如何在 Java 中实现 db 侦听器 [英] How to implement a db listener in Java
问题描述
我有一个需求,如果一条记录插入到数据库表中,那么需要自动执行一个java进程.实现数据库监听器的最简单方法是什么?
I have a requirement where if a record is inserted in a db table , then automatically a java process needs to be executed.What is the easiest way to implement a db listener ?
推荐答案
我有一个针对 Oracle 的解决方案.您不需要创建自己的,因为 Oracle 购买了 Java,它为它发布了一个侦听器.据我所知,这在内部不使用轮询,而是将通知推送到 Java 端(可能基于某个触发器):
I have a solution for Oracle. You don't need to create your own since now that Oracle bought Java it released a listener for it. As far as I know this does not use polling internally, instead notifications are pushed to the Java side (probably based on some trigger):
public interface oracle.jdbc.dcn.DatabaseChangeListener
extends java.util.EventListener {
void onDatabaseChangeNotification(oracle.jdbc.dcn.DatabaseChangeEvent arg0);
}
你可以这样实现(这只是一个示例):
And you can implement it like this (this is just a sample):
public class DBListener implements DatabaseChangeListener {
private DbChangeNotification toNotify;
public BNSDBListener(DbChangeNotification toNotify) {
this.toNotify = toNotify;
}
@Override
public void onDatabaseChangeNotification(oracle.jdbc.dcn.DatabaseChangeEvent e) {
synchronized( toNotify ) {
try {
toNotify.notifyDBChangeEvent(e); //do sth
} catch (Exception ex) {
Util.logMessage(CLASSNAME, "onDatabaseChangeNotification",
"Errors on the notifying object.", true);
Util.printStackTrace(ex);
Util.systemExit();
}
}
}
}
您可以使用以下类进行注册:oracle.jdbc.OracleConnectionWrapper
public class oracle.jdbc.OracleConnectionWrapper implements oracle.jdbc.OracleConnection {...}
假设您在某处创建了一个方法:
Say you create a method somewhere:
public void registerPushNotification(String sql) {
oracle.jdbc.driver.OracleConnection oracleConnection = ...;//connect to db
dbProperties.setProperty(OracleConnection.DCN_NOTIFY_ROWIDS, "true");
dbProperties.setProperty(OracleConnection.DCN_QUERY_CHANGE_NOTIFICATION, "true");
//this is what does the actual registering on the db end
oracle.jdbc.dcn.DatabaseChangeRegistration dbChangeRegistration= oracleConnection.registerDatabaseChangeNotification(dbProperties);
//now you can add the listener created before my EDIT
listener = new DBListener(this);
dbChangeRegistration.addListener(listener);
//now you need to add whatever tables you want to monitor
Statement stmt = oracleConnection.createStatement();
//associate the statement with the registration:
((OracleStatement) stmt).setDatabaseChangeRegistration(dbChangeRegistration); //look up the documentation to this method [http://docs.oracle.com/cd/E11882_01/appdev.112/e13995/oracle/jdbc/OracleStatement.html#setDatabaseChangeRegistration_oracle_jdbc_dcn_DatabaseChangeRegistration_]
ResultSet rs = stmt.executeQuery(sql); //you have to execute the query to link it to the statement for it to be monitored
while (rs.next()) { ...do sth with the results if interested... }
//see what tables are being monitored
String[] tableNames = dbChangeRegistration.getTables();
for (int i = 0; i < tableNames.length; i++) {
System.out.println(tableNames[i] + " has been registered.");
}
rs.close();
stmt.close();
}
此示例不包含 try-catch 子句或任何异常处理.
This example does not include try-catch clauses or any exception handling.
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