2006 JavaOne SM Conference | Session BOF-0367 JDBC™Technology-based Metadata Recipes Mahmoud Parsian Server Architect LimeLife, Inc

2006 JavaOneSM Conference | Session BOF-0367

JDBC™Technology-based Metadata RecipesMahmoud ParsianServer ArchitectLimeLife, Inc.http://www.limelife.com

Session ID#: BOF-0367

2006 JavaOneSM Conference | Session BOF-0367 | 2

Learn how to use JDBC™ metadata in homogenous and heterogeneous database environments.

Goal of This Talk


Agenda: JDBC™ Metadata Recipes

What is metadata?What is Database metadata?What is JDBC metadata?What is a reverse engineering of a DB?Metadata in a homogenous environmentMetadata in a heterogeneous environment



What is “metadata”?What is Database metadata?What is JDBC metadata?What is a reverse engineering of a DB?Metadata in a homogenous environmentMetadata in a heterogeneous environment


What is Metadata? ● Metadata Definition● Metadata Examples● Database Metadata Examples● Purpose of Metadata


Metadata Definition Metadata is data about data, which provide

structured, descriptive information about other data.

Metadata (Greek: meta-+ Latin: data “information”), literally “data about data”, is information that describes another set of data.


Metadata Examples

Example-1: a library catalog card, which contains data about the contents and location of a book: It is data about the data in the book referred to by the card.


Metadata Examples: A Library Catalog CardA library catalog is an organized, searchable list of records

that identify, describe, and locate materials in one or more library collections. Each record includes information about the material, such as its:

● Author(s) ● Title ● Publisher ● Publication Date ● Subject Heading(s) ● Physical Appearance (size, number of pages, maps,

illustrations, etc.) ● Location within a collection


Database Metadata Examples

Example-1: what is the list of tables and views owned by database user Alex?

Example-2: what is the signature of a stored procedure called printPayroll?

Example-3: what is the list of SQL keywords supported by a Connection object?


Purpose of Metadata

The purpose of the metadata is to make database objects in the database more accessible to users and to provide basic information about the objects in the database's collection.

Each object within the database is described in a record by fields, such as:

● Table/View Names● Stored Procedure names & their signatures● Connection Properties● Result Set Properties



What is “metadata”?What is Database metadata? What is JDBC metadata?What is a reverse engineering of a DB?Metadata in a homogenous environmentMetadata in a heterogeneous environment


What is Database Metadata?

You can use database metadata to● Discover database schema and catalog information.● Discover database users, tables, views, and stored

procedures.● Understand and analyze the result sets returned by SQL

queries.● Find out the table, view, or column privileges.● Determine the signature of a specific stored procedure in the

database.● Identify the primary(PK)/foreign(FK) keys for a given table.



What is metadata?What is Database metadata? What is JDBC metadata?What is a reverse engineering of a DB?Metadata in a homogenous environmentMetadata in a heterogeneous environment


What is JDBC™ Metadata?

Metadata as Low-Level ObjectsMetadata API

● DatabaseMetaData● ResultSetMetaData● ParameterMetaData● DriverPropertyInfo● RowSetMetaData

Metadata Examples


Metadata as Low-Level Objects


Metadata API● java.sql.DatabaseMetaData● java.sql.ResultSetMetaData● java.sql.ParameterMetaData● java.sql.DriverPropertyInfo● javax.sql.RowSetMetaData


Metadata Example-1Are Transactions Supported?java.sql.Connection conn = getConnection(“datasourceName”);java.sql.DatabaseMetaData meta = conn.getMetaData();if (meta == null) {

// metadata not supported by the Driver}else {

// Check to see if transactions are supportedif (meta.supportsTransactions()) {

// Transactions are supported}else {

// Transactions are not supported}

}


Metadata Example-2:What Are the Table Names for a Database?private static final String[] DB_TABLE_TYPES = { "TABLE" };private static final String[] DB_VIEW_TYPES = { "VIEW" };java.sql.Connection conn = getConnection(“datasourceName”);java.sql.DatabaseMetaData meta = conn.getMetaData();java.sql.ResultSet tables = null;java.sql.ResultSet views = null;…views = meta.getTables(null, null, null, DB_VIEW_TYPES); tables = meta.getTables(null, null, null, DB_TABLE_TYPES);while (tables.next()) {

String tableName = rs.getString(“TABLE_NAME”);}





What is a reverse engineering of a DB?

Generate the original schema from database metadata:

Examples: ● Torque: an object-relational mapper for Java● SQL2Java:object-relational mapping tool.● Abator: a code generator for the iBATIS data

mapping framework





Metadata in a Homogenous EnvironmentSchema means the same for all DBs

Catalog means the same for all DBs

MySQL

MySQL Driver

MySQL MySQL

DriverManager

Connection DatabaseMetaData





Metadata in a Heterogeneous Environment● Metadata in a Heterogeneous

Environment● Solving the Metadata Problem● Example-1: getDBNames()● Example-2: getTableNames()● DB Vendor Matters


Metadata in a Heterogeneous EnvironmentSchema does NOT mean the same for all DBs

Catalog does NOT mean the same for all DBs

MySQL

MySQL Driver

Oracle PostgreSQL

DriverManager

Connection DatabaseMetaData

DB2

Oracle Driver PostgreSQL Driver DB2 Driver


Solving the Metadata Problem in a Heterogeneous Environmentimport java.sql.Connection;

public class ConnectionObject {

private Connection conn = null;

private String databaseVendor = null;

ConnectionObject(Connection conn,

String databaseVendor) {

this.conn = conn;

this.databaseVendor = databaseVendor;

}

… get()/set() methods

}


Example-1: getDBNames()

How do we get database names?● Oracle treats “schema” as a database name,● MySQL treats “catalog” as a database name. ● In order to get the name of databases from

Oracle, you must use DatabaseMetaData.getSchemas()

● In order to get the name of databases from MySQL, you must use DatabaseMetaData.getCatalogs()


Example-1: getDBNames()public static ResultSet getDBNames(ConnectionObject conn)

throws SQLException {ResultSet dbNames = null;DatabaseMetaData meta = conn.getMetaData();if (conn.isOracle()) {

dbNames = meta.getSchemas();}else if (conn.isMySQL()) {

dbNames = meta.getCatalogs();}else {

…}

return dbNames;}


Example-2: getTableNames()● DatabaseMetaData.getTables() method returns

the table names for a given database connection object. ● The getTables() method works well for MySQL● The getTables() does NOT work well for Oracle

databases (in addition to user’s tables, it returns system tables, which are not needed)

● To get a list of user-defined tables and views, we use the Oracle’s metadata table called user_objects, which keeps track of objects (tables, views, ...) owned by the user. We may use the following SQL query:

select object_name from user_objectswhere object_type = 'TABLE';


Example-2: getTableNames()public static ResultSet getTableNames(ConnectionObject conn)

throws SQLException {ResultSet tableNames = null;DatabaseMetaData meta = conn.getMetaData();if (conn.isOracle()) {

tableNames = getOracleTableNames(conn); // cannot use metadata}else if (conn.isMySQL()) {

tableNames = meta.getTables(…);}else {

…}

return tableNames;}


DB Vendor Matters<?xml version='1.0'><databases>

<database id="db1“, dbVendor=“mysql”<url>jdbc:mysql://localhost/octopus</url><driver>org.gjt.mm.mysql.Driver</driver><username>root</username><password>mysql</password>...</database><database id="db2“, dbVendor=“oracle”<url>jdbc:oracle:thin:@localhost:1521:kitty</url><driver>oracle.jdbc.driver.OracleDriver</driver><username>scott</username><password>tiger</password>... </database> ...

</databases>


Summary● JDBC API enable us to get metadata● JDBC metadata can be used to develop

● GUI database applications● SQL Adapters and Connectors● Reverse engineer the whole database

● In using JDBC metadata, make sure to consider the “vendor” factor (this will make your DB applications to work in homogenous and heterogeneous environments)


For More Information● Metadata Definition: http://en.wikipedia.org/wiki/Metadata● JDBC™ Basics:

http://java.sun.com/docs/books/tutorial/jdbc/basics/● JDBC™ API Tutorial and Reference, Third Edition

By Maydene Fisher,…, Addison Wesley, 2003.● JDBC™ Metadata, MySQL and Oracle Recipes,

Mahmoud Parsian, Apress.com, 2006● Understanding JDBC™ Metadata by Kyle Brown

http://members.aol.com/kgb1001001/Articles/JDBCMetadata/JDBC_Metadata.htm

2006 JavaOneSM Conference | Session XXXX | 34

Q&AMahmoud [email protected]@yahoo.com

Documents

2006 JavaOne SM Conference | Session BOF-0367 JDBC™Technology-based Metadata Recipes Mahmoud Parsian Server Architect LimeLife, Inc