看了下mysql-connector-5.1.40版本中，如果设置failoverReadOnly=true (即默认值，参考
链接)，当mysql连接failover时，会根据jdbc连接串将当前连接的readOnly值设置为true (第8行代码)
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private
synchronized
void
switchCurrentConnectionTo(
int
hostIndex, MySQLConnection connection)
throws
SQLException {
invalidateCurrentConnection();
boolean
readOnly;
if
(isPrimaryHostIndex(hostIndex)) {
readOnly =
this
.explicitlyReadOnly ==
null
?
false
:
this
.explicitlyReadOnly;
}
else
if
(
this
.failoverReadOnly) {
readOnly =
true
;
}
else
if
(
this
.explicitlyReadOnly !=
null
) {
readOnly =
this
.explicitlyReadOnly;
}
else
if
(
this
.currentConnection !=
null
) {
readOnly =
this
.currentConnection.isReadOnly();
}
else
{
readOnly =
false
;
}
syncSessionState(
this
.currentConnection, connection, readOnly);
this
.currentConnection = connection;
this
.currentHostIndex = hostIndex;
}
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当执行update操作时，如果检测到readonly，就会跑出createSQLException （第8-9行代码）
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protected
int
executeUpdate(
byte
[][] batchedParameterStrings, InputStream[] batchedParameterStreams,
boolean
[] batchedIsStream,
int
[] batchedStreamLengths,
boolean
[] batchedIsNull,
boolean
isReallyBatch)
throws
SQLException {
synchronized
(checkClosed().getConnectionMutex()) {
MySQLConnection locallyScopedConn =
this
.connection;
if
(locallyScopedConn.isReadOnly()) {
throw
SQLError.createSQLException(Messages.getString(
"PreparedStatement.34"
) + Messages.getString(
"PreparedStatement.35"
),
SQLError.SQL_STATE_ILLEGAL_ARGUMENT, getExceptionInterceptor());
}
....
}
}
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上述报错信息是PreparedStatement.34和PreparedStatement.35，查mysql connector的LocalizedErrorMessages.properties
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PreparedStatement.
34
=Connection is read-only.
PreparedStatement.
35
=Queries leading to data modification are not allowed
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报错信息一致。
因此， 如果是使用的主备mysql，需要手动切换master和slave，如果使用的是多主的mysql(例如，phxsql)，需要设置failoverReadOnly=false
![[Error] ‘for‘ loop initial declarations are only allowed in C99 mode](https://ucc.alicdn.com/images/user-upload-01/img_convert/45e886c36126f909b65535693c185792.png?x-oss-process=image/resize,h_160,m_lfit)