10 jdbc

© 2010 Marty Hall
Database Access
with JDBCOriginals of Slides and Source Code for Examples:Originals of Slides and Source Code for Examples:
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© 2010 Marty Hall
For live Java EE training, please see training courses
at http://courses.coreservlets.com/.at http://courses.coreservlets.com/.
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Taught by the author of Core Servlets and JSP, More
Servlets and JSP and this tutorial Available at public
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Overview
• Overview of JDBC technology
• JDBC design strategies
• Using Apache Derby (Java DB)
• Seven basic steps in using JDBC
• Using JDBC from desktop Java apps
• Using JDBC from Web apps
• Prepared statements (parameterized
d )commands)
• Meta data
Transaction control• Transaction control
5
© 2010 Marty Hall
Overview

JDBC Introduction
• JDBC provides a standard library for
i l i l d baccessing relational databases
– API standardizes
• Way to establish connection to database• Way to establish connection to database
• Approach to initiating queries
• Method to create stored (parameterized) queries
Th d t t t f lt (t bl )• The data structure of query result (table)
– Determining the number of columns
– Looking up metadata, etc.
– API does not standardize SQL syntax
• JDBC is not embedded SQL
– JDBC classes are in the java.sql packageJDBC classes are in the java.sql package
• Note: JDBC is not officially an acronym;
– Unofficially, “Java DataBase Connectivity” is commonly used7
On-line Resources
• Sun’s JDBC Site
– http://java.sun.com/javase/6/docs/technotes/guides/jdbc/
• JDBC Tutorial
h //j /d /b k / i l/jdb /– http://java.sun.com/docs/books/tutorial/jdbc/
• API for java.sql
http://java sun com/javase/6/docs/api/java/sql/– http://java.sun.com/javase/6/docs/api/java/sql/
package-summary.html
• List of Available JDBC Drivers
– http://developers.sun.com/product/jdbc/drivers
• Or, just look in your database vendor’s documentation
8

JDBC Drivers
• JDBC consists of two parts:
– JDBC API, a purely
Java-based API
– JDBC Driver Manager which
Java Application
JDBC API
– JDBC Driver Manager,which
communicates with
vendor-specific drivers that
f th l i ti
JDBC Driver Manager
JDBC Driver API
perform the real communication
with the database.
• Point: translation to vendor
Vendor Specific
JDBC Driver
JDBC-ODBC
Bridge
format is performed on
the client
– No changes needed
t
Vendor Specific
ODBC Driver
Database
to server
– Driver (translator) needed
on client
9
Database
JDBC Data Types
JDBC Type Java TypeJDBC Type Java Type
BIT boolean
TINYINT byte
SMALLINT short
INTEGER intINTEGER int
BIGINT long
REAL float
FLOAT double
DOUBLE
JDBC Type Java Type
NUMERIC BigDecimal
DECIMAL
DATE java sql DateDOUBLE
BINARY byte[]
VARBINARY
LONGVARBINARY
CHAR String
DATE java.sql.Date
TIME java.sql.Timestamp
TIMESTAMP
CLOB Clob
BLOB Blob
VARCHAR
LONGVARCHAR
BLOB Blob
ARRAY Array
DISTINCT mapping of underlying type
STRUCT Struct
REF Ref
10
REF Ref
JAVA_OBJECT underlying Java class

© 2010 Marty Hall
Steps for Using JDBC
JDBC Design Strategies
• In general, plan for changes to data access
– Limit the data access to single area of code
• Don’t distribute JDBC calls throughout the code
• Plan ahead for changing from JDBC to Hibernate orPlan ahead for changing from JDBC to Hibernate or
another tool
– Don’t return JDBC-specific (or Hibernate-specific)
objects from the data access layerobjects from the data-access layer
• Return ordinary Java objects instead
• In JDBC, plan for changes, p g
– Limit the definition of driver, URL, etc. to single location
• Let database experts do their stuff
– If database is complex, let database expert design the
database and design the queries
12

Seven Basic Steps in
Using JDBCUsing JDBC
1. Load the driver
– Not required in Java 6, so Java 6 needs only 6 steps.
2. Define the Connection URL
3 E t bli h th C ti3. Establish the Connection
4. Create a Statement object
5 E t5. Execute a query
6. Process the results
7 Cl th ti7. Close the connection
13
JDBC Step 1: Load the Driver
• Not required in Java 6
– In Java SE 6.0 and later (JDBC 4.0 and later), the driver
is loaded automatically.
• Java 5 and earlier• Java 5 and earlier
– Load the driver class only. The class has a static
initialization block that makes an instance and registers itg
with the DriverManager.
try {
Class.forName("com.mysql.jdbc.Driver");
Class.forName("oracle.jdbc.driver.OracleDriver");
} catch (ClassNotFoundException cnfe) {
System.out.println("Error loading driver: " cnfe);
}
14

JDBC Step 2: Define the
Connection URLConnection URL
• Remote databases
F t i “jdb d N ”– Format is “jdbc:vendorName:…”
• Address contains hostname, port, and database name
• Exact details given by supplier of JDBC driver
• Embedded Derby database• Embedded Derby database
– The “Java DB” (i.e., Apache Derby) is bundled with Java 6
and can be used for a database embedded in the same Java VM
that runs the app serverthat runs the app server.
– Format is “jdbc:derby:databaseName”
• Examples
String host = "dbhost.yourcompany.com";
String dbName = "someName";
int port = 1234;
String mySqlUrl = "jdbc:mysql//" + host + ":" + port +g y q j y q p
"/" + dbName;
String embeddedDerbyUrl = "jdbc:derby" + dbName;
15
JDBC Step 3: Establish the
ConnectionConnection
• Get the main connection
Properties userInfo = new Properties();
userInfo.put("user", "jay_debesee");
userInfo.put("password", "secret");
Connection connection =
DriverManager.getConnection(mySqlUrl, userInfo);
• Optionally, look up info about the databasep y, p
DatabaseMetaData dbMetaData =
connection.getMetaData();
String productName =g p
dbMetaData.getDatabaseProductName();
System.out.println("Database: " + productName);
String productVersion =g p
dbMetaData.getDatabaseProductVersion();
System.out.println("Version: " + productVersion);
16

JDBC Step 4: Make a Statement
• Idea
– A Statement is used to send queries or commands
• Statement types
S P dS C ll bl S– Statement, PreparedStatement, CallableStatement
• Details on other types given later
• ExampleExample
Statement statement =
connection.createStatement();
17
JDBC Step 5: Execute a Query
• Idea
– statement.executeQuery("SELECT … FROM …");
• This version returns a ResultSet
– statement executeUpdate("UPDATE ");– statement.executeUpdate( UPDATE … );
– statement.executeUpdate("INSERT …");
– statement.executeUpdate("DELETE…");
– statement.execute("CREATE TABLE…");
– statement.execute("DROP TABLE …");
E l• Example
String query =
"SELECT col1, col2, col3 FROM sometable";
ResultSet resultSet =
statement.executeQuery(query);
18

JDBC Step 6: Process the
ResultResult
• Important ResultSet methods
– resultSet.next()
• Goes to the next row. Returns false if no next row.
– resultSet getString("columnName")– resultSet.getString( columnName )
• Returns value of column with designated name in current
row, as a String. Also getInt, getDouble, getBlob, etc.
ltS t tSt i ( l I d )– resultSet.getString(columnIndex)
• Returns value of designated column. First index is 1 (ala
SQL), not 0 (ala Java).
– resultSet.beforeFirst()
• Moves cursor before first row, as it was initially. Also first
– resultSet absolute(rowNum)resultSet.absolute(rowNum)
• Moves cursor to given row (starting with 1). Also last and
afterLast.
19
JDBC Step 6: Process the
ResultResult
• Assumption
– Query was “SELECT first, last, address FROM…”
• Using column names
while(resultSet next()) {while(resultSet.next()) {
System.out.printf(
"First name: %s, last name: %s, address: %s%n",
resultSet.getString("first"),
resultSet.getString("last"),
resultSet.getString("address"));
}
U i l i di• Using column indices
while(resultSet.next()) {
System.out.printf(
"First name: %s last name: %s address: %s%n""First name: %s, last name: %s, address: %s%n",
resultSet.getString(1),
resultSet.getString(2),
resultSet.getString(3)); }20

JDBC Step 7: Close the
ConnectionConnection
• Idea
– When totally done, close the database connection.
However, opening a new connection is typically much
more expensive than sending queries on existingmore expensive than sending queries on existing
connections, so postpone this step as long as possible.
– Many JDBC drivers do automatic connection pooling
h l li i i l ili i– There are also many explicit connection pool utilities
• Example
connection close();connection.close();
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© 2010 Marty Hall
Using Apache Derby

Apache Derby: Overview
• Overview
– Written in Java. Good for small/medium applications
(less than gigabyte database size, few queries/second)
– Bundled with Java 6 but latest version can be– Bundled with Java 6, but latest version can be
downloaded from Apache for Java 1.4 and later.
• Embedded mode
– Database runs in same VM as Java app. Does not accept
network connections.
Perfect for Web apps– Perfect for Web apps
• Incredibly easy to set up. Just drop in one JAR file
• Good if database is accessed only from the Web apps
• Standalone mode
– Runs in separate VM. Accepts network connections.23
Downloading and Installing
DerbyDerby
• Downloading and documentation
http://db apache org/derby/– http://db.apache.org/derby/
• Use in embedded mode
– Code
F W b d d b j i WEB INF/lib• For Web apps, drop derby.jar in WEB-INF/lib
• For other apps, put derby.jar in CLASSPATH
– URL
• jdbc:derby:databaseNamejdbc:derby:databaseName
– Driver class name
• org.apache.derby.jdbc.EmbeddedDriver
• Not needed in Java 6!
– Username/password
• Any are legal since DB runs inside the application.
• Use in standalone mode
– See http://db.apache.org/derby/papers/DerbyTut/
– Consider MySQL, Oracle, etc. as alternatives
24

Setup Summary
• Setup summary
l d d l b f db h /d b /– Downloaded latest Derby ZIP from db.apache.org/derby/
• db-derby-10.5.3.0-bin.zip, but any recent version is fine
• You can also use version bundled with JDK 1.6.x
– Unzipped
– Put install_dir/lib/derby.jar into CLASSPATH
• Many options in Eclipse but if you make a Dynamic Web• Many options in Eclipse, but if you make a Dynamic Web
Project, drop derby.jar in WebContent/WEB-INF/lib
– That’s it (for embedded usage)!
C thi 90 d t i t lli O l• Compare this 90 second process to installing Oracle
• Creating database
– Can be created directly from Java using SQL commandsCan be created directly from Java using SQL commands
via JDBC. See later slides. Need to run creator code at
least once before accessing database.
25
Setup Details: Desktop Apps
• Putting derby.jar in
CLASSPATHCLASSPATH
– R-click on project in Eclipse, create
new folder called “lib”. Put derby.jar
in libin lib.
– R-click on project. Properties  Java
Build Path  Libraries  Add JARs
N i t t j t/lib/ d l t– Navigate to project/lib/ and select
derby.jar. Press OK.
– Manually run database creation code.
See “Prepared Statements” section for
code, but this needs to be done once
l I t l h tonly. In most real apps, you have to
query database, but someone else
creates the database.26

Setup Details: Web Apps
• Putting derby.jar in CLASSPATH
– Copy derby.jar to WEB-INF/lib
R d b i d S “P d S ”– Run database creation code. See “Prepared Statements”
section for code . This needs to be done once only, so best
way is to do it automatically in ServletContextListener. Iny y
most real apps, you have to query database, but someone
else creates the database.
• Reminder: full code can be downloaded fromReminder: full code can be downloaded from
http://courses.coreservlets.com/Course-Materials/
msajsp.html, so you can get db creation code there.
27
© 2010 Marty Hall
Using JDBC fromUsing JDBC from
Desktop Javap

Approach
• Same basic steps
– Load the driver
– Define the Connection URL
– Establish the ConnectionEstablish the Connection
– Create a Statement object
– Execute a query
– Process the results
– Close the connection
• Differences from JDBC in Web apps• Differences from JDBC in Web apps
– Results are often put into Swing or AWT interfaces
– If you use value in calculation, use getInt, getDouble, etc.y , g , g ,
– If value is only used for display in GUI, you can use
getString even if value is another type
29
Sample Database
• Table name
– employees
• Column names
id (int) The employee ID– id (int). The employee ID.
– firstname (varchar/String). Employee’s given name.
– lastname (varchar/String). Employee’s family name.
– position (varchar/String). Corporate position (eg, “ceo”).
– salary (int). Yearly base salary.
• Database name• Database name
– myDatabase
• Note
– See “Prepared Statements” section for code that created DB
30

Example:
Printing Employee InfoPrinting Employee Info
package coreservlets; The URL and the driver are the only parts that are specific to Derby. So, if you switch to MySql,
Oracle, etc., you have to change those two lines (or just one line in Java 6 with JDBC 4 driver,
since the driver no longer needs to be declared in that situation). The rest of the code is
import java.sql.*;
import java.util.*;
database independent.
public class ShowEmployees {
public static void main(String[] args) {
St i l "jdb d b D t b "String url = "jdbc:derby:myDatabase";
userInfo.put("user", "someuser");
( )userInfo.put("password", "somepassword");
String driver =
"org.apache.derby.jdbc.EmbeddedDriver";
showSalaries(url, userInfo, driver);
}
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Example: Printing Employee
Info (Connecting to Database)Info (Connecting to Database)
public static void showSalaries(String url,
Properties userInfo,Properties userInfo,
String driverClass) {
try {
// Load the driver. NOT NEEDED in Java 6!
// Class.forName(driverClass);
// Establish network connection to database.
Connection connection =Connection connection =
DriverManager.getConnection(url, userInfo);
System.out.println("Employeesn==========");
// Create a statement for executing queries.
Statement statement = connection.createStatement();
String query =
"SELECT * FROM employees ORDER BY salary";
// S d t d t b d t lt// Send query to database and store results.
ResultSet resultSet = statement.executeQuery(query);
32

Info (Processing Results)Info (Processing Results)
int id = resultSet.getInt("id");int id resultSet.getInt( id );
String firstName = resultSet.getString("firstname");
String lastName = resultSet.getString("lastname");
String position = resultSet.getString("position");
int salary = resultSet.getInt("salary");
System.out.printf
("%s %s (%s, id=%s) earns $%,d per year.%n",
firstName lastName position id salary);firstName, lastName, position, id, salary);
}
connection.close();
} catch(Exception e) {
System.err.println("Error with connection: " + e);
}
33
Info (Output)Info (Output)
Employees
==========
Gary Grunt (Gofer, id=12) earns $7,777 per year.
Gabby Grunt (Gofer, id=13) earns $8,888 per year.
Cathy Coder (Peon, id=11) earns $18,944 per year.
Cody Coder (Peon, id=10) earns $19,842 per year.
Danielle Developer (Peon, id=9) earns $21,333 per year.
David Developer (Peon, id=8) earns $21,555 per year.
Joe Hacker (Peon, id=6) earns $23,456 per year.
Jane Hacker (Peon, id=7) earns $32,654 per year.
Keith Block (VP, id=4) earns $1,234,567 per year.
Thomas Kurian (VP id=5) earns $2 431 765 per yearThomas Kurian (VP, id=5) earns $2,431,765 per year.
Charles Phillips (President, id=2) earns $23,456,789 per year.
Safra Catz (President, id=3) earns $32,654,987 per year.
Larry Ellison (CEO, id=1) earns $1,234,567,890 per year.y ( , ) $ , , , p y
34

© 2010 Marty Hall
Using JDBC fromUsing JDBC from
Web Appspp
Approach
• Same basic steps
L d h d i– Load the driver
– Define the Connection URL
– Establish the Connection
– Create a Statement object
– Execute a query
Process the results– Process the results
– Close the connection
• Differences from JDBC in desktop appsp pp
– Results are often put into HTML
– If value is inserted directly into HTML, you can use
getString even if value is another typegetString even if value is another type
– To support concurrent access, you usually use a driver
that supports connection pooling
36

Sample Database
• Table name
– employees
• Column names
id (int) The employee ID– id (int). The employee ID.
– firstname (varchar/String). Employee’s given name.
– lastname (varchar/String). Employee’s family name.
– position (varchar/String). Corporate position (eg, “ceo”).
– salary (int). Yearly base salary.
• Database name• Database name
– myDatabase
• Note
– See “Prepared Statements” section for code that created DB
37
A Servlet to Show Employee
InfoInfo
• Overview
– Same sample database as before
• DB type: Derby in embedded mode
• DB name: employeesDB name: employees
• Columns: id, firstname, lastname, position, salary
• Goal
– Build HTML table that shows all employees
• Approach
B ild HTML t bl di tl i l t– Build HTML table directly in servlet
• MVC combined with JSTL or custom tags might work
better, but this lecture does not assume familiarity with
th t ithose topics
• Basic JDBC code is the same either way
38

Employee Info Servlet
public class EmployeeServlet1 extends HttpServlet {
//private final String driver//private final String driver =
// "org.apache.derby.jdbc.EmbeddedDriver";
protected final String url = "jdbc:derby:myDatabase";
protected final String tableName = "employees";
protected final String username = "someuser";
protected final String password = "somepassword";
The URL and the driver are the only parts that are specific to Derby. So, if you switch to MySql,
39
since the driver no longer needs to be declared in that situation). The rest of the code is
database independent.
(Continued)(Continued)
public void doGet(HttpServletRequest request,
HttpServletResponse response)p p p )
throws ServletException, IOException {
response.setContentType("text/html");
PrintWriter out = response.getWriter();
String docType =
"<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 " +
"Transitional//EN"n";
String title = "Company Employees";St g t t e Co pa y p oyees ;
out.print(docType +
"<HTML>n" +
"<HEAD><TITLE>" + title + "</TITLE></HEAD>n" +
/ / "<LINK REL='STYLESHEET' HREF='./css/styles.css'n" +
" TYPE='text/css'>" +
"<BODY><CENTER>n" +
"<TABLE CLASS='TITLE' BORDER='5'>" +<TABLE CLASS TITLE BORDER 5 > +
" <TR><TH>" + title + "</TABLE><P>");
showTable(out);
out.println("</CENTER></BODY></HTML>"); }40

protected void showTable(PrintWriter out) {
try {try {
Connection connection = getConnection();
String query = "SELECT * FROM " + tableName;String query = "SELECT * FROM " + tableName;
ResultSet resultSet = statement.executeQuery(query);
printTableTop(connection, resultSet, out);
i tT bl B d ( ltS t t)printTableBody(resultSet, out);
connection.close();
} catch(Exception e) {
S t i tl ("E " )System.err.println("Error: " + e);
}
}
41
protected Connection getConnection()
throws Exception {throws Exception {
// Load database driver if it's not already loaded.
// Not needed in JDBC 4 (Java SE 6). Uncomment
// for earlier versions// for earlier versions.
// Class.forName(driver);
// E t bli h t k ti t d t b// Establish network connection to database.
userInfo.put("user", username);
I f t(" d" d)userInfo.put("password", password);
DriverManager.getConnection(url, userInfo);
return(connection);
}
42

protected void printTableTop(Connection connection,
ResultSet resultSetResultSet resultSet,
PrintWriter out)
throws SQLException {
out.println("<TABLE BORDER='1'>");out.println( <TABLE BORDER 1 > );
// Print headings from explicit heading names
String[] headingNames =
{ "ID", "First Name", "Last Name",{ , , ,
"Position", "Salary" };
out.print("<TR>");
for (String headingName : headingNames) {g g g
out.printf("<TH>%s", headingName);
}
out.println();
}
43
protected void printTableBody(ResultSet resultSet,
PrintWriter out)PrintWriter out)
throws SQLException {
// Step through each row in the result set and print cells
out.println("<TR ALIGN='RIGHT'>");
out.printf(" <TD>%d", resultSet.getInt("id"));
out.printf(" <TD>%s", resultSet.getString("firstname"));
out.printf(" <TD>%s", resultSet.getString("lastname"));
out.printf(" <TD>%s", resultSet.getString("position"));
out.printf(" <TD>$%,d%n", resultSet.getInt("salary"));
}}
out.println("</TABLE>");
}
}}
44

Employee Info Servlet (Results)
45
© 2010 Marty Hall
Using MetaData

Using MetaData
• Idea
– For most queries, you know column names and database
version ahead of time. But you can discover this
dynamically as well.dynamically as well.
• System-wide data
– connection.getMetaData().getDatabaseProductName()g () g ()
– connection.getMetaData().getDatabaseProductVersion()
• Table-specific data
– resultSet.getMetaData().getColumnCount()
• When using the result, remember that
the index starts at 1, not 0
– resultSet.getMetaData().getColumnName()
47
Using MetaData: Example
public class EmployeeServlet2 extends EmployeeServlet1 {
protected void printTableTop(Connection connectionprotected void printTableTop(Connection connection,
ResultSet resultSet,
PrintWriter out)
throws SQLException {throws SQLException {
// Look up info about the database as a whole.
DatabaseMetaData dbMetaData = connection.getMetaData();
String productName =g p
dbMetaData.getDatabaseProductName();
String productVersion =
dbMetaData.getDatabaseProductVersion();g
out.println("<UL>n" +
" <LI><B>Database:</B>n" + productName +
" <LI><B>Version:</B>n" + productVersion +
"</UL>");
48

Using MetaData: Example
out.println("<TABLE BORDER='1'>");
// Discover and print headings// Discover and print headings
ResultSetMetaData resultSetMetaData =
resultSet.getMetaData();
int columnCount = resultSetMetaData.getColumnCount();
out.println("<TR>");
// Column index starts at 1 (a la SQL), not 0 (a la Java).
for(int i=1; i <= columnCount; i++) {
out.printf("<TH>%s", resultSetMetaData.getColumnName(i));
}
out.println();
}}
}
49
Using MetaData: Results
50

© 2010 Marty Hall
Using PreparedUsing Prepared
Statements
(Parameterized Commands)
Overview
• Situation
– You are repeatedly executing query or update where
format stays consistent, but values change
– You can make a parameterized query or update then pass– You can make a parameterized query or update, then pass
in values for the placeholders
• Advantagesg
– More convenient than string concatenation
– Significantly faster with most drivers and databases
If h l i d h l ibl– If the values contain user data, much less susceptible to
SQL injection attacks
52

Steps
• Make a placeholder
A T bl h l (i d S i )– Assume someTable has two columns (int and String)
String template =
"INSERT INTO someTable VALUES(?, ?)";
P dSt t t i tPreparedStatement inserter =
connection.prepareStatement(template);
• Substitute in values
– Use setInt(index), setString(index), etc. Remember
indices start with 1, not 0.
for(…) {o ( ) {
inserter.setInt(1, someInt);
inserter.setString(2, someString)
}}
• Execute command
• inserter.executeUpdate();
53
Creating the Database
• Roles
– Most JDBC developers do not need to create the database
– That is the job of the database system admin
Apache Derby• Apache Derby
– You can run Derby-specific scripts and create the
database interactivelyy
– Or, you can use Java and JDBC
• Using PreparedStatement simplifies the process
Si l “ D t b ” l• Simple “myDatabase” example
– Created with Java and JDBC
Triggered from a ServletContextListener so database– Triggered from a ServletContextListener so database
creation code is executed at least once
54

Creating Sample Database
public class EmbeddedDbCreator {
// Driver class not needed in JDBC 4 0 (Java SE 6)// Driver class not needed in JDBC 4.0 (Java SE 6)
// private String driver =
// "org.apache.derby.jdbc.EmbeddedDriver";
private String protocol = "jdbc:derby:";p g p j y
private String username = "someuser";
private String password = "somepassword";
private String dbName = "myDatabase";
private String tableName = "employees";
private Properties userInfo;
bli E b dd dDbC t () {public EmbeddedDbCreator() {
userInfo = new Properties();
userInfo.put("user", username);
userInfo put("password" password);userInfo.put( password , password);
}
55
public void createDatabase() {
Employee[] employees = {Employee[] employees {
new Employee(1, "Larry", "Ellison", "CEO",
1234567890),
new Employee(2, "Charles", "Phillips", "President",p y ( , , p , ,
23456789),
new Employee(3, "Safra", "Catz", "President",
32654987),
…
};
56

try {
String dbUrl = protocol + dbName + ";create=true";String dbUrl protocol + dbName + ;create true ;
DriverManager.getConnection(dbUrl, userInfo);
String format = "VARCHAR(20)";
String tableDescription =
String.format
("CREATE TABLE %s" +( CREATE TABLE %s +
"(id INT, firstname %s, lastname %s, " +
"position %s, salary INT)",
tableName, format, format, format);
statement.execute(tableDescription);
57
String template =
String.format("INSERT INTO %s VALUES(?, ?, ?, ?, ?)",String.format( INSERT INTO %s VALUES(?, ?, ?, ?, ?) ,
tableName);
PreparedStatement inserter =
connection.prepareStatement(template);
for(Employee e: employees) {
inserter.setInt(1, e.getEmployeeID());
inserter.setString(2, e.getFirstName());
inserter setString(3 e getLastName());inserter.setString(3, e.getLastName());
inserter.setString(4, e.getPosition());
inserter.setInt(5, e.getSalary());
inserter.executeUpdate();
System.out.printf("Inserted %s %s.%n",
e.getFirstName(),
e.getLastName());
}}
inserter.close();
connection.close();
58

Triggering Database Creation
• Database needs to be created once
– Not for every request
– Not even for every time server restarts
Goal• Goal
– Create table when Web app is loaded
• try/catch block in creation code halts process if tabletry/catch block in creation code halts process if table
already exists
• Possible approaches
S l i h i d i i i d b l i h– Servlet with creation code in init, and web.xml with
<load-on-startup>1</load-on-startup>
– ServletContextListenerServletContextListener
• Same effect as above, but more straightforward
– For desktop apps, just manually run the code once.59
Triggering Database Creation:
ListenerListener
package coreservlets;
import javax.servlet.*;
public class DatabaseInitializer
implements ServletContextListener {
public void contextInitialized(ServletContextEvent event) {
new EmbeddedDbCreator().createDatabase();
}}
public void contextDestroyed(ServletContextEvent event) {}
}
60

Triggering Database Creation:
web xmlweb.xml
…
<listener><listener>
<listener-class>
coreservlets.DatabaseInitializer
</listener-class>
</listener>
61
© 2010 Marty Hall
Advanced Features

Transactions
• Idea
– By default, after each SQL statement is executed the
changes are automatically committed to the database
– Turn auto-commit off to group two or more statements– Turn auto-commit off to group two or more statements
together into a transaction
ti tA t C it(f l )connection.setAutoCommit(false);
– Call commit to permanently record the changes to the
database after executing a group of statements
– Call rollback if an error occurs
63
Transactions: Example
DriverManager.getConnection(url, userProperties);g g ( , p );
connection.setAutoCommit(false);
try {
statement.executeUpdate(...);
statement executeUpdate( );statement.executeUpdate(...);
...
connection.commit();
} catch (Exception e) {
try {
connection.rollback();
} catch (SQLException sqle) {
// report problem// report problem
}
} finally {
try {
ti l ()connection.close();
} catch (SQLException sqle) { }
}
64

Useful Connection Methods
(for Transactions)(for Transactions)
• getAutoCommit/setAutoCommit
– By default, a connection is set to auto-commit
– Retrieves or sets the auto-commit mode
commit• commit
– Force all changes since the last call to commit to become
permanentp
– Any database locks currently held by this Connection
object are released
llb k• rollback
– Drops all changes since the previous call to commit
Releases any database locks held by this Connection– Releases any database locks held by this Connection
object
65
Using JNDI and DataSource
• Idea
– Use abstract name to get connection from a data source
• Advantages
L h d i h h i d– Lets you change data source without changing code
– Available in multiple Web apps for network databases
(not embedded Derby!)( y )
• Disadvantage
– Requires server-specific registration of data source
• Code for steps 1-3 replaced by:
Context context = new InitialContext();
DataSource dataSource = (DataSource)context lookupDataSource dataSource = (DataSource)context.lookup
("java:comp/env/jdbc/dbName");
Connection connection = dataSource.getConnection();
66

DataSource: Tomcat Configuration
(META-INF/context xml)(META-INF/context.xml)
<?xml version="1.0" encoding="UTF-8"?>
<Context><Context>
<Resource
name="jdbc/myDatabase"
driverClassName="org apache derby jdbc ClientDriver"driverClassName="org.apache.derby.jdbc.ClientDriver"
url="jdbc:derby:myDatabase"
type="javax.sql.DataSource"
" "username="someuser"
password="somepassword"
auth="Container"
A ti "8" /maxActive="8" />
</Context>
67
More JDBC Options
• Stored procedures
• Changing buffer size
• Connection poolingp g
• Hibernate/JPA and other ORM tools
– See tutorials at coreservlets.com
• JSP Standard Tag Library (JSTL)
– Custom tags to hide JDBC details.g
• Some developers use JSTL to loop down the ResultSet.
Disadvantage: ties presentation layer to JDBC.
• Some developers use JSTL to actually do queries Simple• Some developers use JSTL to actually do queries. Simple.
Disadvantage: very inflexible and violates MVC principle.
68

© 2010 Marty Hall
Wrap-Up
JDBC and Derby References
• Books
JDBC API T i l d R f b M d Fi h– JDBC API Tutorial and Reference by Maydene Fisher,
Jon Ellis, and Jonathan Bruce (Prentice Hall)
– Expert Oracle JDBC Programming by R.M. Menon
(APress)
– JDBC Recipes: A Problem-Solution Approach by
Mahmoud Parsian (APress)( )
• Sun JDBC tutorial
– http://java.sun.com/docs/books/tutorial/jdbc/
Derb references• Derby references
– Derby beginner’s tutorial
• http://db.apache.org/derby/papers/DerbyTut/g y y
– Derby 10.4 manuals
• http://db.apache.org/derby/manuals/index.html#docs_10.4
70

Summary
1. Load the driver
N t i d i J 6 Cl f N th i– Not required in Java 6; use Class.forName otherwise
2. Define the Connection URL
– jdbc:vendor:blah (vendor gives exact format)
3. Establish the Connection
– DriverManager.getConnection
4 Create a Statement object4. Create a Statement object
– connection.createStatement
5. Execute a query
– statement.executeQuery
6. Process the results
– Loop using resultSet.next()Loop using resultSet.next()
– Call getString, getInt, etc.
7. Close the connection
71
© 2010 Marty Hall
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10 jdbc

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