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CHAPTER 3 MAKING DATABASE CONNECTIONS
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if (dbVendor.equalsIgnoreCase("mysql")) { return testConnection(conn, "select 1"); } else if (dbVendor.equalsIgnoreCase("oracle")) { return testConnection(conn, "select 1 from dual"); } else { return false; } } /** * Test Validity of a Connection * @param conn a JDBC Connection object * @param query a sql query to test against db connection * @return true if a given Connection object is a valid one; * otherwise return false. */ public static boolean testConnection(Connection conn, String query) { ResultSet rs = null; Statement stmt = null; try { stmt = conn.createStatement(); if (stmt == null) { return false; } rs = stmt.executeQuery(query); if (rs == null) { return false; } // Connection object is valid: you were able to // connect to the database and return something useful. if (rs.next()) { return true; } // there is no hope any more for the validity // of the Connection object return false; } catch(Exception e) { // something went wrong: connection is bad return false; } finally { // close database resources DatabaseUtil.close(rs); DatabaseUtil.close(stmt); } } public static void main(String[] args) { Connection conn = null;
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CHAPTER 3 MAKING DATABASE CONNECTIONS
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try { System.out.println("-- CheckJDBCInstallation begin --"); String dbVendor = args[0]; // get connection to a database System.out.println("dbVendor="+dbVendor); conn = VeryBasicConnectionManager.getConnection(dbVendor); System.out.println("conn="+conn); System.out.println("valid connection = "+ isValidConnection(conn, dbVendor)); System.out.println("-- CheckJDBCInstallation end --"); } catch(Exception e){ // handle the exception e.printStackTrace(); System.exit(1); } finally { // release database resources DatabaseUtil.close(conn); } }
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The following discussion breaks down the program: Lines 1 4: Import the required classes and interfaces from the java.sql package. Lines 16 56 : isValidConnection() accepts a Connection object and determines whether it is a valid Connection object. After making sure that the connection is not closed, it invokes the testConnection() method, which retrieves the minimum information after connecting to the database. Lines 65 99 : The testConnection() method tests the validity of a Connection object by executing a minimal SELECT statement. The validity check statement for MySQL is select 1 (no need to mention a table name). The validity check statement may differ from vendor to vendor. The validity check statement for Oracle is select 1 from dual. (In Oracle databases, dual is a table that is created by Oracle along with the data dictionary. It consists of exactly one column whose name is dummy and one record. The value of that record is X. The owner of dual is SYS, but the dual table can be accessed by every user.)
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To run the program, use this code for MySQL: $ mysql --user=root --password=root --default-character-set=utf8 Welcome to the MySQL monitor. Commands end with ; or \g. Your MySQL connection id is 3 to server version: 4.1.7-nt mysql> exit Bye $ javac CheckJDBCInstallation.java $ java CheckJDBCInstallation mysql -- CheckJDBCInstallation begin -dbVendor=mysql
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CHAPTER 3 MAKING DATABASE CONNECTIONS
conn=com.mysql.jdbc.Connection@8fce95 valid connection = true -- CheckJDBCInstallation end --
Running CheckJDBCInstallation for the Oracle Database
To run the program, use this code for Oracle: $ sqlplus scott/tiger SQL*Plus: Release 10.1.0.2.0 - Production on Wed Oct 27 17:11:41 2004 SQL> exit Disconnected from Oracle Database 10g Enterprise Edition Release 10.1.0.2.0 $ javac CheckJDBCInstallation.java $ java CheckJDBCInstallation oracle -- CheckJDBCInstallation begin -dbVendor=oracle conn=oracle.jdbc.driver.T4CConnection@341960 valid connection = true -- CheckJDBCInstallation end --
CHAPTER
Making Database Connections Using DataSource
Relativity teaches us the connection between the different descriptions of one and the same reality. Albert Einstein
n this chapter, you will learn how to make database connections using JDBC s DataSource object. The purpose of this chapter is to provide snippets, reusable code samples, and methods that deal with the Connection objects using the javax.sql.DataSource interface. When writing this chapter, I relied on JDK 1.4 and the final release of the JDBC 3.0 specification. This chapter s focus will be on answering the following question: how do you obtain a java.sql.Connection object from javax.sql.DataSource objects I can present this question in another way: what are the connection options This chapter will answer these questions, and for each case I will provide working code. To select data from tables/views, update columns in tables, create a new table in a database, or do anything useful with any database, you need a database connection (in JDBC, this is called java.sql.Connection). Typically, database access in any environment starts with the connection.
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