After completing this unit, you should be able to: Code connection-related statements within a JDBC application

Transcription

1 JDBC Programming I

2 Unit Objectives After completing this unit, you should be able to: Code connection-related statements within a JDBC application Code the necessary import statements for JDBC interfaces Embed INSERT, UPDATE, DELETE and simple SELECT statements in JDBC applications Write code to check for Warning and Exception conditions and understand the SQLCA Utilize parameter markers in JDBC application programs Process data that allows NULL values Understand database access security when using JDBC

3 What Is JDBC? Java API for executing SQL A set of classes and interfaces written in Java A vendor-neutral dynamic SQL interface Uses only dynamic SQL

4 JDBC Programming 1. Import appropriate Java packages and classes 2. Load appropriate JDBC driver 3. Connect to the database, specifying the location with a URL and using the db2 subprotocol 4. Pass SQL statements to the database 5. Receive results 6. Close the connection

5 Import Classes and Load Driver import java.sql.*; 1 import java.io.*; import java.lang.*; class MyJDBC { static { 2 try { Class.forName("COM.ibm.db2.jdbc.app.DB2Driver"); } catch (Exception e) { e.printstacktrace(); }

6 Connect to Database public static void main (String argv[]){ try { 1 Connection con = null; 2 String url = "jdbc:db2:sample"; if (argv.length == 0) 3 { con = DriverManager.getConnection(url); } else if (argv.length == 2) { String userid = argv[0]; String passwd = argv[1]; 4 con = DriverManager.getConnection(url,userid,passwd); } else { throw new Exception ("\n Usage: java MyJDBC[,username,password]\n");}

7 SELECT Statement 1 Statement stmt = con.createstatement(); 2 ResultSet rs = stmt.executequery ("SELECT EMPNO, LASTNAME " + " FROM TEMPL " + " WHERE SALARY > " ); 3 4 while ( rs.next() ) { System.out.println("empno = " + rs.getstring(1) + "lastname = " + rs.getstring(2) ); } rs.close(); stmt.close(); con.close(); } catch (Exception e) { 8 } e.printstacktrace();

8 UPDATE Statement 1 Statement updstmt = con.createstatement(); 2 int numrows = updstmt.executeupdate ("UPDATE TEMPL " + " SET LASTNAME = 'Stohl' " + " WHERE EMPNO = '000110' "); System.out.println("Number of rows updated " + numrows);

9 Using Parameter Markers - UPDATE 1 PreparedStatement pupd = con.preparestatement ("UPDATE TEMPL " + " SET SALARY =? " + " WHERE EMPNO =? "); pupd.setstring(1,argv[1]); pupd.setstring(2,argv[2]); int numrows = pupd.executeupdate(); System.out.println("Number of rows updated " + numrows); 5 pupd.close();

10 Insert Statement 1 String sql = null; sql = "INSERT INTO TEMPL (EMPNO, LASTNAME, SALARY)" 2 + "VALUES ('000110', 'Roth', 50000)", 3 stmt = con.createstatement(); 4 insertcount = stmt.executeupdate( sql );

11 Delete Statement String eno = "000110"; String mysql = null; mysql = "DELETE FROM TEMPL WHERE EMPNO =?"; psstmt = con.preparestatement (mysql); pstmt.setstring (1, eno); deletecount = psstmt.executeupdate();

12 Declaring Host Variables Language Definitions FLOAT GRAPHIC CHAR C FORTRAN DB2 REFERENCE LIBRARY Java VARCHAR DECIMAL COBOL INTEGER

13 Declaring Host Variables - Java Program Host variables follow normal Java variable syntax Host variable names are treated by DB2 as global to the source module in which they are defined

14 Declaration Considerations for Java CREATE TABLE SIMPLE (TITLE CHAR (20) NOT NULL, NUMBER SMALLINT NOT NULL ) private static String title; private static short number; sql = "SELECT TITLE FROM SIMPLE " + "WHERE NUMBER =?"; pstmt = con.preparestatement(sql); pstmt.setstring (1, number); ResultSet prs = pstmt.executequery(); While (prs.next()) { title = prs.getstring(1);}

15 DCLGEN Generate table declaration - db2dclgn (DCLGEN) Creates Structures for host variables Languages supported C, Java, COBOL, FORTRAN db2dclgn -D sample -T employee -L Java

16 Processing Null Values In all but Java, use Indicator variables In Java, compare the value of the host variable with Java null Java example: sql = "SELECT MGRNO FROM EMP";... String mgrno = rs.getstring(1); if (mgrno == null) { System.out.println ("\n MGRNO is null \n");}

17 Example of Using the wasnull() Method Statement stmt = con.createstatement(); ResultSet rs = stmt.executequery ("SELECT EMPNO, LASTNAME, EDLEVEL " + " FROM EMP " ); while ( rs.next() ) { String eno = rs.getstring(1); String lname = rs.getstring(2); short edlvl = rs.getshort(3); if ( rs.wasnull() ) { System.out.println ("\n Edlevel is null for EMPNO \n"); System.out.println (eno); } // end if else { System.out.println ("\n Edlevel is: \n"); System.out.println ( edlvl ); System.out.println ("\n For EMPNO = \n"); System.out.println (eno); } // end else

18 Passing NULL Value - Java Program sql = "UPDATE TEMPL SET PHONENO =? " + "WHERE EMPNO = '000110' "; stmt = con.preparestatement(sql); if (some condition) { stmt.setstring (1, null); } else { stmt.setstring (1, newphone); } updatecount = stmt.executeupdate();

19 Example of Using the setnull() Method sql = "UPDATE EMP SET EDLEVEL =? " + " WHERE EMPNO = ' ' "; pstmt = con.preparestatement( sql ); if ( some condition ) { pstmt.setnull (1, java.sql.types.smallint); } else { pstmt.setshort( 1, 16 ); } updatecount = pstmt.executeupdate();

20 Determining Success of SQL Statements DB2 provides information to the program on the success or failure of the SQL statement Java programs throw an SQLException Other host languages check the SQLCA SQLCODE and SQLSTATE can be checked to determine precise error

21 SQLCA - SQL Communication Area Program S Q L C A Information / SQLCODE Executable SQL DB2

22 SQLCA Codes CONDITION INTEGER SQLCODE CHAR(1) SQLWARNO REQUEST STATUS ERROR <0 FAILED WARNING >0 & <> 100 OR 'W' SATISFIED WITH SPECIAL CONDITION NOTFOUND +100 (MORE) DATA NOT FOUND SQLSTATE = "02000" SUCCESS 0 AND ' ' SUCCESS

23 SQLCODE and SQLSTATE SQLCODE detailed possibly platform dependent numeric SQLSTATE first two characters - general all five characters - more information not as detailed as SQLCODE, but not as platform dependent

24 SQLCA SQLERRD Third Element PROGRAM: SQLCA SQLCODE SQLWARN0 SQLERRD[2] NUMBER OF ROWS AFFECTED DB2 INSERT UPDATE DELETE REQUEST

25 Error Processing try { sql = "DELETE FROM TEMPL WHERE EMPNO = 999"; psstmt = con.preparestatement(sql); deletecount = psstmt.execute Update(); if (( SQLWarn = psstmt.getwarnings())!=null) { System.out.println ("\n Warning received on a DELETE \n");} } // end try catch (SQLException x) { if (x.getsqlstate().equals("42818")) { System.out.println ("\n Operand data types not compatible \n"); } // end if else { System.out.println ("\n Error deleting from TEMPL \n"); System.out.println ("\n Value of SQLCODE is: \n"); SQLCode = x.geterrorcode(); System.out.println (SQLCode); } // end else } // end catch

26 JDBC and Security JDBC DELETE FROM TEMPL WHERE ID = '123' USERA GRANT DELETE ON TABLE TEMPL TO USER USERA

27 Unit Summary Since completing this unit, you should be able to: Code connection-related statements within a JDBC application Code the necessary import statements for JDBC interfaces Embed INSERT, UPDATE, DELETE and simple SELECT statements in JDBC applications Write code to check for Warning and Exception conditions and understand th SQLCA Utilize parameter markers in JDBC application programs Process data that allows NULL values Understand database access security when using JDBC