如何在Java中实现db侦听器 [英] How to implement a db listener in Java

问题描述

我有一个要求，如果一个记录插入一个数据库表，然后自动一个java进程需要执行。什么是实现数据库监听器的最简单的方法？

解决方案

我有一个Oracle解决方案。你不需要创建自己，因为现在Oracle买了Java，它为它发布了一个监听器。据我所知，这不在内部使用轮询，而是通知推送到Java端（可能基于一些触发器）：

  public interface oracle.jdbc.dcn.DatabaseChangeListener 
 extends java.util.EventListener {
 void onDatabaseChangeNotification（oracle.jdbc.dcn.DatabaseChangeEvent arg0）; 
} 
  

你可以像这样实现/ p>

  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，
通知对象上的错误，true）; 
 Util.printStackTrace（ex）; 
 Util.systemExit（）; 
} 
} 
} 
} 
  

strong> EDIT：

您可以使用以下类来注册： oracle.jdbc.OracleConnectionWrapper

  public class oracle.jdbc.OracleConnectionWrapper implements oracle.jdbc.OracleConnection {...} 
  

假设你在某个地方创建一个方法：

  public void registerPushNotification ）{
 oracle.jdbc.driver.OracleConnection oracleConnection = ...; //连接到db 
 
 dbProperties.setProperty（OracleConnection.DCN_NOTIFY_ROWIDS，true）; 
 dbProperties.setProperty（OracleConnection.DCN_QUERY_CHANGE_NOTIFICATION，true）; 
 
 //这是在db端实际注册的内容
 oracle.jdbc.dcn.DatabaseChangeRegistration dbChangeRegistration = oracleConnection.registerDatabaseChangeNotification（dbProperties）; 
 
 //现在你可以添加我的EDIT之前创建的监听器
 listener = new DBListener（this）; 
 dbChangeRegistration.addListener（listener）; 
 
 //现在你需要添加你想监视的表
语句stmt = oracleConnection.createStatement（）; 
 //将语句与注册相关联：
（（OracleStatement）stmt）.setDatabaseChangeRegistration（dbChangeRegistration）; //查找此方法的文档[http://docs.oracle.com/cd/E11882_01/appdev.112/e13995/oracle/jdbc/OracleStatement.html#setDatabaseChangeRegistration_oracle_jdbc_dcn_DatabaseChangeRegistration_] 
 
 ResultSet rs = stmt.executeQuery（sql）; //你必须执行查询以将其链接到要监视的语句
 while（rs.next（））{...如果感兴趣的话... do sth与结果...} 
 
 //查看正在监视的表
 String [] tableNames = dbChangeRegistration.getTables（）; 
 for（int i = 0; i< tableNames.length; i ++）{
 System.out.println（tableNames [i] +已经注册。 
} 
 rs.close（）; 
 stmt.close（）; 
} 
  

此示例不包括try-catch子句或任何异常处理。 p>

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 ?

解决方案

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);
}

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();                                       
            }
        }       
    }
}

EDIT:
You can use the following class to register: oracle.jdbc.OracleConnectionWrapper

public class oracle.jdbc.OracleConnectionWrapper implements oracle.jdbc.OracleConnection {...}

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();
}

This example does not include try-catch clauses or any exception handling.

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