Transaction isolation levels in JDBC control how one transaction can see changes made by other transactions running at the same time. They help prevent problems such as dirty reads, non-repeatable reads, and phantom reads. The isolation level is set using the setTransactionIsolation() method of the Connection interface. JDBC provides four standard isolation levels: TRANSACTION_READ_UNCOMMITTED, TRANSACTION_READ_COMMITTED, TRANSACTION_REPEATABLE_READ, and TRANSACTION_SERIALIZABLE. A higher isolation level provides stronger data consistency but may reduce concurrency and performance.
JDBC Transaction Isolation Levels
| Isolation Level | Description |
|---|---|
TRANSACTION_READ_UNCOMMITTED |
Allows a transaction to read uncommitted changes made by another transaction. It provides the lowest isolation. |
TRANSACTION_READ_COMMITTED |
Allows a transaction to read only committed data. It prevents dirty reads. |
TRANSACTION_REPEATABLE_READ |
Ensures that data already read by a transaction cannot be changed by another transaction until the first transaction completes. |
TRANSACTION_SERIALIZABLE |
Provides the highest isolation and prevents dirty reads, non-repeatable reads, and phantom reads. |
Program : Applying All Four Isolation Levels to Transactions
This program demonstrates how the four transaction isolation levels can be applied to database transactions. For each level, an employee record is retrieved and the transaction is committed after the operation is completed.
import java.sql.*;
public class FourIsolationLevelsExample {
public static void main(String[] args) {
String url = "jdbc:mysql://localhost:3306/jdbc_demo";
String username = "root";
String password = "password";
String sql =
"SELECT employee_id, employee_name, salary " +
"FROM employee " +
"WHERE employee_id = 101";
try {
Connection con =
DriverManager.getConnection(
url, username, password);
con.setAutoCommit(false);
// 1. READ_UNCOMMITTED
performTransaction(
con,
Connection.TRANSACTION_READ_UNCOMMITTED,
sql);
// 2. READ_COMMITTED
performTransaction(
con,
Connection.TRANSACTION_READ_COMMITTED,
sql);
// 3. REPEATABLE_READ
performTransaction(
con,
Connection.TRANSACTION_REPEATABLE_READ,
sql);
// 4. SERIALIZABLE
performTransaction(
con,
Connection.TRANSACTION_SERIALIZABLE,
sql);
con.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
static void performTransaction(
Connection con,
int isolationLevel,
String sql) throws SQLException {
con.setTransactionIsolation(isolationLevel);
System.out.println(
"\nTransaction Isolation Level: " +
getIsolationName(isolationLevel));
Statement stmt = con.createStatement();
ResultSet rs = stmt.executeQuery(sql);
if (rs.next()) {
System.out.println(
"Employee ID: " +
rs.getInt("employee_id"));
System.out.println(
"Employee Name: " +
rs.getString("employee_name"));
System.out.println(
"Salary: " +
rs.getDouble("salary"));
}
con.commit();
System.out.println(
"Transaction committed.");
rs.close();
stmt.close();
}
static String getIsolationName(int level) {
switch (level) {
case Connection.TRANSACTION_READ_UNCOMMITTED:
return "READ_UNCOMMITTED";
case Connection.TRANSACTION_READ_COMMITTED:
return "READ_COMMITTED";
case Connection.TRANSACTION_REPEATABLE_READ:
return "REPEATABLE_READ";
case Connection.TRANSACTION_SERIALIZABLE:
return "SERIALIZABLE";
default:
return "UNKNOWN";
}
}
}Execution and Output:
PS D:\test> javac -classpath ".;D:\test\mysql-connector.jar" FourIsolationLevelsExample.java
PS D:\test> java -classpath ".;D:\test\mysql-connector.jar" FourIsolationLevelsExample
Transaction Isolation Level: READ_UNCOMMITTED
Employee ID: 101
Employee Name: Ravi
Salary: 78500.0
Transaction committed.
Transaction Isolation Level: READ_COMMITTED
Employee ID: 101
Employee Name: Ravi
Salary: 78500.0
Transaction committed.
Transaction Isolation Level: REPEATABLE_READ
Employee ID: 101
Employee Name: Ravi
Salary: 78500.0
Transaction committed.
Transaction Isolation Level: SERIALIZABLE
Employee ID: 101
Employee Name: Ravi
Salary: 78500.0
Transaction committed.Code language: CSS (css)