您好我正在编写一个需要与mysql数据库建立持久连接的java应用程序。我无权访问数据库服务器，因此无法更改数据库服务器上的任何内容，因此无法关闭连接。
我收到以下错误：
Exception in thread "main" com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure
The last packet successfully received from the server was 368,140 milliseconds ago. The last packet sent successfully to the server was 366,869 milliseconds ago.
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
at java.lang.reflect.Constructor.newInstance(Unknown Source)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:409)
at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1118)
at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:3055)
at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:2941)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3489)
at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1959)
at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2113)
at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2568)
at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:2113)
at com.mysql.jdbc.PreparedStatement.executeQuery(PreparedStatement.java:2275)
at SearchAndUpdate.recursiveUpdate(SearchAndUpdate.java:101)
at SearchAndUpdate.recursiveUpdate(SearchAndUpdate.java:110)
at SearchAndUpdate.recursiveUpdate(SearchAndUpdate.java:110)
at SearchAndUpdate.recursiveUpdate(SearchAndUpdate.java:110)
at SearchAndUpdate.recursiveUpdate(SearchAndUpdate.java:110)
at SearchAndUpdate.recursiveUpdate(SearchAndUpdate.java:110)
at SearchAndUpdate.recursiveUpdate(SearchAndUpdate.java:110)
at SearchAndUpdate.recursiveUpdate(SearchAndUpdate.java:110)
at SearchAndUpdate.recursiveTraversal(SearchAndUpdate.java:55)
at SearchAndUpdate.main(SearchAndUpdate.java:40)
Caused by: java.net.SocketException: Connection reset
at java.net.SocketInputStream.read(Unknown Source)
at com.mysql.jdbc.util.ReadAheadInputStream.fill(ReadAheadInputStream.java:114)
at com.mysql.jdbc.util.ReadAheadInputStream.readFromUnderlyingStreamIfNecessary(ReadAheadInputStream.java:161)
at com.mysql.jdbc.util.ReadAheadInputStream.read(ReadAheadInputStream.java:189)
at com.mysql.jdbc.MysqlIO.readFully(MysqlIO.java:2499)
at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:2952)
... 17 more
我假设此消息告诉我连接正在自动关闭。我不确定是否创建了持久连接......如果有人在java代码中给我一些指令，我将非常感激。非常感谢提前。
以下是我创建连接的代码：
import java.sql.*;
public class Connect
{
public static void main (String[] args)
{
Connection conn = null;
try
{
String userName = "sdfasdfsf";
String password = "asdfasdfsd";
String url = "jdbc:mysql://nameOfcomputer:3306/databasename";
Class.forName ("com.mysql.jdbc.Driver").newInstance();
conn = DriverManager.getConnection (url, userName, password);
System.out.println ("Database connection established");
}
catch (Exception e)
{
System.err.println ("Cannot connect to database server");
System.out.println(e.getMessage());
}
}
}
我刚刚在网上找到了以下示例：
http://www.java2s.com/Tutorial/Java/0340__Database/KeeptheConnectionAliveforMySQL.htm
这会是持久连接的一个例子吗？
我的代码通过使用我发布的相同代码来获取连接，并运行超过4个小时更新mysql中的表。应用程序基本上对目录进行递归搜索，查找所有文件并获取文件的信息，然后将信息输入数据库。该目录是搜索包含更多感谢100,000文件。连接有时会关闭，因为有时程序需要一段时间 递归查找文件，以下是我的代码：
public class Search{
public static void main(String[] args) throws SQLException
{
File fileObject = new File("scanLocation");
Connection conn = getConnection();
update(fileObject, conn);
conn.close();
}
public static void update(File fileObject, Connection conn)throws SQLException
{
if (fileObject.isDirectory())
{
File allFiles[] = fileObject.listFiles();
if (allFiles != null)
{
for (File aFile : allFiles)
{
if (aFile.isFile())
{
String filename=aFile.aFile.getName();
String query = "INSERT INTO table("
+ "File_Name" +")"
+ " Values (?)";
try
{ PreparedStatement psmt=conn.prepareStatement(query);
psmt.setString(1, fileName);
psmt.executeUpdate();
}
catch (SQLException e)
{
System.out.println("SQLExceptoin - " + e.getMessage());
System.out.println("SQLState: " + e.getSQLState());
System.out.println("VendorError: " + e.getErrorCode());
e.printStackTrace();
}
}
else
{
recursiveUpdate(aFile, conn);
}
}
}
}
}
public static Connection getConnection()
{
String DATABASE_USER = "user";
String DATABASE_PASSWORD = "password";
String MYSQL_AUTO_RECONNECT = "autoReconnect";
String MYSQL_MAX_RECONNECTS = "maxReconnects";
Connection conn = null;
try
{
String userName = "username";
String password = "password";
String url = "jdbc:mysql://compName:3306/database";
Class.forName("com.mysql.jdbc.Driver").newInstance();
conn = DriverManager.getConnection(url, userName, password);
java.util.Properties connProperties = new java.util.Properties();
connProperties.put(DATABASE_USER, userName);
connProperties.put(DATABASE_PASSWORD, password);
connProperties.put(MYSQL_AUTO_RECONNECT, "true");
connProperties.put(MYSQL_MAX_RECONNECTS, "4");
return DriverManager.getConnection(url, connProperties);
}
catch (Exception e)
{
System.err.println("Cannot connect to database server");
System.out.println(e.getMessage());
e.printStackTrace();
}
return conn;
}
}
程序有时会完成，有时数据库服务器强制关闭连接？由于我没有对数据库服务器的任何访问权限，我该怎么办才能使数据库服务器不关闭连接？
非常感谢
答案 0 :(得分：0)
好吧，如果您无法控制服务器何时关闭连接，那么您将不得不打开一个新连接。在这种情况下，您不能拥有真正的持久连接（尽管您可以为其创建一个外观） - 您必须检测到一个已关闭并重新打开一个连接。