进行回滚的Java程序
调用回滚操作会撤消事务(T i ) 所做的所有影响或修改，并终止 T i并且所有变量都将存储其先前的值。回滚主要是在 Transaction(T i ) 的语句中出现一个或多个 SQL 异常时调用，然后 T i中止并从头开始。这是了解已提交和未提交的唯一方法。
SQL 异常只是表明您编写的语句中有问题，但没有提及错误的内容和位置。因此，留给您的唯一选择是调用回滚方法。
程序：它主要处理两个步骤。首先，创建一个数据库，然后处理事务。
- 创建数据库
- 执行回滚事务
- 导入数据库
- 必要时加载和注册驱动程序
- 创建新连接
- 创建提交/回滚语句
- 执行提交/回滚查询
- 处理结果
- 关闭连接，否则之前的处理可能会丢失（如果有的话）。
第 1 步：我们还可以通过将所需的保存点名称作为参数传递到以下方法中，将数据库中的修改回滚到特定标志或保存点 -
// Set the Flag or Save point
con.rollback("MysavePoint");步骤 2. 回滚事务：通过使用类的 API 方法forName(String className)加载 JDBC 驱动程序。在本例中，我们使用 Oracle
- 使用registerDriver( )方法注册所需的驱动程序
// To register the needed Driver
DriverManager.registerDriver(new com.mysql.jdbc.Driver());- 使用 DriverManager 的 getConnection() API 方法获取连接信息：
// For getting the connection
String url = "jdbc:mysql://localhost/mydatabase/icpc";
Connection conn = DriverManager.getConnection(string url, String user, String password);- 使用关闭连接 setAutoCommit(boolean auto-commit) 方法的 API 方法禁用自动提交，如下所示：
// Set the auto commit false. This will execute all
// SQL statements as individual transactions
con.setAutoCommit(false);- 现在，使用 setSavepoint() 设置保存点，或者使用连接的 API 方法 commit() 提交事务，如下所示 -
Savepoint savePoint = con.setSavepoint("MysavePoint");
Con.commit();- 如果发现任何 SQL 异常，那么在这种情况下，调用整个事务的 rollback() API 方法直到之前设置的保存点：
con.rollback() Or,
con. rollback(my_Savepoint);实现：同时演示rollback()和commit()程序的Java程序如下
Java
// Importing generic java libraries
import java.io.*;
// Retrieving SQL DB
// javaconnector-linkage for JDBC
import java.sql.*;
import java.sql.SQLException;
import java.sql.DriverManager;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.Statement;
import java.sql.PreparedStatement;
import java.sql.Date;
// Importing drivers(if necessarily)
// GFG class only to illustrate JDBC
// not illustrating connection class
class GFG {
/* Step 1: Importing DB */
// Database URL so as to create/fetch data from DB
static String DB_URL
= "jdbc:oracle:thin:@localhost/my_database_";
// DB userID
static String DB_USER = "local";
// Remember randomly self createdDB password
// to deal with above DB root
static String DB_PASSWORD = "test";
// Main driver method
public static void main(String args[])
{
// Try block to check exceptions if occurs
try {
/* Step 2: Loading and registering drivers*/
Class.forName(
"oracle.jdbc.driver.OracleDriver");
/* Step 3: Create the new connection */
Connection conn = DriverManager.getConnection(
DB_URL, DB_USER, DB_PASSWORD);
// set auto commit of the connection to false
conn.setAutoCommit(false);
/* Step 4: Create a statement */
// Input the info into record
String sql_
= "INSERT INTO Employee (empid, empname) VALUES (?, ?)";
// Create a Statement_object
PreparedStatement ps
= conn.prepareStatement(sql_);
/* Step 5: Execute a query */
// Take user input
BufferedReader br = new BufferedReader(
new InputStreamReader(System.in));
while (true) {
// Asking user to enter data(EmpID)
System.out.print("Enter emp_Id: ");
// Reading above user entered EmpID
String s_1 = br.readLine();
int empid = Integer.parseInt(s_1);
// Asking user to enter data(EmpName)
System.out.print("Enter emp_name: ");
// Reading above user entered EmpName
String name = br.readLine();
// Creating entry in table
// Set emp_id
ps.setInt(1, empid);
// Set emp_name
ps.setString(2, name);
// Execute the updation operation
ps.executeUpdate();
/* Step 6: Process the results */
/* Displaying choice what user wants to do
with updation, either Commit() or
rollback() */
System.out.println("commit or rollback");
// Reading choice from user
String answer = br.readLine();
/* Asking user's choice for condition
* check*/
/* Checking if users want to commit or
* rollback */
// If user wants to commit
if (answer.equals("commit")) {
conn.commit();
}
// If user wants to rollback
if (answer.equals("rollback")) {
// Rollback the update in case if some
// flaw in your record
conn.rollback();
}
/* Display message to user for inputing next
record if user wants to add */
System.out.println(
"Do you want to include more records");
/* Asking choice */
System.out.println("\n yes/no");
// Read user's choice
String answ = br.readLine();
if (answ.equals("no")) {
break;
}
}
conn.commit();
// Print message
System.out.println(
"record is successfully saved");
/* Step 7: Close the connection */
// calling commit() before closing connection
// else updation would be lost
conn.close();
}
// Exception handled if occured by catch block
catch (Exception exc) {
// Highlighting line where exception occured
// as execution is equal
exc.printStackTrace();
}
}
}输出：有两个示例输出图像涵盖了这两种情况：提交和回滚或直接回滚，如下面的输出所示。
