Copyright Oracle Corporation, 1998. All rights reserved. 6 Accessing a Database Using the JDBC API.

Copyright Oracle Corporation, 1998. All rights reserved.

66

Accessing a Database Using the JDBC API

Accessing a Database Using the JDBC API

Copyright Oracle Corporation, 1998. All rights reserved.6-6-22

ObjectivesObjectives

After completing this lesson, you should be able to do the following:

• Connect to a database using JDBC

• Perform queries using JDBC

• Invoke prepared statements and stored procedures

• Use transaction commit and rollback

• Use Oracle JDBC extensions

After completing this lesson, you should be able to do the following:

• Connect to a database using JDBC

• Perform queries using JDBC

• Invoke prepared statements and stored procedures

• Use transaction commit and rollback

• Use Oracle JDBC extensions


JDBC class library

OverviewOverview

Javasoft

driver

ODBC C library

Oracle

driver

OCI C library

Oracle

driver

Java sockets

JBCL components

Your Java code

ODBC-based OCI-based Pure Java


• JDBC is a standard Java class library, to query and modify relational data

– Import java.sql.* in your Java code

• JDBC is modeled after ODBC

– Supports SQL92 syntax and types

– Allows for vendor-specific extensions

– Many Oracle extensions

• JDBC is a standard Java class library, to query and modify relational data

– Import java.sql.* in your Java code

• JDBC is modeled after ODBC

– Supports SQL92 syntax and types

– Allows for vendor-specific extensions

– Many Oracle extensions

What Is JDBC?What Is JDBC?


Relationship Between JDBC Classes

Relationship Between JDBC Classes

ResultSet

ResultSetMetaData

DatabaseMetaData

Statement

Connection

DriverManager

1

6

4

2

35


Registering a JDBC DriverRegistering a JDBC Driver

• JDBC drivers must register themselves with the DriverManager

• Drivers register themselves automatically when they are loaded

• JDBC drivers must register themselves with the DriverManager

• Drivers register themselves automatically when they are loaded

try {

Class c = Class.forName(

"oracle.jdbc.driver.OracleDriver");

}

catch (ClassNotFoundException e) {

e.printStackTrace();

}


•DriverManager is used to open a connection to a database

• The database is specified using a URL, which identifies the JDBC driver

•jdbc:<protocol>:<connectString>

Example:

•DriverManager is used to open a connection to a database

• The database is specified using a URL, which identifies the JDBC driver

•jdbc:<protocol>:<connectString>

Example:

Connecting to a DatabaseConnecting to a Database

jdbc:oracle:thin:@<host>:<port>:<sid>


Example: Connecting to Oracle Example: Connecting to Oracle

The following code connects to an Oracle database

• Uses the Oracle JDBC Thin driver

The following code connects to an Oracle database

• Uses the Oracle JDBC Thin driver

Connection conn;

try { conn = DriverManager.getConnection( "jdbc:oracle:thin:@myhost:1521:orcl", "theUser", "thePassword");}catch (SQLException e) {…}


Obtaining Database Metadata Obtaining Database Metadata

Connection can be used to get a DatabaseMetaData object

• This provides many methods to obtain metadata for the database

Connection can be used to get a DatabaseMetaData object

• This provides many methods to obtain metadata for the database Connection conn; … try { DatabaseMetaData dm = conn.getMetaData(); String s1 = dm.getURL(); String s2 = dm.getSQLKeywords(); boolean b1 = dm.supportsTransactions(); boolean b2 = dm.supportsSelectForUpdate();}catch (SQLException e) {…}


Three interfaces are defined, providing the following capabilities:

• Execute queries and otherDML/DDL operations

• Execute precompiled statements

• Call stored procedures

Three interfaces are defined, providing the following capabilities:

• Execute queries and otherDML/DDL operations

• Execute precompiled statements

• Call stored procedures

StatementsStatements

Statement

PreparedStatement

CallableStatement


Statements and QueriesStatements and Queries

• The Statement class can be used as follows, to execute a query

•executeQuery() executes a SQL query, and returns a ResultSet

• The Statement class can be used as follows, to execute a query

•executeQuery() executes a SQL query, and returns a ResultSet

try { Statement stmt = conn.createStatement(); ResultSet rset = stmt.executeQuery ("select ENAME, SAL from EMP");}catch (SQLException e) {…}


Processing Query ResultsProcessing Query Results

•ResultSet holds a table of result data returned by a SQL query

• Support for cursors

– Cursor starts at beginning of data set

– Use next() to move to next record

• Retrieve data using getXXX() methods, mapping results to equivalent Java types

•ResultSet holds a table of result data returned by a SQL query

• Support for cursors

– Cursor starts at beginning of data set

– Use next() to move to next record

• Retrieve data using getXXX() methods, mapping results to equivalent Java types


Processing Results: ExampleProcessing Results: Example

try { ResultSet rset = stmt.executeQuery( "select ENAME, SAL from EMP");

while (rset.next()) { String ename = rset.getString(1); BigDecimal sal = rset.getBigDecimal(2, 2);

// Can also access columns by name: // String ename = rset.getString("ENAME"); // BigDecimal sal = rset.getBigDecimal("SAL");

}}catch (SQLException e) {…}


Obtaining ResultSet Metadata Obtaining ResultSet Metadata

ResultSet can be used to get a ResultSetMetaData object

• Provides result set metadata

ResultSet can be used to get a ResultSetMetaData object

• Provides result set metadata

try { ResultSet rset = … ; ResultSetMetaData md = rset.getMetaData();

while (rset.next()) { for (int i = 0; i < md.getColumnCount(); i++) { String lbl = md.getColumnLabel(); String typ = md.getColumnTypeName(); … }} catch (SQLException e) {…}


Mapping Database Types to Java Types

Mapping Database Types to Java Types

ResultSet maps database types to Java types

ResultSet maps database types to Java types

ResultSet rset = stmt.executeQuery ("select EMPNO, ENAME, HIREDATE from EMP");

BigDecimal empno = rset.getBigDecimal(1, 2);String ename = rset.getString(2); Date hiredate = rset.getDate(3);

Col Name

EMPNO

ENAME

HIREDATE

Type

NUMBER

VARCHAR2

DATE


Prepared StatementsPrepared Statements

If you need to execute a statement several times, with different bind variables:

• Use a PreparedStatement object

• Identify bind variables with a ? sign

If you need to execute a statement several times, with different bind variables:

• Use a PreparedStatement object

• Identify bind variables with a ? sign

try { Connection conn = DriverManager.getConnection(…);

PreparedStatement pstmt = conn.prepareStatement("update EMP set SAL = ?"); … } catch (SQLException e) {…}


Binding Variables and Executing a PreparedStatement

Binding Variables and Executing a PreparedStatement

Specify bind variables using the methods setXXX() in PreparedStatementSpecify bind variables using the methods setXXX() in PreparedStatement

try { PreparedStatement pstmt = conn.prepareStatement("update EMP set SAL = ?"); … pstmt.setBigDecimal(1, new BigDecimal(55000)); pstmt.executeUpdate();

pstmt.setBigDecimal(1, new BigDecimal(65000)); pstmt.executeUpdate(); … } catch (SQLException e) {…}


Stored ProceduresStored Procedures

To call a stored procedure, you need a CallableStatement object

•IN parameters are set using setXXX(), as for a PreparedStatement

• Return values and OUT parameters must be registered, to specify their types

To call a stored procedure, you need a CallableStatement object

•IN parameters are set using setXXX(), as for a PreparedStatement

• Return values and OUT parameters must be registered, to specify their types


Calling Stored ProceduresCalling Stored Procedures

getSal(v_ename in varchar2, v_job out varchar2)

return numeric …

CallableStatement cs =

conn.prepareCall( "{? = call getSal(?,?)}" );

cs.registerOutParameter(1, Types.NUMERIC);

cs.setString(2, "smith");

cs.registerOutParameter(3, Types.VARCHAR);

cs.executeUpdate();

System.out.println("Smith makes " + cs.getFloat(1) +

" as a " + cs.getString(3));


TransactionsTransactions

• Transactions are governed by the autoCommit property in Connection

– true initially, causing a separate transaction per SQL statement

• If you want to take control:

• Transactions are governed by the autoCommit property in Connection

– true initially, causing a separate transaction per SQL statement

• If you want to take control:

Connection conn = DriverManager.getConnection(…);

conn.setAutoCommit(false); // No autocommits now

… // Issue SQL statements

conn.commit(); … or … // Commit transaction

conn.rollback(); // Rollback transaction


PreparedStatement

CallableStatement

Oracle Extensions Oracle Extensions

Oracle provides many extensions to standard JDBC, for example:Oracle provides many extensions to standard JDBC, for example:

Connection

Statement

ResultSet

OraclePreparedStatement

OracleCallableStatement

OracleStatement

OracleResultSet

OracleConnection


Prefetching Rows in a QueryPrefetching Rows in a Query

• Oracle JDBC drivers enable you to set the number of rows to prefetch to the client

– Can be defined for the Connection

– Alternatively, define for individual Statements

• Reduces the number of round trips to the server

• Oracle JDBC drivers enable you to set the number of rows to prefetch to the client

– Can be defined for the Connection

– Alternatively, define for individual Statements

• Reduces the number of round trips to the server


Prefetching Rows: ExamplePrefetching Rows: Example

Connection conn = DriverManager.getConnection(…);

((OracleConnection)conn).setDefaultRowPrefetch(7);

Statement st = conn.createStatement();

ResultSet rs = st.executeQuery("select * from EMP");

while (rs.next())

System.out.println(rs.getString(1));

((OracleStatement)st).setRowPrefetch(2);

rs = st.executeQuery("select * from EMP");

while (rs.next())

System.out.println(rs.getString(1));


Prespecifying Column TypesPrespecifying Column Types

• When a query is performed, JDBC uses a network round trip to identify result types

• Oracle JDBC enables column types to be predefined

– Eliminates one network round trip

• When a query is performed, JDBC uses a network round trip to identify result types

• Oracle JDBC enables column types to be predefined

– Eliminates one network round trip

((OracleStatement)st).clearDefines();

((OracleStatement)st).defineColumnType(col, type);


Prespecifying Types: ExamplePrespecifying Types: Example

Statement st = conn.createStatement();

// Ask for the EMPNO column as a String.

// This avoids a round trip to get the column type.

// EMPNO is converted to a string on the server.

((OracleStatement)st).defineColumnType

(1, Types.VARCHAR);

ResultSet rs = st.executeQuery

("select EMPNO from EMP");

while (rs.next())

System.out.println (rs.getString(1));


Batched Updates of Prepared StatementsBatched Updates of Prepared Statements

• By default, prepared statements are executed as soon as executeUpdate() is called

• Oracle JDBC enables prepared statements to be batched:

• By default, prepared statements are executed as soon as executeUpdate() is called

• Oracle JDBC enables prepared statements to be batched:

((OraclePreparedStatement)ps).setExecuteBatch(3);

((OraclePreparedStatement)ps).executeBatch();

((OraclePreparedStatement)ps).getExecuteBatch();


Guided Practice: When Are the Statements Executed?

Guided Practice: When Are the Statements Executed?

OraclePreparedStatement methods

• setExecuteBatch() and sendBatch()

OraclePreparedStatement methods

• setExecuteBatch() and sendBatch()

PreparedStatement ps = conn.prepareStatement

("update EMP set SAL = SAL + 100");

((OraclePreparedStatement)ps).setExecuteBatch(3);

ps.executeUpdate();

ps.executeUpdate();

ps.executeUpdate();

ps.executeUpdate();

((OraclePreparedStatement)ps).sendBatch()


The ROWID Pseudo ColumnThe ROWID Pseudo Column

• Oracle JDBC drivers do not support getCursorName() for cursor usage

• Oracle provides a ROWID type instead

– ROWID is a pseudo column in a query

– Retrieve its value from a ResultSet, using getString()

• ROWID can also be bound to a parameter in a PreparedStatement

• Oracle JDBC drivers do not support getCursorName() for cursor usage

• Oracle provides a ROWID type instead

– ROWID is a pseudo column in a query

– Retrieve its value from a ResultSet, using getString()

• ROWID can also be bound to a parameter in a PreparedStatement


Example: Using ROWID for In-Place Updates

Example: Using ROWID for In-Place Updates

ResultSet rset = stmt.executeQuery

("select ENAME, ROWID from EMP for update");

PreparedStatement pstmt = conn.prepareStatement

("update EMP set ENAME = ? where ROWID = ?");

while (rset.next()) {

String ename = rset.getString(1);

String rowid = rset.getString(2);

pstmt.setString(1, ename.toLowerCase());

pstmt.setString(2, rowid);

pstmt.executeUpdate();

}


Oracle Extensions for Stored Subprograms

Oracle Extensions for Stored Subprograms

• Stored subprograms in standard JDBC:

• Oracle JDBC supports Oracle escape syntax, and PL/SQL anonymous blocks:

• Stored subprograms in standard JDBC:

• Oracle JDBC supports Oracle escape syntax, and PL/SQL anonymous blocks:

CallableStatement cs = conn.prepareCall

( "{? = call func(?,?)}" );

CallableStatement cs2 = conn.prepareCall

("begin :1 = func(:2,:3); end;");


Oracle CURSOR TypeOracle CURSOR Type

Oracle provides a CURSOR type, to iterate a result set returned by a stored procedureOracle provides a CURSOR type, to iterate a result set returned by a stored procedure

CallableStatement cs = conn.prepareCall

("begin open ? for select ENAME from EMP; end;");

cs.registerOutParameter(1, OracleTypes.CURSOR);

cs.executeUpdate();

ResultSet cursor =

((OracleCallableStatement)cs).getCursor(1);

while (cursor.next())

System.out.println(cursor.getString(1));


Suppressing Table RemarksSuppressing Table Remarks

•DatabaseMetaData TABLE_REMARKS should be avoided

• Require slow outer joins

• To enable or disable table remarks:

•DatabaseMetaData TABLE_REMARKS should be avoided

• Require slow outer joins

• To enable or disable table remarks:

((OracleConnection)conn).setRemarksReporting(bool);


SummarySummary

• JDBC provides classes and interfaces for database connectivity

– Connect to a database

– Perform DML and DDL operations

– Prepared statements and stored procedures

• Oracle JDBC provides many extensions

– Performance and flexibility

• JDBC provides classes and interfaces for database connectivity

– Connect to a database

– Perform DML and DDL operations

– Prepared statements and stored procedures

• Oracle JDBC provides many extensions

– Performance and flexibility


Practice 6-1 OverviewPractice 6-1 Overview

• Connect to a database, using JDBC

• Create and execute a query, using JDBC

• Iterate a result set

• Perform an update operation

• Perform an update operation with parameters

• Connect to a database, using JDBC

• Create and execute a query, using JDBC

• Iterate a result set

• Perform an update operation

• Perform an update operation with parameters

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Copyright Oracle Corporation, 1998. All rights reserved. 6 Accessing a Database Using the JDBC API.

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