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3.10. What Is the JDBC View of a Database s Internal Structure
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The JDBC views a database in terms of catalog, schema, table, view, column, triggers, indexes, and stored procedures. The JDBC view of a database s internal structure appears in Figure 3-3.
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CHAPTER 3 DATABASE METADATA, PART 2
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Figure 3-3. Internal structure of a database
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From the JDBC view of a database: A database server has several catalogs (such as database partitions and databases). A catalog has several schemas (these are user-specific namespaces). A schema has several database objects (tables, views, triggers, indexes, stored procedures, etc.). The java.sql.DatabaseMetaData interface has methods for discovering all the catalogs, schemas, tables, views, indexes, and stored procedures in the database server. These methods return a ResultSet, which can be traversed for getting the desired information. public static void main(String[] args) throws Exception { // Load the database driver - in this case, we // use the Jdbc/Odbc bridge driver. Connection conn = null; try { Class.forName("sun.jdbc.odbc.JdbcOdbcDriver"); // Open a connection to the database conn = DriverManager.getConnection( "[jdbcURL]", "[login]", "[passwd]"); // Get DatabaseMetaData DatabaseMetaData dbmd = conn.getMetaData(); // Get all Catalogs System.out.println("\nCatalogs are called '" + dbmd.getCatalogTerm() + "' in this RDBMS."); processResultSet(dbmd.getCatalogTerm(), dbmd.getCatalogs());
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CHAPTER 3 DATABASE METADATA, PART 2
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// Get all Schemas System.out.println("\nSchemas are called '" + dbmd.getSchemaTerm() + "' in this RDBMS."); processResultSet(dbmd.getSchemaTerm(), dbmd.getSchemas()); // Get all Table-like types System.out.println("\nAll table types supported in this RDBMS:"); processResultSet("Table type", dbmd.getTableTypes()); } finally { // Close the Connection object } } public static void processResultSet(String preamble, ResultSet rs) throws SQLException { // Printout table data while(rs.next()) { // Printout System.out.println(preamble + ": " + rs.getString(1)); } // Close database resources rs.close(); }
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3.11. Does a Database Support Batching
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With batch updating, a set of SQL statements is assembled and then sent to the database for execution. Batch updating can improve performance if you send lots of update statements to the database. According to Sun s JDBC Tutorial (http://java.sun.com/docs/books/tutorial/ jdbc/jdbc2dot0/batchupdates.html), A batch update is a set of multiple update statements that is submitted to the database for processing as a batch. Sending multiple update statements to the database together as a unit can, in some situations, be much more efficient than sending each update statement separately. This ability to send updates as a unit, referred to as the batch update facility, is one of the features provided with the JDBC 2.0 API. Determine Whether a Database Supports Batching /** * Check to see if database supports batching. * @param conn connection object to the desired database * @return true if database supports batching. */ public static boolean supportsBatching(java.sql.Connection conn) { if (conn == null) { return false; }
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CHAPTER 3 DATABASE METADATA, PART 2
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try { DatabaseMetaData dbmd = conn.getMetaData(); if (dbmd == null) { // database metadata not supported return false; } if (dbmd.supportsBatchUpdates()) { // batching is supported return true; } else { // batching is not supported return false; } } catch (Exception e) { // handle the exception return false; } } Making Batch Updates Next I ll provide an example that will perform batch updates. This example will be accomplished in several steps: Step 1: Setting up the database Step 2: Developing a sample program for batch updating Step 3: Running the sample program Step 4: Verifying the database results Step 5: Discussing the solution Step 1: Setting up the Database Let s create a simple table, which will perform batch updates. $ mysql --user=root --password=root Welcome to the MySQL monitor. Commands end with ; or \g. Your MySQL connection id is 4240 to server version: 4.0.18-nt mysql> use octopus; Database changed mysql> create table batch_table( -> id varchar(5) not null, -> name varchar(10) not null, -> primary key(id) -> );
CHAPTER 3 DATABASE METADATA, PART 2
Query OK, 0 rows affected (0.05 sec) mysql> describe batch_table; +-------+-------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+-------------+------+-----+---------+-------+ | id | varchar(5) | | PRI | | | | name | varchar(10) | | | | | +-------+-------------+------+-----+---------+-------+ 2 rows in set (0.01 sec) Step 2: Developing a Sample Program for Batch Updating Here is the solution for batch updates. For discussion purposes, I have added line numbers. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 import import import import import import java.sql.Connection; java.sql.Statement; java.sql.ResultSet; java.sql.SQLException; java.sql.BatchUpdateException; jcb.util.DatabaseUtil;
public class TestBatchUpdate { public static Connection getConnection() throws Exception { String driver = "org.gjt.mm.mysql.Driver"; String url = "jdbc:mysql://localhost/octopus"; String username = "root"; String password = "root"; Class.forName(driver); // load MySQL driver return DriverManager.getConnection(url, username, password); } public static void main(String args[]) { ResultSet rs = null; Statement stmt = null; Connection conn = null; try { conn = getConnection(); stmt = conn.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE, ResultSet.CONCUR_UPDATABLE); conn.setAutoCommit(false); stmt.addBatch("INSERT INTO batch_table(id, name) "+ "VALUES('11', 'Alex')"); stmt.addBatch("INSERT INTO batch_table(id, name) "+ "VALUES('22', 'Mary')"); stmt.addBatch("INSERT INTO batch_table(id, name) "+ "VALUES('33', 'Bob')");
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