Embedded Files
Reading a File
Reading a File
This example assumes a text file called dblist.txt exists in /u01/dba/java/source...
import java.io.*;
class filereadtest {
public static void main (String args []) throws IOException
{
String file_name = "/u01/dba/java/source/dblist.txt";
BufferedReader bufferedReader = new BufferedReader(new FileReader(file_name));
String line = "x";
while (line != null)
{
while ((line = bufferedReader.readLine()) != null)
{
System.out.println(line);
}
}
}
}
Check for Empty Set
Check for Empty Set
public class Main { public static void main(String[] args) { String myStr1 = "Hello"; String myStr2 = ""; System.out.println(myStr1.isEmpty()); System.out.println(myStr2.isEmpty()); }}
falsetrue
Example - Running different SQL for different database versions
Example - Running different SQL for different database versions
Scenario... Java code that runs SQL that should return a single row result set. If the SQL fails (due to something like a missing column) then run alternate SQL that uses a different query to populate the single row result set. If the SQL returns an empty set then force an exception so that the alternate SQL is run.
import java.sql.*class OraVersion{ public static void main (String args []) throws SQLException, IOException { DriverManager.registerDriver (new oracle.jdbc.driver.OracleDriver()); Connection conn = DriverManager.getConnection (fileline); Statement stmt = conn.createStatement(); String rversion = "";
try { \\ 12c Syntax ResultSet rset = stmt.executeQuery("SELECT r.version||'.'||r.bundle_id AS version \n"+ "FROM sys.registry$sqlpatch r \n"+ "WHERE action = 'APPLY' \n"+ "AND flags != 'NJJ' \n"+ "AND action_time = (SELECT MAX(action_time) \n"+ " FROM sys.registry$sqlpatch \n"+ " WHERE action = 'APPLY' \n"+ " AND flags != 'NJJ')"); while (rset.next()) { rversion = rset.getString("VERSION"); } } catch(SQLException se1) { try { // 11.2 Syntax ResultSet rset = stmt.executeQuery("SELECT SUBSTR(r.comments,5) AS version \n"+ "FROM sys.registry$history r, \n"+ "WHERE r.action = 'APPLY' \n"+ "AND r.action_time = (SELECT MAX(action_time) \n"+ " FROM sys.registry$history \n"+ " WHERE action = 'APPLY')"); while (rset.next()) { rversion = rset.getString("VERSION"); } // This check forces us of 11.1 syntax if 11.2 query returns empty set if (rhostnam.isEmpty()) { throw new SQLException("No result"); } } catch(SQLException se2) { try { // 11.1 syntax ResultSet rset = stmt.executeQuery("SELECT i.version AS version, \n"+ "FROM v$instance i"); while (rset.next()) { rversion = rset.getString("VERSION"); } } catch(SQLException se3) { System.out.println("ERROR: unable to retrieve version"); } } } finally { if (stmt!=null) stmt.close(); } }}
try { \\ 12c Syntax ResultSet rset = stmt.executeQuery("SELECT r.version||'.'||r.bundle_id AS version \n"+ "FROM sys.registry$sqlpatch r \n"+ "WHERE action = 'APPLY' \n"+ "AND flags != 'NJJ' \n"+ "AND action_time = (SELECT MAX(action_time) \n"+ " FROM sys.registry$sqlpatch \n"+ " WHERE action = 'APPLY' \n"+ " AND flags != 'NJJ')"); while (rset.next()) { rversion = rset.getString("VERSION"); } } catch(SQLException se1) { try { // 11.2 Syntax ResultSet rset = stmt.executeQuery("SELECT SUBSTR(r.comments,5) AS version \n"+ "FROM sys.registry$history r, \n"+ "WHERE r.action = 'APPLY' \n"+ "AND r.action_time = (SELECT MAX(action_time) \n"+ " FROM sys.registry$history \n"+ " WHERE action = 'APPLY')"); while (rset.next()) { rversion = rset.getString("VERSION"); } // This check forces us of 11.1 syntax if 11.2 query returns empty set if (rhostnam.isEmpty()) { throw new SQLException("No result"); } } catch(SQLException se2) { try { // 11.1 syntax ResultSet rset = stmt.executeQuery("SELECT i.version AS version, \n"+ "FROM v$instance i"); while (rset.next()) { rversion = rset.getString("VERSION"); } } catch(SQLException se3) { System.out.println("ERROR: unable to retrieve version"); } } } finally { if (stmt!=null) stmt.close(); } }}
Bibliography
Bibliography
https://www.geeksforgeeks.org/system-out-println-in-java/https://www.geeksforgeeks.org/difference-between-print-and-println-in-java/https://www.geeksforgeeks.org/java-io-printwriter-class-java-set-1/https://www.geeksforgeeks.org/io-bufferedwriter-class-methods-java/https://www.geeksforgeeks.org/printstream-println-method-in-java-with-examples/https://www.geeksforgeeks.org/redirecting-system-out-println-output-to-a-file-in-java/
Exception Handlinghttps://www.w3schools.com/java/java_try_catch.asphttps://stackoverflow.com/questions/6942624/how-can-i-throw-a-general-exception-in-java
isEmpty()https://www.w3schools.com/java/ref_string_isempty.asp
Exception Handlinghttps://www.w3schools.com/java/java_try_catch.asphttps://stackoverflow.com/questions/6942624/how-can-i-throw-a-general-exception-in-java
isEmpty()https://www.w3schools.com/java/ref_string_isempty.asp
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