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Programming in Java
JDBC/ODBC
Java DataBase Access
蔡文能
交通大學資訊工程學系
[email protected]
交通大學資訊工程學系
Java
JDBC
Agenda
Extend your JDK and JRE
Introduction to ODBC and JDBC
JDBC Drivers
JDBC Statements
 Statement
 PreparedStatement
 CallableStatement
ResultSet
Transactions concept
CORBA again
交通大學資訊工程學系 蔡文能
第2頁
Java
JDBC
Extend your JDK and JRE
把 所有 class 都壓縮到一個 .jar 檔案 (名稱隨意, 但不要與現有的重複)
例如:
jar cvf myutilabc.jar M*.class So*.class
(也可用 WINZIP 壓成 ZIP 檔再 rename 成 .jar 檔)
把壓好的 .jar 檔 copy 到 你 JDK 根目錄下的 \jre\lib\ext\ 即可




注意 .jar 檔中的目錄樹要與各 class 宣告的 package 相符合
就是說不可以欺騙 Java compiler 與 Interpreter (JVM)
可用 jar tvf your.jar 看看 (或用 WINZIP 看)
打 jar 看看 help
這樣 javac MyClass.java 編譯 或 java MyClass 執行就都不用指定classpath
 若不是放 JDK 的 \jre\lib\ext\ 中, 則要指定 .jar 檔為你的 classpath
javac -classpath ./mydir/myutil.jar; MyTest.java
java -classpath ./mydir/myutil.jar; MyTest
(注意 分號不能省; 可以多個 jar 檔用 ; 分開, 也可為目錄)
交通大學資訊工程學系 蔡文能
第3頁
Java
JDBC
Internet Technology
RMI
JDBC
CORBA
java.net
TCP/IP
Network
交通大學資訊工程學系 蔡文能
Copyright © 1997 Alex Chaffee
第4頁
Java
JDBC
Access to the DataBase
Most popular form of database system is the Relational
DataBase System. (invented by Dr. E.F.Codd)
Examples: Oracle, Sybase, IBM DB2, MS Sequel Server, MS
Access. (Informix 已在2001年被 IBM 併購)
Structured Query Language (SQL) is used among relational
databases to construct queries.
These queries can be stand-alone or embedded within
applications. This form of SQL is known as embedded SQL.
2001年7月2日，IBM公司順利完成斥資10億美元對Informix公司的資料庫
資產的收購。 IBM公司因此成為世界最大的中介軟體(MiddleWare)供應商 。
交通大學資訊工程學系 蔡文能
第5頁
Java
JDBC
Relational Databases
關聯式資料庫
Invented by Dr. E.F.Codd.
data stored in records which live in tables
Multiple tables.
Each table is associated with a list of fields.
Each field (column) has a name, and type.
Each table is made up of a number of records (rows).
Each row contains the values for each field.
“Relation” (as in “Relational”) means row to column (not
table to table) 列對欄位的關係; 注意不是表格對表格 !
交通大學資訊工程學系 蔡文能
第6頁
Java
JDBC
Open DataBase Connectivity
(ODBC) Standard
ODBC (Open Database Connectivity) is a Microsoft standard from the
mid 1990’s.
ODBC standard is an interface by which application programs can access
and process SQL databases in a DBMS-independent manner. It contains:
 A Data Source that is the database, its associated DBMS, operating system
and network platform
 A DBMS Driver that is supplied by the DBMS vendor or independent
software companies
 A Driver Manager that is supplied by the vendor of the O/S platform where
the application is running. (例如MicroSoft提供Windows的)
It requires an ODBC driver to be provided for each database system from which
you want to manipulate data.
交通大學資訊工程學系 蔡文能
第7頁
Java
JDBC
ODBC Application Architecture
Application
Class1
Class2
ODBC
Driver Manager
DriverType1
DataSource1
交通大學資訊工程學系 蔡文能
DriverType2
DriverType3
DataSource2
DataSource3
第8頁
Java
JDBC
Java Support for ODBC : JDBC
When applications written in Java want to access data
sources, they use classes and associated methods provided
by Java DBC (JDBC) API.
JDBC is specified an an “interface”.
An interface in Java can have many “implementations”.
So it provides a convenient way to realize many “drivers”
JDBC is implemented via classes in the java.sql package
交通大學資訊工程學系 蔡文能
第9頁
Java
JDBC
Java Support for embedded SQL
Java supports embedded SQL.
Also it provides an JDBC API as a standard way
to connect to common relational databases.
You need a JDBC:ODBC bridge for using the
embedded SQL in Java.
 Other JDBC Drivers are available for some RDBMS
java.sql package and an extensive exception
hierarchy.
交通大學資訊工程學系 蔡文能
第10頁
Java
JDBC
SQL
SQL was initiated by IBM as part of its System R research
prototype in the late 1970s
There are many different types of SQL commands (SELECT,
INSERT, UPDATE, DELETE, …).
For example: to create a new record:
"INSERT INTO password (Name, Password) VALUES ('Dave', 'blah')"
Reference:
A guide to SQL standard –
4th Edition. CJ Date & Hugh Darman. Addison Wesley. 1997.
http://www.opengroup.org/public/tech/datam/sql.htm
交通大學資訊工程學系 蔡文能
第11頁
Java
JDBC
General SELECT statement
SELECT column1, column2, ..., columnN
FROM table1 [, table2, ..., tableN ]
[WHERE clause]
column# are the field names.
table# are table names.
The WHERE clause can restrict the rows used to
determine the result.
交通大學資訊工程學系 蔡文能
第12頁
Java
JDBC
Some other SQL Statements
INSERT INTO table ( field1, field2 )
VALUES ( value1, value2 )
 inserts a new record into the named table
UPDATE table SET ( field1 = value1, field2
= value2 ) WHERE condition
 changes an existing record or records
DELETE FROM table WHERE condition
 removes all records that match condition
交通大學資訊工程學系 蔡文能
Copyright © 1997 Alex Chaffee
第13頁
Java
JDBC
Embedded SQL
Direct SQL (= ad-hoc SQL) is rarely used
 Also know as interactive SQL (iSQL)
In practice: SQL is embedded in some application
code
 user interaction, devices, programming logic
SQL code is enbedded using special syntax into a
host language (C, Java, etc.)
交通大學資訊工程學系 蔡文能
第14頁
Java
JDBC
JDBC
JDBC
Java
DataBase
Connectivity
交通大學資訊工程學系 蔡文能
第15頁
Java
JDBC
Side View of a Distributed Application
Client
E.g. a
Java Applet
Middle
Ware
Middle
Ware
IDL
Server
E.g. DBMS
IDL
Network
Internet (TCP/IP)
IDL = Interface Definition Language
交通大學資訊工程學系 蔡文能
第16頁
Java
JDBC
JDBC Components
Driver Manager: Loads database drivers, and manages the
connection between application & driver.
Driver: Translates API calls to operations for a specific data
source.
Connection: A session between an application and a driver.
Statement: A SQL statement to perform a query or an update
operation.
Metadata: Information about the returned data, driver and the
database.
Result Set : Logical set of columns and rows returned by
executing a statement.
交通大學資訊工程學系 蔡文能
第17頁
Java
JDBC
JDBC Classes (java.sql.*)
Java supports DB facilities by providing classes and interfaces
for its components
DriverManager class
Connection interface (abstract class)
Statement interface (to be instantiated with values from the
actual SQL statement)
ResultSet interface
 ResultSet = the records returned from a SQL Statement
JDBC is implemented via classes in the java.sql package
交通大學資訊工程學系 蔡文能
第18頁
Java
交通大學資訊工程學系 蔡文能
JDBC
第19頁
Java
JDBC
JDBC Class Diagram
交通大學資訊工程學系 蔡文能
Copyright © 1997 Alex Chaffee
第20頁
Java
JDBC
Running a JDBC Application
Phase
Initialisation
Processing
Termination
交通大學資訊工程學系 蔡文能
Task
Relevant java.sql classes
Load driver
Create connection
DriverManager
Connection
Generate SQL statements
Process result data
Statement
ResultSet etc.
Terminate connection
Release data structures
Connection
Statement etc.
第21頁
Java
JDBC
JDBC PseudoCode
All JDBC programs do the following:
 1) load the JDBC driver
 2) Specify the name and location of the database being used
 3) Connect to the database with a Connection object
 4) Execute a SQL query using a Statement object
 5) Get the results in a ResultSet object
 6) Finish by closing the ResultSet, Statement and
Connection objects
交通大學資訊工程學系 蔡文能
Continued
第22頁
Java
JDBC
JDBC Application Architecture
Application
Connection
Statement
ResultSet
Driver Manager
Driver
DataSource
交通大學資訊工程學系 蔡文能
Driver
Driver
DataSource
DataSource
第23頁
Java
JDBC
A Simple JDBC application
loadDriver
getConnection
createStatement
execute(SQL)
Result handling
yes
More
results ?
no
closeStatment
closeConnection
import java.sql.*;
public class jdbctest {
public static void main(String args[]){
try{
Class.forName("org.postgresql.Driver");
Connection con = DriverManager.getConnection
("jdbc:postgresql://lsir-cis-pc8:5401/pcmdb", "user", "passwd");
Statement stmt = con.createStatement();
ResultSet rs = stmt.executeQuery
("select name, number from pcmtable where number < 2");
while(rs.next())
System.out.println(rs.getString(1) + " (" + rs.getInt(2) + ")");
stmt.close()
con.close();
} catch(Exception e) {
System.err.println(e);
}}}
交通大學資訊工程學系 蔡文能
第24頁
Java
JDBC
Driver Manager Class
Provides static, “factory” methods for creating objects
implementing the connection interface.
 Factory methods create objects on demand
when a connection is needed to a DB driver,
DriverManager does it using its factory methods. E.g.:
Connection foo = DriverManager.getConnection(DBURL);
java.sql.Connection interface corresponds to a
session (a connection with a specific database).
交通大學資訊工程學系 蔡文能
第25頁
Java
JDBC
JDBC Drivers
JDBC-ODBC Bridge.
2) A native API partly Java Technology enabled driver.
3) A net protocol driver (through Middleware).
4) A fully Java Technology enabled driver direct built into
DB engine.
Type I
ODBC
ODBC
“Bridge”
Driver
Type II
CLI (.lib)
“Native”
JDBC
Type III
Middleware
“Middleware”
Server
Type IV
“Pure”
1)
交通大學資訊工程學系 蔡文能
第26頁
Java
JDBC
Type I Drivers
Use bridging technology
Requires installation/configuration on client
machines
Not good for Web / Applet
e.g. ODBC Bridge
 sun.jdbc.odbc.JdbcOdbcDriver
交通大學資訊工程學系 蔡文能
Copyright © 1997 Alex Chaffee
第27頁
Java
JDBC
Type II Drivers
Native API drivers
Requires installation/configuration on client
machines
Used to leverage existing CLI libraries
Usually not thread-safe
Mostly obsolete now
e.g. Intersolv Oracle Driver, WebLogic drivers
交通大學資訊工程學系 蔡文能
Copyright © 1997 Alex Chaffee
第28頁
Java
JDBC
Type III Drivers
Calls middleware server, usually on database host
Very flexible -- allows access to multiple
databases using one driver
Only need to download one driver
But it’s another server application to install and
maintain
e.g. Symantec DBAnywhere
交通大學資訊工程學系 蔡文能
Copyright © 1997 Alex Chaffee
第29頁
Java
JDBC
Type IV Drivers
100% Pure Java -- the Holy Grail
Use Java networking libraries to talk directly to
database engines
Only disadvantage: need to download a new
driver for each database engine
e.g. Oracle, mSQL
交通大學資訊工程學系 蔡文能
Copyright © 1997 Alex Chaffee
第30頁
Java
JDBC
Where to get JDBC Drivers
There are a number of JDBC drivers
available. (more than 200 )
Information on installing them is available
at :
http://industry.java.sun.com/products/jdbc/drivers
http://developers.sun.com/product/jdbc/drivers/
交通大學資訊工程學系 蔡文能
第31頁
Java
交通大學資訊工程學系 蔡文能
JDBC
第32頁
Java
JDBC
Using JDBC Drivers
Loading a driver
 Class.forName(“sun.jdbc.odbc.JdbcOdbcDriver” );
 OR
DriverManager.registerDriver(new sun.jdbc.odbc.JdbcOdbcDriver( ) );
Making a Connection
String url = “jdbc:oracle:oci8:@mydb”;
Connection con = DriverManager.getConnection(url, “mylogin”, “password”);
url identifies the Data Source in Database.
See next Slide.
交通大學資訊工程學系 蔡文能
第33頁
Java
JDBC
Implicit Driver Loading
Setting system property: jdbc.drivers
 A colon-separated list of driver classnames.
Can be set when starting the application
java -Djdbc.drivers=org.postgresql.Driver application
Can also be set from within the Java application
Properties prp = System.getProperties();
prp.put("jdbc.drivers"
"com.mimer.jdbc.Driver:org.postgresql.Driver");
System.setProperties(prp);
The DriverManager class attempts to load all the classes
specified in jdbc.drivers when the DriverManager class is
initialized.
交通大學資訊工程學系 蔡文能
第34頁
Java
JDBC
JDBC Database URL (1/2)
Format:
jdbc:subprotocol:source
each driver has its own subprotocol
each subprotocol has its own syntax for the source
jdbc:odbc:DataSource
 e.g. jdbc:odbc:NCTUDB
jdbc:msql://host[:port]/database
 e.g. jdbc:msql://foo.nctu.edu.tw:3388/sampledb
交通大學資訊工程學系 蔡文能
Copyright © 1997 Alex Chaffee
第35頁
Java
JDBC
JDBC Database URL (2/2)
jdbc:odbc: //host.domain.com: 2048 /data/file
The comms
protocol
The machine
holding the
database.
The port
used for the
connection.
The path to
the database
on the machine
e.g. jdbc:odbc:nctuDB
交通大學資訊工程學系 蔡文能
第36頁
Java
JDBC
Another Example using IBM DB2
url identifies the Data Source in Database.
See previous Slide.
// register the driver with DriverManager
Class.forName("COM.ibm.db2.jdbc.app.DB2Driver");
String url = "jdbc:db2:DATABASE_NAME";
Connection con =DriverManager.getConnection(url,
"USERNAME", "PASSWORD");
交通大學資訊工程學系 蔡文能
第37頁
Java
JDBC
JDBC Statements
A JDBC statement object is used to send your
SQL statement to the database server
A JDBC statement is associated with an open
connection and not any single SQL statement
JDBC provides three classes of SQL statement
 Statement
 PreparedStatement
 CallableStatement
交通大學資訊工程學系 蔡文能
第38頁
Java
JDBC
JDBC Programming Steps
Import necessary packages; Ex: import java.sql.*;
Load JDBC driver(driver should have been installed)
Data source and its location should have been registered.
Allocate Connection object, Statement object and
ResultSet object
Execute query using Statement object
Retrieve data from ResultSet object
Close Connection object.
交通大學資訊工程學系 蔡文能
第39頁
Java
JDBC
Obtaining JDBC drivers
Usually provided (free) by DataBase vendors
Common ones
 oracle.jdbc.driver.OracleDriver
 com.mysql.jdbc.Driver
 sun.jdbc.odbc.JdbcOdbcDriver
Need to download and install
 In a webapp, put the Jar file in WEB-INF/lib
交通大學資訊工程學系 蔡文能
第40頁
Java
JDBC
Connecting to a Database
Via a DriverManager (old)
 Class.forName(DriverClassName).newInstance();
 Connection con =
DriverManager.getConnection(URL,Username,Password);
Via a DataSource (new)
 Create DataSource object in configuration (e.g. in
Tomcat’s context.xml file)
交通大學資訊工程學系 蔡文能
第41頁
Java
JDBC
Creating JDBC Statement
// con is a Connection to a DB
Statement stmt = con.createStatement();
String createINTROCS = “Create table INTROCS “+
“(SSN Integer not null, Name VARCHAR(32), “+ “Marks
Integer)”;
stmt.executeUpdate(createINTROCS);
String insertMYCS = “Insert into INTROCS values “+
“(123456789, abc, 100)”;
stmt.executeUpdate(insertMYCS);
交通大學資訊工程學系 蔡文能
第42頁
Java
JDBC
ResultSet
A ResultSet is returned when you execute an SQL
statement:
// stmt is a Statement created via creatStatement( )
ResultSet rs =
stmt.executeQuery("SELECT * FROM
password");
A ResultSet object is similar to a ‘table’ of answers,
which can be examined by moving a ‘pointer’ (cursor).
ResultSet can be used to store the query result
交通大學資訊工程學系 蔡文能
第43頁
Java
JDBC
Processing the ResultSet
ResultSet can be used to store the query result
The ResultSet class contains many methods for accessing
the value of a column of the current row
 can use the column name or position
 e.g. get the value in the lastName column:
rs.getString("lastName")
The ‘tricky’ aspect is that the values are SQL data, and so
must be converted to Java types/objects.
There are many methods for accessing/converting the data,
e.g.
 getString(), getDate(), getInt(), getFloat(),
getObject()
交通大學資訊工程學系 蔡文能
第44頁
Java
JDBC
Impedance Mismatch
Example: SQL in Java:
 Java uses int, char[..], objects, etc
 SQL uses tables
Impedance mismatch = incompatible types
Why not use only one language?
 SQL cannot do everything that the host language can do
Solution: use cursors
交通大學資訊工程學系 蔡文能
第45頁
Java
JDBC
Moving the
DataBase Cursor
cursor
23
5
John
Mark
17
98
Paul
Peter
Cursor operations:
 first(), last(), next(), previous(), etc.
Typical code:
String queryINTROCS = “select * from INTROCS”;
ResultSet rs = Stmt.executeQuery(queryINTROCS);
While (rs.next( )) {
int ssn = rs.getInt(“SSN”);
String name = rs.getString(“NAME”);
int marks = rs.getInt(“MARKS”);
}
交通大學資訊工程學系 蔡文能
Note: column number
can also be used in
place of column
name.
Refer to
java.sql.ResulSet
API for more details
第46頁
Java
JDBC
More on DataBase Cursors
Cursors can also modify a relation
rset.updateString("script", "ebay");
rset.updateRow( ); // updates the row in the data source
The cursor can be a scrolling one: can go forward,
backward
first(), last(), next(), previous(), absolute(5)
We can determine the order in which the cursor
will get tuples by the ORDER BY clause in the
SQL query
交通大學資訊工程學系 蔡文能
第47頁
Java
JDBC
isNull
In SQL, NULL means the field is empty
Not the same as 0 or "" (空字串)
In JDBC, you must explicitly ask if a field is null
by calling ResultSet.isNull(column_name)
交通大學資訊工程學系 蔡文能
Copyright © 1997 Alex Chaffee
第48頁
Java
JDBC
Dynamic JDBC Statements
Variables within SQL statement
Precompiled once, multiple executions
PreparedStatement for invocation
PreparedStatement stmt = con.prepareStatement (
"SELECT * FROM data WHERE date = ?");
stmt.setDate (1, j_date);
ResultSet rset = stmt.executeQuery();
交通大學資訊工程學系 蔡文能
第49頁
Java
JDBC
Prepared Statement (1/2)
Unlike “Statement,” it is given a SQL statement when it is
created.
Used when you want to execute “Statement” object many
times
E.g
String insert = “Insert into INTROCS (?,?,?)”;
PreparedStatement stmt2 = con.prepareStatement(insert);
//…
stmt2.setInt(1,123456789);
stmt2.setString(2, “abc”);
stmt2.setInt(3,100);
stmt2.executeUpdate( );
交通大學資訊工程學系 蔡文能
第50頁
Java
JDBC
Prepared Statement (2/2)
Executing Select Statement
E.g
String query =“SELECT Name from INTROCS where SSN=?”;
PreparedStatement stmt2 = con.prepareStatement(query);
stmt2.setInt(1, mySSN);
ResultSet rs = stmt2.executeQuery( );
While (rs.next( ) )
System.out.println(rs.getString(Name);
You may extract individual columns, rows or cell
from the ResultSet using the metadata.
交通大學資訊工程學系 蔡文能
第51頁
Java
JDBC
Callable Statement
Used for executing stored procedures
Example
String createProcedure = “Create Procedure ShowGoodStudents” + “as Select
Name from INTROCS where Marks >= 90)”;
Stmt.executeUpdate(createProcedure);
CallableStatement cs = con.prepareCall(“(call ShowGoodStudents)”);
ResultSet rs = cs.executeQuery( );
交通大學資訊工程學系 蔡文能
第52頁
Java
JDBC
ResultSet Meta Data (1/3)
Meta data is the information about the database
Stores the number, types and properties of
ResultSet’s columns.
// rs is a ResultSet
ResultSetMetaData rsm = rs.getMetaData();
int number = rsm.getColumnCount();
for (int i=0; i< number;i++)
System.out.println(rsm.getColumnName(i));
You may extract individual columns, rows or cell
from the ResultSet using the metadata.
交通大學資訊工程學系 蔡文能
第53頁
Java
JDBC
ResultSet Meta Data (2/3)
Meta data example
ID
007
008
Name
James Bond
Aj. Andrew
交通大學資訊工程學系 蔡文能
Course
Shooting
Kung Fu
Mark
meta data
99
1
第54頁
Java
JDBC
ResultSet Meta Data (3/3)
What's the number of columns in the ResultSet?
What's a column's name?
What's a column's SQL type?
What's the column's normal max width in chars?
What's the suggested column title for use in printouts and displays?
What's a column's number of decimal digits?
Does a column's case matter?
Is the column a cash value?
Will a write on the column definitely succeed?
Can you put a NULL in this column?
Is a column definitely not writable?
Can the column be used in a where clause?
Is the column a signed number?
Is it possible for a write on the column to succeed?
…, and so on...
交通大學資訊工程學系 蔡文能
Copyright © 1997 Alex Chaffee
第55頁
Java
JDBC
DatabaseMetaData
// con is a Connection
DatabaseMetaData dbm = con.getMetaData();
What tables are available?
What's our user name as known to the database?
Is the database in read-only mode?
If table correlation names are supported, are they restricted
to be different from the names of the tables?
and so on…
交通大學資訊工程學系 蔡文能
Copyright © 1997 Alex Chaffee
第56頁
Java
JDBC
Using Meta Data
// rs is a ResultSet
ResultSetMetaData md = rs.getMetaData();
int numCols = md.getColumnCount();
for (int i = 0; i <= numCols; i++) {
if (md.getColumnType(i) ==
Types.CHAR)
System.out.println(
md.getColumnName(i) )
}
交通大學資訊工程學系 蔡文能
第57頁
Java
JDBC
More Meta Data Methods
getTableName()
getPrecision()
 number of decimal digits in the column
isSigned()
 returns true if column has signed numbers
isCurrency()
etc.
交通大學資訊工程學系 蔡文能
第58頁
Java
JDBC
Another Example of using Meta Data
ResultSet rset = stmt.executeQuery(“SELECT * FROM data”);
ResultSetMetaData rsmeta = rset.getMetaData();
int numCols = rsmeta.getColumnCount();
for (int i=1; i<=numCols; i++) {
int ct
= rsmeta.getColumnType(i);
String cn = rsmeta.getColumnName(i);
String ctn = rsmeta.getColumnTypeName(i);
System.out.println(“Column #” + i + “: “ + cn +
“ of type “ + ctn + “ (JDBC type: “ + ct + “)”);
}
交通大學資訊工程學系 蔡文能
第59頁
Java
JDBC
Matching Java and SQL Data Types
SQL Type
BIT
CHAR
VARCHAR
DOUBLE
FLOAT
INTEGER
REAL
DATE
TIME
TIMESTAMP
Java class
Boolean
String
String
Double
Double
Integer
Double
java.sql.Date
java.sql.Time
java.sql.TimeStamp
交通大學資訊工程學系 蔡文能
ResultSet get method
getBoolean()
getString()
getString()
getDouble()
getDouble()
getInt()
getFloat()
getDate()
getTime()
getTimestamp()
第60頁
Java
JDBC
Example: simpJDBC.java (1/4)
// simpJDBC.java
// Displays the firstnames and lastnames
// of the Authors table in the Books db.
import java.sql.*;
public class simpJDBC {
public static void main(String[] args)
{
// The URL for the Books database.
// ’Protected' by a login and password.
String url = "jdbc:odbc:Books";
String username = "anonymous";
String password = "guest";
:
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第61頁
Java
JDBC
Example: simpJDBC.java (2/4)
try {
// load the JDBC-ODBC Bridge driver
Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
// connect to db using DriverManager
Connection conn =
DriverManager.getConnection( url,
username, password );
// Create a statement object
Statement statement = conn.createStatement();
// Execute the SQL query
ResultSet rs = statement.executeQuery(
"SELECT lastName, firstName FROM Authors" );
:
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第62頁
Java
JDBC
Example: simpJDBC.java (3/4)
// Print the result set
while( rs.next() )
System.out.println(
rs.getString("lastName") + ", " +
rs.getString("firstName") );
// Close down
statement.close();
conn.close();
}
:
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第63頁
Java
JDBC
Example: simpJDBC.java (4/4)
catch ( ClassNotFoundException cnfex ) {
System.err.println(
"Failed to load JDBC/ODBC driver." );
cnfex.printStackTrace();
System.exit( 1 ); // terminate program
}
catch ( SQLException sqlex ) {
System.err.println( sqlex );
sqlex.printStackTrace();
}
} // end of main()
} // end of simpJDBC class
交通大學資訊工程學系 蔡文能
第64頁
Java
JDBC
Output of simpJDBC.java
交通大學資訊工程學系 蔡文能
第65頁
Java
JDBC
Transactions concept
Transaction = more than one statement which
must all succeed (or all fail) together
If one fails, the system must reverse all previous
actions
Also can’t leave DB in inconsistent state halfway
through a transaction
COMMIT = complete transaction
ROLLBACK = abort
交通大學資訊工程學系 蔡文能
Copyright © 1997 Alex Chaffee
第66頁
Java
JDBC
Transactions and JDBC (1/2)
JDBC allows SQL statements to be grouped together
into a single transaction
Transaction control is performed by the Connection object, default
mode is auto-commit, I.e., each sql statement is treated as a transaction
We can turn off the auto-commit mode with
con.setAutoCommit(false);
And turn it back on with con.setAutoCommit(true);
Once auto-commit is off, no SQL statement will be committed until an
explicit is invoked con.commit( );
At this point all changes done by the SQL statements will be made
permanent in the database.
交通大學資訊工程學系 蔡文能
第67頁
Java
JDBC
Transactions and JDBC (2/2)
If we don’t want certain changes to be made permanent, we can issue
con.rollback();
Any changes made since the last commit will be ignored – usually
rollback is used in combination with Java’s exception handling ability to
recover from unpredictable errors.
Example: // con is a Connection
con.setAutocommit(false);
Statement stmt = con.createStatement( );
stmt.executeUpdate(“INSERT INTO INTROCS VALUES
(1234,’John’,0)”);
con.rollback( );
stmt.executeUpdate(“INSERT INTO INTROCS VALUES
(1234,’John’,0)”);
con.commit( );
con.setAutoCommit(true);
交通大學資訊工程學系 蔡文能
第68頁
Java
JDBC
Error Handling
Each SQL statement can generate errors
 Thus each SQL method should be put into a try-block
Exceptions are reported through exceptions of
class SQLException
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第69頁
Java
JDBC
Handling Errors with Exceptions
Programs should recover and leave the database in a consistent state.
In Java statements which are expected to “throw” an exception or a
warning are enclosed in a try block.
If a statement in the try block throws an exception or warning, it can be
caught in one of the corresponding catch statements
Example: // stmt is a statement
try{
stmt.executeUpdate(queryINTROCS);
} catch (SQLException e){
System.out.println(e.getMessage( ))
}
交通大學資訊工程學系 蔡文能
第70頁
Java
JDBC
Java Example using JDBC (1/3)
import java.sql.*;
import oracle.jdbc.driver.*;
import oracle.sql.*;
import java.math.BigDecimal;
import java.util.Map;
import java.io.*;
class employee
{
public static void main (String args [])
throws SQLException, IOException {
String user, pass, snum, namer;
int enumber;
user = readEntry("userid : ");
pass = readEntry("password: ");
// Connect
DriverManager.registerDriver(new
oracle.jdbc.driver.OracleDriver ());
OracleConnection conn = (OracleConnection)
DriverManager.getConnection("jdbc:oracle:oci8:@ccdb",
user,pass);
交通大學資訊工程學系 蔡文能
第71頁
Java
JDBC
Java Example using JDBC (2/3)
Statement stmt = conn.createStatement ();
ResultSet rset = stmt.executeQuery
("select distinct eno,ename,zip,hdate from employees");
while (rset.next ()) {
namer = rset.getString(2);
if ( !rset.wasNull() ) {
System.out.println(rset.getInt(1) + " " +
namer
+ " " +
rset.getInt(3) + " " +
rset.getDate(4));
}
}
System.out.println();
conn.close();
}
交通大學資訊工程學系 蔡文能
第72頁
Java
JDBC
Java Example using JDBC (3/3)
//readEntry function -- to read input string
static String readEntry(String prompt) {
try {
StringBuffer buffer = new StringBuffer();
System.out.print(prompt);
System.out.flush();
int c = System.in.read();
while(c != '\n' && c != -1) {
buffer.append((char)c);
c = System.in.read();
}
return buffer.toString().trim();
} catch (IOException e) {
return "";
}
}
}
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第73頁
Java
JDBC
More ResultSet Methods (1/4)
boolean next()
 activates the next row
 the first call to next() activates the first row
 returns false if there are no more rows
void close()
 disposes of the ResultSet
 allows you to re-use the Statement that created it
 automatically called by most Statement methods
交通大學資訊工程學系 蔡文能
Copyright © 1997 Alex Chaffee
第74頁
Java
JDBC
More ResultSet Methods (2/4)
Type getType(int columnIndex)
 returns the given field as the given type
 fields indexed starting at 1 (not 0)
Type getType(String columnName)
 same, but uses name of field
 less efficient
int findColumn(String columnName)
 looks up column index given column name
交通大學資訊工程學系 蔡文能
Copyright © 1997 Alex Chaffee
第75頁
Java
JDBC
More ResultSet Methods (3/4)
String getString(int columnIndex)
boolean getBoolean(int columnIndex)
byte getByte(int columnIndex)
short getShort(int columnIndex)
int getInt(int columnIndex)
long getLong(int columnIndex)
float getFloat(int columnIndex)
double getDouble(int columnIndex)
Date getDate(int columnIndex)
Time getTime(int columnIndex)
Timestamp getTimestamp(int columnIndex)
交通大學資訊工程學系 蔡文能
Copyright © 1997 Alex Chaffee
第76頁
Java
JDBC
More ResultSet Methods (4/4)
String getString(String columnName)
boolean getBoolean(String columnName)
byte getByte(String columnName)
short getShort(String columnName)
int getInt(String columnName)
long getLong(String columnName)
float getFloat(String columnName)
double getDouble(String columnName)
Date getDate(String columnName)
Time getTime(String columnName)
Timestamp getTimestamp(String columnName)
交通大學資訊工程學系 蔡文能
Copyright © 1997 Alex Chaffee
第77頁
Java
JDBC
JDBC Reference
Reference:
http://java.sun.com/products/jdbc/
http://developer.java.sun.com/developer/onlineTraining/
Database/JDBC20Intro/
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第78頁
Java
JDBC
http://java.sun.com/products/jdbc/
交通大學資訊工程學系 蔡文能
第79頁
Java
JDBC
More than RMI
CORBA
 Common Object Request Broker Architecture
 http://www.corba.org/
OMG
 http://www.omg.org/
J2EE (Sun)
 J2EE Tutorial:
http://java.sun.com/j2ee/1.4/docs/tutorial/doc/
ASP.Net (Microsoft)
交通大學資訊工程學系 蔡文能
第80頁
Java
JDBC
What is CORBA?
Common Object Request Broker Architecture
Defines a family of open software interface specifications for
distributed object computing.
http://www.omg.org
Inside every Java Runtime Environment.
Commonly used in middle tier and backend (e.g. database)
connections.
Open Source and Commercial Implementations Available
Usually buried deep inside the software
 Difficult or impossible to tell when it is being used
交通大學資訊工程學系 蔡文能
第81頁
Java
JDBC
What is Distributed Object Computing?
Extends the benefits of object-oriented technology
across process and machine boundaries to
encompass entire networks.
Attempts to make remote objects appear to
programmers as if they were local objects in the
same process. This is called location
transparency.
交通大學資訊工程學系 蔡文能
第82頁
Java
JDBC
CORBA Independence
Open Standard for Distributed Object Oriented
Design
Independent of Hardware Platform
Independent of Operating System
Independent of Programming Language
Independent of Object Location
http://www.omg.org
OMG = Object Management Group
Consortium of 800+ companies founded in 1989.
交通大學資訊工程學系 蔡文能
第83頁
Java
JDBC
Object Request Broker (ORB) 1/2
ORBs mediate between objects and things that use them
(clients)
IDL
Client
Object
IDL
Object Request Broker
IDL = Interface Definition Language
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第84頁
Java
JDBC
Object Request Broker (ORB) 2/2
The glue that binds parts
together is the ORB
The Interface to an object
can be distributed over a
network
Shape of boundary
is defined in IDL
IDL = Interface Definition Language
交通大學資訊工程學系 蔡文能
第85頁
Java
JDBC
ORBs: Medium for Integration
C
C++
Perl
Delphi
ORB
Ada
Java
ORB
CORBA / IIOP—Internet Inter-ORB Protocol
ORB
Application
交通大學資訊工程學系 蔡文能
ActiveX
第86頁
Java
JDBC
IIOP—Internet Inter-ORB Protocol
IIOP
 The Internet Inter-ORB Protocol, defined in
the Spec as a vendor-independent, wire-level
network protocol on top of TCP/IP. This allows
ORB implementations of different vendors to
interoperate.
交通大學資訊工程學系 蔡文能
第87頁
Java
JDBC
JDBC: Use DBMS in Java
謝謝捧場
http://www.csie.nctu.edu.tw/~tsaiwn/java/
蔡文能
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第88頁