connectivity[tm] FAQs

1. Where can I find tutorials including beginners information?
   
2. Isn't there an existing FAQ for the Java DataBase Connectivity[tm] (JDBC[tm]) API?
   
3. Is there any information regarding JDBC 3.0?
   
4. Where can I get drivers for my database? What are driver types?
   
5. Where can I learn more about JDBC - courses and books, for example?
   
6. Please tell me about BLOBs/CLOBs in JDBC ...
   
7. I keep getting a java.lang.OutOfMemoryError...
   
8. How could I use a properties file - to connect to the database, for example?
   
9. Class not found problems...
   
10. Can I serialize Java[tm] objects into the database?
    
11. How can I catch and use SQL exceptions?
    
12. How can I identify a database using a JDBC URL?
    
13. I've heard of SQLj; what is it?
    
14. We have a JDBC problem and we are using ORACLE®...
    
15. Using ORACLE®, my updatable result set query cannot use "SELECT *"
    
16. Where can I find out about exisiting bugs and how can I report one?
    
17. Can I get Java Developer Support[sm] from Sun Microsystems?

We want to hear from you! Please send us your FEEDBACK.

1. Where can I find tutorials including beginners information?

Four tutorials here:
http://java.sun.com/products/jdbc/learning.html

Getting Started with the JDBC[tm] API
http://java.sun.com/j2se/1.3/docs/guide/jdbc/getstart/GettingStartedTOC.fm.html

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~Savepoint support
~Reuse of prepared statements by connection pools
~Connection pool configuration
~Retrieval of parameter metadata
~Retrieval of auto-generated keys
~Ability to have multiple open ResultSet objects
~Passing parameters to CallableStatement objects by name
~Holdable cursor support
~BOOLEAN data type
~Making internal updates to the data in Blob and Clob objects
~Retrieving and updating the object referenced by a Ref object
~Updating of columns containing BLOB, CLOB, ARRAY and REF types
~DATALINK/URL data type
~Transform groups and type mapping
~Relationship between the JDBC SPI (Service Provider Interface) and the Connector architecture
~DatabaseMetadata APIs

JDBC[tm] 3.0 shall ship with Java[tm] 2 Platform, Standard Edition (J2SE[tm]) version 1.4; you can download a pre-FCS release here.

The J2SE 1.4 SDK JDBC documents are available here:
http://java.sun.com/j2se/1.4/docs/guide/jdbc/index.html

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The types of drivers and Java[tm] 2 Platform, Enterprise Edition (J2EE[tm]) technology certified information are available from the "help" link under the appropriate section, as well as from the results sets.

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Courses:
http://suned.sun.com/ Books:
JDBC API TUTORIAL AND REFERENCE
http://java.sun.com/docs/books/jdbc/

JDBC Database Access with Java[tm]
http://java.sun.com/docs/books/jdbc/

Advanced Programming for the Java 2 Platform
http://developer.java.sun.com/developer/onlineTraining/Programming/JDCBook/

The Java Tutorial
http://java.sun.com/docs/books/javatutorial/third-edition.html

Four tutorials here:
http://java.sun.com/products/jdbc/learning.html

Getting started with the JDBC API
http://java.sun.com/j2se/1.3/docs/guide/jdbc/getstart/GettingStartedTOC.fm.html

These guides cover creating BLOBs/CLOBs, manipulating and storing the data.  Further information should also be available from the database vendor or the driver vendor.
For BLOBs information, see:
http://java.sun.com/j2se/1.4/docs/guide/jdbc/blob.html

For CLOBs information, see:
http://java.sun.com/j2se/1.4/docs/guide/jdbc/clob.html

There is also further information in the JDBC specifications. See JDBC 3.0 above.

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"We are reading in 90,000 rows and obtain a java.lang.OutOfMemoryError with no stack trace available"
The likely case here is that the rows are being stored in memory, for example in a Vector, or memory is being used during this execution.  It is a good idea to rethink what the code is supposed to achieve in this instance. Do you really need to read-in so many rows? Would it be better to write the rows to a file, one row at a time?

One suggestion is to analyse what the driver is capable of offering and find the best and most efficient way of achieving the code purpose.

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It may be necessary to make properties in the application flexible for different needs of users and changing environments, instead of hardcoding properties to require recompilation upon a change.  Descriptions of ways to accomplish this, along with code snippets can be found:
For J2SE 1.3/1.4 see:
    http://java.sun.com/docs/books/tutorial/essential/attributes/index.html

For J2SE 1.4 see:
    http://java.sun.com/j2se/1.4/docs/guide/lang/preferences.html

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Using Class.forName(...) etc. you receive a ClassNotFoundException.

Firstly, check that the class exists either in the JAR file or in the filesystem structure.  If no class file exists then it may be that the driver has not been built or extracted correctly.

Ensure that your classpath is set correctly including spelling of directories, paths and JAR file names.  You may also want to make sure that the current directory is also in your classpath by adding "." to the classpath.

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It is possible to store Java objects into a database.
The Java Tutorial's Serialisation section http://java.sun.com/docs/books/tutorial/essential/io/serialization.html
 provides a generic understanding of how objects can be stored - writing and reading from a stream.

"Storing Java Objects in a Database" guide provides information on how SQL and Java types are mapped.
http://java.sun.com/j2se/1.4/docs/guide/jdbc/getstart/mapping.html#999058

"Support for Storing Java Objects" provides a small informational note.
http://java.sun.com/j2se/1.4/docs/guide/jdbc/getstart/appendixA.html#1002502

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Here is a small snippet of code demonstrating how your Java program can handle the SQL exceptions generated from JDBC[tm] calls.

     try{
        ....
    }
    catch(SQLException sqle) {

        int errorcode = sqle.getErrorCode();

        Switch(errorcode) {

           case 1: System.out.println("Primary key violation"); break;
           case 2291: System.out.println("Integrity constraint violation");
            break;
           default:  System.out.println("Other violation " +
                sqle.getMessage());
        }
    }

A SQLException can have a list of the following exception objects:

getNextException -returns the next SQLException
getErrorCode - returns an integer error code
getMessage - returns a String error message

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jdbc:subprotocol:subname

    subprotocol - driver or type of database connectivity mechanism
    subname     - identifies the database

jdbc:namingService:dataSrcName

    namingService - the naming service should resolve the database name
        into a more specific name that can be used to connect to the real  database.

    This requires Java Naming Directory Interface(JNDI) and JDBC 2.0 standard extensions.

jdbc:odbc:dataSrcName[;attributeName=attributeValue]

    odbc subprotocol can also contain name-value pairs.

jdbc:subprotocol://hostname:port/subsubname

    This URL specifies that the database is on a remote server.

SQLj is a language for embedding static SQL in the Java[tm] programming language.  It is an alternative method, in addition to the JDBC API, to connect a Java application to a relational database.

You can combine the two  in the same program and you would still need a JDBC driver to connect to the database.

SQLj can be a better choice due  to smaller source programs, and because it does compile-time checking.

SQLj group
http://www.sqlj.org

Database Programming in SQLj
http://industry.java.sun.com/javaone/99/event/0,1768,616,00.html

ORACLE® SQLj resource
http://otn.oracle.com/tech/java/sqlj_jdbc/content.html

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An excellent reference source can be found in Oracle Technology Network(OTN), namely "Oracle JDBC Developer's Guide and Reference".

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This is a limitation of the ORACLE® driver as a workaround try:

SELECT mytable.* FROM TABLE mytable ...

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Firstly, check to see if the bug has or is being addressed here:
http://developer.java.sun.com/developer/bugParade/index.jshtml

If need be, report a new bug here:
http://java.sun.com/cgi-bin/bugreport.cgi/

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http://www.sun.com/developers/support
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