JDBC and Hibernate
Joshua Scotton
Connecting to Relational DBs
try {
Class.forName("com.mysql.jdbc.Driver");
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
try {
Connection con =
DriverManager.getConnection(url, user, pass);
con.close();
} catch (SQLException e) {
e.printStackTrace();
}
stmt = con.createStatement();
stmt.executeUpdate(sqlString);
stmt.close();
stmt.executeQuery(sqlString);
Class.forName("com.mysql.jdbc.Driver");
Connection con =
DriverManager.getConnection(url, user, pass);
Statement stmt = con.createStatement();
ResultSet rs = stmt.executeQuery(sqlString);
while (rs.next()) {
System.out.println(rs.getString("username"));
}
stmt.close();
con.close();
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next() - moves the cursor forward one row. Returns true if
the cursor is now positioned on a row and false if the cursor
is positioned after the last row.
previous() - moves the cursor backwards one row. Returns
true if the cursor is now positioned on a row and false if the
cursor is positioned before the first row.
first() - moves the cursor to the first row in the ResultSet
object. Returns true if the cursor is now positioned on the
first row and false if the ResultSet object does not contain
any rows.
last() - moves the cursor to the last row in the ResultSet
object. Returns true if the cursor is now positioned on the
last
row
and
false
if
the
ResultSet
object
does not contain any rows.
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/register?action=new-user
◦ New user entry form
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/register?action=register
◦ Saves new user to database
String sql1="insert into user (username,
password) values
('"+username+"','"+password+"')";
String sql2="insert into role (username, role)
values ('"+username+"','user')";
Class.forName("com.mysql.jdbc.Driver");
Connection con =
DriverManager.getConnection(url, user, pass);
Statement stmt = con.createStatement();
stmt.executeUpdate(sql1);
stmt.executeUpdate(sql2);
stmt.close();
con.close();
Hacking the Registration Form
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Username: “Josh”
"insert into role (username, role) values
('"+username+"','user')“
SQL: insert into role (username, role) values
(‘Josh','user')
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Username: “Josh’,’admin’) -- “
"insert into role (username, role) values
('"+username+"','user')“
SQL: insert into role (username, role) values
(‘Josh',’admin’) -- 'user')
sql="insert into user (username,
password) values (?,?)”;
PreparedStatement pstmt =
con.prepareStatement(sql);
pstmt.setString(1, username);
pstmt.setString(2, password);
pstmt.executeUpdate();
try {
con.setAutoCommit(false);
PreparedStatement pstmt = con.prepareStatement(sql1);
pstmt.setString(1, username);
pstmt.setString(2, password);
pstmt.executeUpdate();
pstmt = con.prepareStatement(sql2);
pstmt.setString(1, username);
pstmt.executeUpdate();
con.commit();
} catch ( SQLException e ) {
con.rollback();
}
Database Abstraction Layer
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Download jar from
http://www.hibernate.org/downloads
Create
Create
Create
Create
the Java Objects
Mapping Files
the Hibernate Configuration File
a Session management class
<hibernate-mapping>
<class name="TestBean" table="Test">
<id name="id" column="test_id">
<generator class="increment"/>
</id>
<property name="title" column="test_title"/>
<property name="description"
column="test_description"/>
</class>
</hibernate-mapping>
In TestBean:
<set name="questions" cascade="save-update"
inverse="true" table="TestQuestion">
<key>
<column name="test_id" not-null="true" />
</key>
<one-to-many class="TestQuestion" />
</set>
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In TestQuestionBean:
<many-to-one name="test" class="Test”>
<column name="test_id" not-null="true" />
</many-to-one>
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This defines the database configuration
Hibernate will work with many different
database types including:
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MySQL
HSQL DB
Oracle
MS SQL Server
<session-factory>
<property name="connection.driver_class">
com.mysql.jdbc.Driver</property>
<property name="connection.url">
jdbc:mysql://localhost:3306/quizmaster</property>
<property name="connection.username">username</property>
<property name="connection.password">password</property>
<property name="dialect">
org.hibernate.dialect.MySQLDialect</property>
<property name="show_sql">true</property>
<property name="current_session_context_class">thread</property>
<property name="hibernate.hbm2ddl.auto">create</property>
<mapping
resource="webdev/quizmaster/HibernateMapping.hbm.xml" />
</session-factory>
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Not mandatory but used in most cases
Handles session creation
Session session =
HibernateUtil.getCurrentSession();
session.beginTransaction();
TestBean tBean = new TestBean();
session.save(tBean);
session.getTransaction().commit();
Session session =
HibernateUtil.getSessionFactory().openSession();
Transaction trans = session.beginTransaction();
List<TestBean> tests =
session.createQuery("from Test as t order by
t.test_title asc").list();
trans.commit();
session.close();
You work with objects in your system (if your system
has been designed well). Even if using JDBC, you will
end up making some translation layer, so that you
transfer your data to your objects. Unless you are
extremely good Hibernate will be better at translation
than any custom-made solution.
 It doesn't deprive you of control. You can control
things in very small details, and if the API doesn't
have some remote feature - execute a native query
and you have it.
However:
 ORMs do add a small performance overhead, which in
some cases can't be ignored. It will depend on your
application and whether this overhead is significant
enough to outweigh the benefits of using an ORM.
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Stability - being around for so many years, it
lacks any major problems
dictates the standards in the ORM field
Documentation – There are many tutorials,
common problem solutions, etc
Powerful - you can translate a very complex
object model into a relational model.
Database Support - it has support for any
major and medium RDBMS
Connecting to the Database
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Added JavaBeans for Result, ResultAnswer
Added Hibernate mapping for all Beans
viewTest now allows the user to take the test
saveResult saves score
Added new view for listTests to index
Added new view for listResults to admin
Added TestManager