Java Mysql 简明教程
Java & MySQL - Commit & Rollback
一旦完成更改,并且你希望提交更改,请按照如下方式调用连接对象的 commit() 方法:
conn.commit( );
否则,若要回滚对使用 conn 命名的 Connection 对数据库作出的更新,则使用以下代码:
conn.rollback( );
以下示例说明了如何使用提交和回滚对象 -
try{
//Assume a valid connection object conn
conn.setAutoCommit(false);
Statement stmt = conn.createStatement();
String SQL = "INSERT INTO Employees " +
"VALUES (106, 20, 'Rita', 'Tez')";
stmt.executeUpdate(SQL);
//Submit a malformed SQL statement that breaks
String SQL = "INSERTED IN Employees " +
"VALUES (107, 22, 'Sita', 'Singh')";
stmt.executeUpdate(SQL);
// If there is no error.
conn.commit();
}catch(SQLException se){
// If there is any error.
conn.rollback();
}
在这种情况下,上述 INSERT 语句都不会成功,并且所有内容都将被回滚。
以下是利用上述 commit 和 rollback 的示例。
此示例代码基于先前章节中完成的环境和数据库设置编写。
将以下示例复制并粘贴到 TestApplication.java 中,如下进行编译和运行:
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
public class TestApplication {
static final String DB_URL = "jdbc:mysql://localhost/TUTORIALSPOINT";
static final String USER = "guest";
static final String PASS = "guest123";
static final String QUERY = "SELECT id, first, last, age FROM Employees";
static final String INSERT_QUERY = "INSERT INTO Employees (first, last, age) values('Rita', 'Tez', 20)";
static final String INSERT_QUERY_2 = "INSERT INTO Employees (first, last, age) values('Sita', 'Singh', 20)";
public static void printResultSet(ResultSet rs) throws SQLException{
// Ensure we start with first row
rs.beforeFirst();
while(rs.next()){
// Display values
System.out.print("ID: " + rs.getInt("id"));
System.out.print(", Age: " + rs.getInt("age"));
System.out.print(", First: " + rs.getString("first"));
System.out.println(", Last: " + rs.getString("last"));
}
System.out.println();
}
public static void main(String[] args) {
Connection conn = null;
Statement stmt = null;
try{
// Open a connection
System.out.println("Connecting to database...");
conn = DriverManager.getConnection(DB_URL,USER,PASS);
// Set auto commit as false.
conn.setAutoCommit(false);
// Execute a query to create statment with
// required arguments for RS example.
System.out.println("Creating statement...");
stmt = conn.createStatement(
ResultSet.TYPE_SCROLL_INSENSITIVE,
ResultSet.CONCUR_UPDATABLE);
// INSERT a row into Employees table
System.out.println("Inserting one row....");
stmt.executeUpdate(INSERT_QUERY);
// INSERT one more row into Employees table
stmt.executeUpdate(INSERT_QUERY_2);
// Commit data here.
System.out.println("Commiting data here....");
conn.commit();
// Now list all the available records.
String sql = "SELECT id, first, last, age FROM Employees";
ResultSet rs = stmt.executeQuery(sql);
System.out.println("List result set for reference....");
printResultSet(rs);
// Clean-up environment
rs.close();
stmt.close();
conn.close();
}catch(SQLException se){
se.printStackTrace();
// If there is an error then rollback the changes.
System.out.println("Rolling back data here....");
try{
if(conn!=null)
conn.rollback();
}catch(SQLException se2){
se2.printStackTrace();
}
}catch(Exception e){
e.printStackTrace();
}finally{
// finally block used to close resources
try{
if(stmt!=null)
stmt.close();
}catch(SQLException se2){
se2.printStackTrace();
}
try{
if(conn!=null)
conn.close();
}catch(SQLException se){
se.printStackTrace();
}
}
}
}
现在让我们如下编译上述示例:
C:\>javac TestApplication.java
C:\>
运行 TestApplication 时,它会生成以下结果:
C:\>java TestApplication
Connecting to database...
Creating statement...
Inserting one row....
Commiting data here....
List result set for reference....
ID: 1, Age: 23, First: Zara, Last: Ali
ID: 2, Age: 30, First: Mahnaz, Last: Fatma
ID: 3, Age: 35, First: Zaid, Last: Khan
ID: 4, Age: 33, First: Sumit, Last: Mittal
ID: 5, Age: 40, First: John, Last: Paul
ID: 6, Age: 20, First: Rita, Last: Tez
ID: 7, Age: 20, First: Sita, Last: Singh
C:\>