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CS4273: Distributed System Technologies and Programming I
Lecture 8: Java Database Connection (JDBC)
Java DataBase Connections (JDBC)
JDBC driver
• A JDBC driver is located in cslab’s dir:
/usr/local/jt6/lib/mysql-connector-java-5.1.7-bin.jar
• You can either:
copy the zipped file to your local directory and unzip it:
> jar xvf mysql-connector-java-5.1.7-bin.jar
or
make a link from directory “com” in your local dir to the system JDBC
driver.
• A brief manual of MySQL JDBC in CSlab can be found at:
http://personal.cs.cityu.edu.hk/jdemo/
2
JDBC Structure
Java applications
JDBC API
JDBC driver manager
JDBC driver API
JDBC/ODBC
Bridge
Vendor’s
JDBC driver
ODBC
driver
database
database
3
2-Tier’s Structure
Web server site
applet
(proxy):
4040
JDBC
DBMS
system
4
3-Tiers Structure
Web server site
applet
HTTP
server
your CGI
server
DBMS
system
5
Demonstration of using MySQL in Cslab
Access MySQL interactive interface:
mysql -hhostname -uusername -ppasswd
e.g.
% mysql -hjserv -ujdemo -papple1
(jserv is the host name of DBMS, jdemo the user name and
apple1 the password.)
> use db_jdemo; // set database to db_jdemo
> select * from COFFEES;
……
6
Demonstration of using MySQL in Cslab (Cont.)
More SQL statements
> show tables;
// list all the table
> help;
> help contents;
> select * from myCOFFEES;
> drop table myCOFFEES;
> exit;
// quit the mysql interface
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Java applications and DBMS using JDBC
Java
Application
JDBC
DBMS
Note: no proxy is needed in this case.
8
JDBC: Java applications and MySQL
import java.sql.*;
public class CreateCoffees {
public static void main(String args[]) {
String url =
“jdbc:mysql://jserv.cs.cityu.edu.hk:3306/
db_jdemo”;
Connection con;
Statement stmt;
String createString = "create table
myCOFFEES " +
"(COF_NAME varchar(32), " +
"SUP_ID int, " + "PRICE float, " +
"SALES int, " + "TOTAL int)";
try {
Class.forName("com.mysql.jdbc.Driver");
con = DriverManager.getConnection(url,
"jdemo", "apple1");
stmt = con.createStatement();
stmt.executeUpdate(createString);
stmt.close();
con.close();
} catch(SQLException e) {
System.err.println(e.getMessage()); }
}
}
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JDBC: Java applications and MySQL (select)
import java.sql.*;
public class SelectCoffees {
public static void main(String args[]) {
String url =
"jdbc:mysql://jserv.cs.cityu.edu.hk:3306
/db_jdemo”;
Connection con;
Statement stmt;
String query = "select COF_NAME, PRICE
from COFFEES";
try {
Class.forName("com.mysql.jdbc.Driver");
con = DriverManager.getConnection(url,
"jdemo", "apple1");
stmt = con.createStatement();
ResultSet rs = stmt.executeQuery(query);
while (rs.next()) { // loop on each row of "rs"
String s = rs.getString("COF_NAME");
float f = rs.getFloat("PRICE");
System.out.println(s + "
" + f);
}
stmt.close();
con.close();
} catch(SQLException e) {
System.err.println(e.getMessage()); }
}
}
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Steps of JDBC Connection
1.
Load driver manager
Class.forName("Driver’s name"), e.g.,
Class.forName("com.mysql.jdbc.Driver");
Class.forName("com.sybase.jdbc.SybDriver");
Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
Note: name components separated by ‘.’ are a dir path name, relative to the current directory.
2.
•
•
•
Make a connection to DBMS system
Database URL
A database URL specifies where the database is. The general syntax:
jdbc: subprotocol_name: other_stuff
The format of other_stuff depends on the subprotocol used, e.g.,
String url="jdbc:mysql://jserv.cs.cityu.edu.hk:3306/db_50704380"
String url = “jdbc:odbc://whitehouse.gov:5000/Cat”
String url = "jdbc:sybase:Tds:ntr10:4100";
Database Connection
Connection con = DriverManager.getConnection(url, usr, pswd);
e.g., con = DriverManager.getConnection(url, "jdemo", "apple1");
11
Steps of JDBC Connection (Cont.)
3. Create a statement object
• create a Statement object out of Connection object for every SQL
statement:
Statement stmt = con.createStatement();
4. Execute an SQL statement
• Two types of SQL statements: queries and updates
ExecuteQuery
ResultSet rs = stmt.executeQuery (“select * from books”);
or:
String query = “select * from books”;
ResultSet rs = stmt.executeQuery (query);
ExecuteUpdate
stmt.executeUpdate(createString);
(there is no return needed for update statements)
12
Steps of JDBC Connection (Cont.)
5.
•
•
Get results from DBMS
The execution of an sql query returns a
set of rows. Each row consists of
several attributes (fields):
ResultSet rs = stmt.executeQuery
(query);
Access Rows of a ResultSet
The basic loop for analyzing a result
set uses format:
while ( rs.next()) {
// rs.next pointers to the next row
analyze a row of the result set;
}
Access Attributes of a row
• Get the value of an attribute by methods
of format:
Xxx getXxx (int clmn_num) or
Xxx getXxx (String clmn_name)
e.g., String cofName = rs.getString(1) or
String cofName =
rs.getString(“COF_NAME”);
• There are many other getXxx methods:
int supId = rs.getInt (“SUP_ID”);
float price = rs.getDouble (“PRICE”);
…….
• For other types, please refer to JDBC
manual.
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JDBC Connection between Applet and DBMS
2-Tier Structure
1. Install a JDBC proxy at the web server site (“personal.cs.cityu”).
2. An applet makes a JDBC connection to DBMS via the proxy, bcs
applets can only connect to its home server.
3. The result type of a sql query is ResultSet (process them in the
same way as discussed before).
Web server site
applet
(proxy):
4040
JDBC
DBMS
system
14
An Example of 2 Tier Structure
(Applet – DBMS)
public class myapplet extends Applet implements Runnable {
private Vector queryResults;
public synchronized void start() {
if (worker == null) {
message = "Connecting to database";
worker = new Thread(this); worker.start(); }
}
public void run() {
String url = "jdbc:mysql:
//personal.cs.cityu.edu.hk:4040/db_jdemo ";
String query = "select COF_NAME, PRICE
from COFFEES";
try {
Class.forName("com.mysql.jdbc.Driver");
Vector results = new Vector();
con= DriverManager.
getConnection(url, "jdemo", "apple1");
stmt = con.createStatement();
ResultSet rs = stmt.executeQuery(query);
while (rs.next()) {// process rs row by row
String s = rs.getString("COF_NAME");
float f = rs.getFloat("PRICE");
String text = s + " " + f;
results.addElement(text);
}
stmt.close(); con.close();
setResults(results);
repaint();
} catch(SQLException e) {;}
}
15
Disadvantages of the 2-Tier Structure
1. Fat clients (applets).
2. Little flexibility on the security control to the DBMS
accesses.
16
3-Tiers Structure
Web server site
applet
HTTP
server
your CGI
server
DBMS
system
17
Applet design in 3-tier (interact with CGI)
1.
2.
3.
4.
make socket connection to HTTP server and start cgi-svr by POST method.
receive String lines from cgi-svr, one for each row of data, and put them into a Vector.
Vector results = new Vector();
while ((line = in.readLine())!=null)
results.addElement(line);
paint() extracts data rows from the vector by using an Enumerration object.
Enumeration enum = queryResults.elements();
Web server site
a) check if it’s the end of the object:
HTTP
enum.hasMoreElements();
applet
server
b) get the next element from the object:
String text = (String) enum.nextElement();
for each line of data, break it into attributes
CGI
(separated by “|”) by using an StringTokenizer object.
StringTokenizer st = new StringTokenizer(text, "|");
server
String cof_name = st.nextToken();
String cof_price = st.nextToken();
18
Applet in 3-tier JDBC
public class myapplet extends Applet implements
while (! in.readLine.equals("START_DATA"));
Runnable {
while ((line = in.readLine()) != null)
Thread worker; Vector queryResults;
if (line.length() > 0)
public synchronized void start() {
results.addElement(line);
......... worker.start();
in.close(); out.close();
}
return(results);
public void run() {
}
Vector results = CallCgiSvr();
public synchronized void paint(Graphics g) {
if (results != null) setResults(results);
g.drawString("Prices of coffee per pound: ", 5, 10);
}
int x = 5, y = 30;
Vector CallCgiSvr() {
Enumeration enum = queryResults.elements();
Vector results = new Vector();
while (enum.hasMoreElements()) {
String sdata = "START_QUERY";
String text = (String)enum.nextElement();
s = new Socket(“personal.cs.cityu.edu.hk",80);
StringTokenizer st = new StringTokenizer(text, "|");
in = new DataInputStream(s.getInputStream());
String cof_name = st.nextToken();
out = new PrintStream(s.getOutputStream());
String cof_price = st.nextToken();
out.println("POST /3tier/shellcgi.cgi HTTP/1.0\r");
g.drawString(cof_name, x, y);
out.println("Content-type: plain/text\r");
g.drawString(cof_price, x+140, y);
out.println("Content-length: "+ sdata.length()+
y = y + 15; }
"\r\r");
}
out.println(sdata+"\r");
19
CGI Program in 3-Tier JDBC
1. cgi-svr acts as a gateway between applet and DBMS. No more need of a proxy at the
web site.
2. cgi-svr gets requests from client via stdin, connects to DBMS by JDBC, executes
queries and receives results:
a) get query results of type ResultSet:
ResultSet rs = stmt.executeQuery (query);
b) analyze each row and make it a line. Attributes of a line are separated by “|”.
String s = rs.getString("COF_NAME");
float f = rs.getFloat("PRICE");
String text = s + "|" + f;
HTTP
applet
c) append the lines into a StringBuffer.
server
StringBuffer results = new StringBuffer();
results.append (text + "\n");
d) convert StringBuffer to a single string and send it to applet via stdout.
CGI
String line = results.toString();
DBM
server
outs.println(line); // outs is the stdout stream
20
CGI program in 3-Tier JDBC
class cgisvr {
public static void main(String[] args) {
String request, line;
try {
DataInputStream ins = new DataInputStream(System.in);
PrintStream outs = new PrintStream(System.out);
while ((request = ins.readLine()) != null) {
if (request.equals("START_QUERY")) {
line = ReqSql ();
outs.println(START_DATA); // a start token
outs.println(line); }} // send reply to applet
outs.close();
} catch (Exception e) { System.out.println("Error"+e);}
}
21
CGI program in 3-Tier JDBC (Cont.)
static String ReqSql() {
String url = "jdbc:mysql:
//jserv.cs.edu.hk:3306/db_jdemo ";
String query = "select COF_NAME,
PRICE from COFFEES";
StringBuffer results = new StringBuffer();
Class.forName("com.mysql.jdbc.Driver");
con= DriverManager.
getConnection(url, "jdemo", "apple1");
Statement stmt = con.createStatement();
ResultSet rs = stmt.executeQuery(query);
while (rs.next()) {
String s = rs.getString("COF_NAME");
float f = rs.getFloat("PRICE");
String text = s + "|" + f;
results.append(text + "\n");
}
stmt.close(); con.close();
return(results.toString());
}
22
Shell Script starting the Java Program
#!/bin/sh
echo Content-type: text/plain
Echo
#the java command must use full path!
/usr/local/jdk/bin/java cgisvr
23