Java JDBC事务错误处理
建议使用以下代码Java JDBC事务错误处理,java,jdbc,transactions,Java,Jdbc,Transactions,建议使用以下代码 public void updateCoffeeSales(HashMap<String, Integer> salesForWeek) throws SQLException { PreparedStatement updateSales = null; PreparedStatement updateTotal = null; String updateString = "update " + dbName +
public void updateCoffeeSales(HashMap<String, Integer> salesForWeek)
throws SQLException {
PreparedStatement updateSales = null;
PreparedStatement updateTotal = null;
String updateString =
"update " + dbName + ".COFFEES " +
"set SALES = ? where COF_NAME = ?";
String updateStatement =
"update " + dbName + ".COFFEES " +
"set TOTAL = TOTAL + ? " +
"where COF_NAME = ?";
try {
con.setAutoCommit(false);
updateSales = con.prepareStatement(updateString);
updateTotal = con.prepareStatement(updateStatement);
for (Map.Entry<String, Integer> e : salesForWeek.entrySet()) {
updateSales.setInt(1, e.getValue().intValue());
updateSales.setString(2, e.getKey());
updateSales.executeUpdate();
updateTotal.setInt(1, e.getValue().intValue());
updateTotal.setString(2, e.getKey());
updateTotal.executeUpdate();
con.commit();
}
} catch (SQLException e ) {
JDBCTutorialUtilities.printSQLException(e);
if (con != null) {
try {
System.err.print("Transaction is being rolled back");
con.rollback();
} catch(SQLException excep) {
JDBCTutorialUtilities.printSQLException(excep);
}
}
} finally {
if (updateSales != null) {
updateSales.close();
}
if (updateTotal != null) {
updateTotal.close();
}
con.setAutoCommit(true);
}
}
public void updateCoffeeSales(HashMap salesForWeek)
抛出SQLException{
PreparedStatement updateSales=null;
PreparedStatement updateTotal=null;
字符串更新字符串=
更新“+dbName+”.coffes”+
“设置销售额=?其中COF_NAME=?”;
字符串更新语句=
更新“+dbName+”.coffes”+
“设置总计=总计+?”+
“其中COF_NAME=?”;
试一试{
con.setAutoCommit(假);
updateSales=con.prepareStatement(updateString);
updateTotal=con.prepareStatement(updateStatement);
对于(Map.Entry e:salesForWeek.entrySet()){
updateSales.setInt(1,e.getValue().intValue());
setString(2,例如getKey());
updateSales.executeUpdate();
updateTotal.setInt(1,e.getValue().intValue());
setString(2,例如getKey());
updateTotal.executeUpdate();
con.commit();
}
}捕获(SQLE异常){
jdbcttutorialutilities.printSQLException(e);
如果(con!=null){
试一试{
系统错误打印(“事务正在回滚”);
con.rollback();
}捕获(SQLException例外){
JDBCTutorialUtilities.printSQLException(excep);
}
}
}最后{
if(updateSales!=null){
updateSales.close();
}
if(updateTotal!=null){
updateTotal.close();
}
con.setAutoCommit(真);
}
}
然而,错误处理对我来说似乎是错误的
如果try块中存在NullPointerException,则不会捕获它。相反,执行将直接进入finally块,在那里它将调用con.setAutoCommit(true)
,这将提交任何正在进行的事务。似乎这显然不是预期的行为,因为它提交了一个不完整的事务
我认为这可能只是示例中的一个bug,但是除了SqlException()之外,还忘了捕获异常
我是否误解了正在发生的事情?在调用
con.setAutoCommit(true)
之前,该示例将关闭可能未完成的准备语句。因此,当切换回自动提交模式时,这些语句将不会执行。没有未完成的事务将在那里提交
我检查了您链接的第一个教程,它犯了一个错误,没有使用finally块,没有取消未完成的语句,也没有恢复自动提交模式。那看起来真的很粗心
总的来说,我建议坚持使用官方教程,或者使用您真正信任的资源。我倾向于认为您是对的;我的解决方案是不久前编写以下类,当出现意外异常时,该类将正确回滚。作为奖励,您可以将事务打包到一个try-with-resources块中,我发现这个块更可读,也更易于使用 你这样使用它:
try(Transaction trans = Transaction.create(conn)) {
// execute multiple queries, use trans.getConn()
trans.commit();
} catch (SQLException e) {
// Handle exception, transaction is safely rolled-back and closed
}
// No need for a finally block, or to catch RuntimeException.
下面是完整的课程:
import static com.google.common.base.Preconditions.checkState;
import java.sql.Connection;
import java.sql.SQLException;
/**
* A Transaction can be used in a try-with-resources block to ensure a set of queries are
* executed as a group.
*
* try(Transaction trans = Transaction.create(conn)) {
* // execute multiple queries, use trans.getConn()
* trans.commit();
* } catch (SQLException e) {
* // Handle exception, transaction is safely rolled-back and closed
* }
*/
public final class Transaction implements AutoCloseable {
private Connection conn;
private boolean committed = false;
private boolean rolledback = false;
/**
* Create a Transaction on the current connection, use to create
* a try-with-resources block.
*
* Note that if a transaction is started while another transaction is
* ongoing (i.e. conn.getAutoCommit() == true) the earlier transaction
* is committed.
*/
public static Transaction start(Connection conn) throws SQLException {
return new Transaction(conn);
}
private Transaction(Connection conn) throws SQLException {
this.conn = conn;
// this is a no-op if we're not in a transaction, it commits the previous transaction if we are
this.conn.setAutoCommit(true);
this.conn.setAutoCommit(false);
}
/**
* Call once all queries in the transaction have been executed,
* to indicate transaction is complete and ready to be committed.
* Should generally be the last line in the try block.
*/
public void commit() throws SQLException {
if(committed) {
throw new SQLException("Cannot commmit a transaction more than once");
}
if(rolledback) {
throw new SQLException("Cannot commit a previously rolled-back transaction");
}
committed = true;
getConn().commit();
}
/**
* Call explicitly to cancel the transaction, called implicitly
* if commit() is not called by the time the Transaction should
* be closed.
*/
public void rollback() throws SQLException {
if(rolledback) {
throw new SQLException("Cannot rollback a transaction more than once");
}
if(committed) {
throw new SQLException("Cannot rollback a previously committed transaction");
}
rolledback = true;
getConn().rollback();
}
/**
* Should not be called directly, called in the try-with-resources
* finally block to close the transaction.
*/
@Override
public void close() throws SQLException {
try {
if(!committed && !rolledback) {
conn.rollback();
throw new SQLException("Should explicitly rollback or commit transaction, rolling-back");
}
} finally {
conn.setAutoCommit(true);
conn = null;
}
}
/**
* Returns the Connection being used for this transaction. You are encouraged
* to use this method to access the transactional connection while inside the
* transaction's try-with-resources block.
*/
public Connection getConn() {
checkState(conn != null, "Connection has already been closed");
return conn;
}
}
我还没有公开这个类所属的项目的源代码,但是如果有人需要的话,我很乐意在麻省理工学院的许可下明确发布它。这似乎与这个问题中给出的答案不一致:如果错误发生在以下行:
updateSales.executeUpdate()
然后Jeremy is wright:finally块将提交由语句完成的更新(尽管给定了代码,但如果第一个语句没有,第二个语句将抛出NPE的可能性很小),在本例中,这可能不太可能,但是,对于某些人来说,在类似的代码中引入运行时异常
是完全可能的。实际上,我认为您可能是对的(至少,我有一些代码,在恢复自动提交之前显式回滚事务)。你能总结出这次失败的原因吗?我也认为你是对的。捕获Exception
比捕获SQLException
不一致更好,盲目捕获Exception
也会有同样的问题。显式捕获运行时异常、回滚和重试。