因此，我试图通过引用位于不同 MYSQL 服务器中的表来运行在远程 MySQL 服务器中创建表的代码。我试图在其中创建表的服务器有空间限制，并且被引用的表非常大，因此它们必须保存在不同的远程服务器上。
我正在尝试找到一种方法来同时建立与两个数据库的持久连接（使用 JDBC 库），这样我就不必一直缓冲少量数据行......我希望能够直接引用数据。
例如，数据库 A 包含我引用的数据，而数据库 B 是我创建新表的位置。假设我在数据库 A 中引用的表是 1,000,000 行。而不是说，打开与数据库 A 的连接，缓冲 10,000 行，关闭连接，打开与数据库 B 的连接，写入该数据库，删除我的缓冲区，然后重复......
我只想与数据库 A 建立持久连接，因此每次写入数据库 B 都可以引用数据库 A 中的数据。
这可能吗？我尝试了几种方法（主要是通过创建仅在连接中断时才刷新的新连接对象），但我似乎无法让这个想法奏效。
有没有人使用 JDBC 做过类似的事情？如果是这样，如果你能指出我正确的方向，或者告诉我你是如何让它工作的，我将不胜感激。
我认为最好有两个单独的连接，一个读取连接和一个写入连接，并使用某种小型缓冲区通过您的 Java 应用程序传递数据。
另一个更复杂但可能更优雅的解决方案是使用 FEDERATED 表。它使远程服务器上的表看起来是本地的。查询被传递到远程服务器并将结果发回。您必须小心索引，否则它会非常慢，但它可能适用于您想要做的事情。
http://dev.mysql.com/doc/refman/5.5/en/federated-description.html
您可以在数据库 A 中创建数据，然后通过复制将其复制到数据库 B。
或者，听起来您正在实现某种队列。我曾经用 Java 构建了一个数据复制程序，它使用了 Queue 接口的内置实现。我有一个从数据库 A 读取数据并填充队列的线程，以及一个从队列读取数据并写入数据库 B 的线程。如果有用的话，我可以尝试挖掘我使用的类吗？
编辑：
这是代码，对发布进行了一些调整。我没有包含配置类，但它应该让您了解如何使用队列类；
package test;
import java.io.File;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.BlockingQueue;
/**
* This class implements a JDBC bridge between databases, allowing data to be
* copied from one place to another.
* <p>This implementation is threaded, as it uses a {@link BlockingQueue} to pass
* data between a producer and a consumer.
*/
public class DBBridge {
public static void main( String[] args ) {
Adaptor fromAdaptor = null;
Adaptor toAdaptor = null;
BridgeConfig config = null;
try {
/* BridgeConfig is essentially a wrapper around the Simple XML serialisation library.
* http://simple.sourceforge.net/
*/
config = BridgeConfig.loadConfig( new File( "db-bridge.xml" ) );
}
catch ( Exception e ) {
System.err.println( "Failed to read or parse db-bridge.xml: " + e.getLocalizedMessage() );
System.exit( 1 );
}
BlockingQueue<Object> b = new ArrayBlockingQueue<Object>( config.getQueueSize() );
try {
HashMap<String, DatabaseConfig> dbs = config.getDbs();
System.err.println( "Configured DBs" );
final String sourceName = config.getSource();
final String destinationName = config.getDestination();
if ( !dbs.containsKey( sourceName ) ) {
System.err.println( sourceName + " is not a configured database connection" );
System.exit( 1 );
}
if ( !dbs.containsKey( destinationName ) ) {
System.err.println( destinationName + " is not a configured database connection" );
System.exit( 1 );
}
DatabaseConfig sourceConfig = dbs.get( sourceName );
DatabaseConfig destinationConfig = dbs.get( destinationName );
try {
/*
* Both adaptors must be created before attempting a connection,
* as otherwise I've seen DriverManager pick the wrong driver!
*/
fromAdaptor = AdaptorFactory.buildAdaptor( sourceConfig, sourceConfig );
toAdaptor = AdaptorFactory.buildAdaptor( destinationConfig, destinationConfig );
System.err.println( "Connecting to " + sourceName );
fromAdaptor.connect();
System.err.println( "Connecting to " + destinationName );
toAdaptor.connect();
/* We'll send our updates to the destination explicitly */
toAdaptor.getConn().setAutoCommit( false );
}
catch ( SQLException e ) {
System.err.println();
System.err.println( "Failed to create and configure adaptors" );
e.printStackTrace();
System.exit( 1 );
}
catch ( ClassNotFoundException e ) {
System.err.println( "Failed to load JDBC driver due to error: " + e.getLocalizedMessage() );
System.exit( 1 );
}
DataProducer producer = null;
DataConsumer consumer = null;
try {
producer = new DataProducer( config, fromAdaptor, b );
consumer = new DataConsumer( config, toAdaptor, b );
}
catch ( SQLException e ) {
System.err.println();
System.err.println( "Failed to create and configure data producer or consumer" );
e.printStackTrace();
System.exit( 1 );
}
consumer.start();
producer.start();
}
catch ( Exception e ) {
e.printStackTrace();
}
}
public static class DataProducer extends DataLogger {
private BridgeConfig config;
private Adaptor adaptor;
private BlockingQueue<Object> queue;
public DataProducer(BridgeConfig c, Adaptor a, BlockingQueue<Object> bq) {
super( "Producer" );
this.config = c;
this.adaptor = a;
this.queue = bq;
}
@Override
public void run() {
/* The tables to copy are listed in BridgeConfig */
for ( Table table : this.config.getManifest() ) {
PreparedStatement stmt = null;
ResultSet rs = null;
try {
String sql = table.buildSourceSelect();
this.log( "executing: " + sql );
stmt = this.adaptor.getConn().prepareStatement( sql );
stmt.execute();
rs = stmt.getResultSet();
ResultSetMetaData meta = rs.getMetaData();
/* Notify consumer that a new table is to be processed */
this.queue.put( table );
this.queue.put( meta );
final int columnCount = meta.getColumnCount();
while ( rs.next() ) {
ArrayList<Object> a = new ArrayList<Object>( columnCount );
for ( int i = 0; i < columnCount; i++ ) {
a.add( rs.getObject( i + 1 ) );
}
this.queue.put( a );
}
}
catch ( InterruptedException ex ) {
ex.printStackTrace();
}
catch ( SQLException e ) {
// TODO Auto-generated catch block
e.printStackTrace();
}
try {
/* refresh the connection */
/* Can't remember why I can this line - maybe the other
* end kept closing the connection. */
this.adaptor.reconnect();
}
catch ( SQLException e ) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
try {
/* Use an object of a specific type to "poison" the queue
* and instruct the consumer to terminate. */
this.log( "putting finished object into queue" );
this.queue.put( new QueueFinished() );
this.adaptor.close();
}
catch ( InterruptedException e ) {
// TODO Auto-generated catch block
e.printStackTrace();
}
catch ( SQLException e ) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
/* Superclass for producer and consumer */
public static abstract class DataLogger extends Thread {
private String prefix;
public DataLogger(String p) {
this.prefix = p;
}
protected void log( String s ) {
System.err.printf( "%d %s: %s%n", System.currentTimeMillis(), this.prefix, s );
}
protected void log() {
System.err.println();
}
}
public static class DataConsumer extends DataLogger {
private BridgeConfig config;
private Adaptor adaptor;
private BlockingQueue<Object> queue;
private int currentRowNumber = 0;
private int currentBatchSize = 0;
private long tableStartTs = -1;
public DataConsumer(BridgeConfig c, Adaptor a, BlockingQueue<Object> bq) throws SQLException {
super( "Consumer" );
this.config = c;
this.adaptor = a;
this.queue = bq;
/* We'll send our updates to the destination explicitly */
this.adaptor.getConn().setAutoCommit( false );
}
public void printThroughput() {
double duration = ( System.currentTimeMillis() - this.tableStartTs ) / 1000.0;
long rowsPerSec = Math.round( this.currentRowNumber / duration );
this.log( String.format( "%d rows processed, %d rows/s", this.currentRowNumber, rowsPerSec ) );
}
@Override
public void run() {
this.log( "running" );
Table currentTable = null;
ResultSetMetaData meta = null;
int columnCount = -1;
PreparedStatement stmt = null;
while ( true ) {
try {
Object o = this.queue.take();
if ( o instanceof Table ) {
currentTable = (Table) o;
this.log( "processing" + currentTable );
if ( this.currentBatchSize > 0 ) {
/* Commit outstanding rows from previous table */
this.adaptor.getConn().commit();
this.printThroughput();
this.currentBatchSize = 0;
}
/* refresh the connection */
this.adaptor.reconnect();
this.adaptor.getConn().setAutoCommit( false );
/*
* Arguably, there's no need to flush the commit buffer
* after every table, but I like it because it feels
* tidy.
*/
this.currentBatchSize = 0;
this.currentRowNumber = 0;
if ( currentTable.isTruncate() ) {
this.log( "truncating " + currentTable );
stmt = this.adaptor.getConn().prepareStatement( "TRUNCATE TABLE " + currentTable );
stmt.execute();
}
this.tableStartTs = System.currentTimeMillis();
}
else if ( o instanceof ResultSetMetaData ) {
this.log( "received metadata for " + currentTable );
meta = (ResultSetMetaData) o;
columnCount = meta.getColumnCount();
String sql = currentTable.buildDestinationInsert( columnCount );
stmt = this.adaptor.getConn().prepareStatement( sql );
}
else if ( o instanceof ArrayList ) {
ArrayList<?> a = (ArrayList<?>) o;
/* One counter for ArrayList access, one for JDBC access */
for ( int i = 0, j = 1; i < columnCount; i++, j++ ) {
try {
stmt.setObject( j, a.get( i ), meta.getColumnType( j ) );
}
catch ( SQLException e ) {
/* Sometimes data in a shonky remote system
* is rejected by a more sane destination
* system. Translate this data into
* something that will fit. */
if ( e.getMessage().contains( "Only dates between" ) ) {
if ( meta.isNullable( j ) == ResultSetMetaData.columnNullable ) {
this.log( "Casting bad data to null: " + a.get( i ) );
stmt.setObject( j, null, meta.getColumnType( j ) );
}
else {
this.log( "Casting bad data to 0000-01-01: " + a.get( i ) );
stmt.setObject( j, new java.sql.Date( -64376208000L ), meta.getColumnType( j ) );
}
}
else {
throw e;
}
}
}
stmt.execute();
this.currentBatchSize++;
this.currentRowNumber++;
if ( this.currentBatchSize == this.config.getBatchSize() ) {
/*
* We've reached our non-committed limit. Send the
* requests to the destination server.
*/
this.adaptor.getConn().commit();
this.printThroughput();
this.currentBatchSize = 0;
}
}
else if ( o instanceof QueueFinished ) {
if ( this.currentBatchSize > 0 ) {
/* Commit outstanding rows from previous table */
this.adaptor.getConn().commit();
this.printThroughput();
this.log();
this.log( "completed" );
}
/* Exit while loop */
break;
}
else {
throw new RuntimeException( "Unexpected obeject in queue: " + o.getClass() );
}
}
catch ( InterruptedException e ) {
// TODO Auto-generated catch block
e.printStackTrace();
}
catch ( SQLException e ) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
try {
this.adaptor.close();
}
catch ( SQLException e ) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
public static final class QueueFinished {
/*
* This only exists as a completely type-safe value in "instanceof"
* expressions
*/
}
}
在我为工作而写的一个程序中，我有两个同时连接。在不泄露代码的情况下，您会想要
public void initialize() {
String dbUrl, dbUrl2, dbClass, dbClass2, user, user2, password, password2;
Connection con, con2;
Statement stmt, stmt2;
ResultSet rs, rs2;
try {
Class.forName(dbClass);
con = DriverManager.getConnection(dbUrl,user,password);
con2 = DriverManager.getConnection(dbUrl2,user2,password2);
stmt = con.createStatement();
} catch(ClassNotFoundException e) {
e.printStackTrace();
}
catch(SQLException e) {
e.printStackTrace();
}
}
然后，一旦您的两个连接运行，
rs = stmt.executeQuery("query");
rs2 = stmt2.executeQuery("second query");
我不知道如何具体解决您的问题，但此代码可能对您的系统有点负担（假设您没有高端个人/公司机器）并且可能需要一段时间。这至少应该给你足够的入门，如果可以的话，我会发布更多，遗憾的是模拟一个版本有点太复杂了。不过祝你好运！
我以前做过，我建议你做我所做的，即从 DB A 获取你需要的数据，并将其写入 1 个或多个文件作为 SQL 'set' 语句。当我这样做时，我不得不分成大约 10 个文件，因为在 DB B 中加载的文件大小受到限制