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POConnecting to MySQL database java
 

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  1. POConnecting to MySQL database java
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    <p>I'm using some code for multi threaded MySQL system. It's working fine and will put entry's into my database in under half a second. My problem is, the rate at which my program will successfully connect and write to the database, is not great. Some of the time it will work fine and other times I'll receive this error, or similar: </p> <pre><code>com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure The last packet successfully received from the server was 27,697 milliseconds ago. The last packet sent successfully to the server was 1 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:411) at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1121) at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:3670) at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:3559) at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:4110) at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2570) at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2731) at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2815) at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:2155) at com.mysql.jdbc.PreparedStatement.execute(PreparedStatement.java:1379) at MySQL.putEntry(MySQL.java:46) at MySQL.main(MySQL.java:105) Caused by: java.io.EOFException: Can not read response from server. Expected to read 4 bytes, read 0 bytes before connection was unexpectedly lost. at com.mysql.jdbc.MysqlIO.readFully(MysqlIO.java:3119) at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:3570) ... 9 more </code></pre> <p>I'm really not sure why this happens? Executing too many statements from one address?? Anywho, here's my code:</p> <pre><code>private final ThreadedSQL sql; private final DatabaseConnection connection; private PreparedStatement statement; public Hiscores() { try { loadConfig(); } catch (IOException e) { e.printStackTrace(); } sql = new ThreadedSQL(config); connection = sql.getConnectionPool().nextFree(); } public void putEntry(final Player player) { try { statement = connection.getConnection().prepareStatement(QUERY(player)); statement.execute(); statement.closeOnCompletion(); } catch(Exception e) { e.printStackTrace(); } } </code></pre> <p>The code I've not included is irrelevant, uses java.sql.Connection. Does anyone have any idea why this is occuring? Thanks.</p>
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    1. COI just wonder around this statement: prepareStatement(QUERY(player)); PreparedStatement shall be used when you have parameters to set.
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    2. COAre you sure that you free up your resources after use? You need to close result set, statement and connection in this order in finally block, otherwise various strange exceptions may occur. JDBC driver will hold some data and RDBMS may hold them as well. Try to clean up correctly.
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    3. COHi, thanks for commenting. The QUERY method is just a string and the player parameter is just for getting the name of the player and a few other fields. As for freeing up resources, I close the statement as you can see: statement.closeOnCompletion(). I didn't look into the method I just assumed that it closed it. I don't get a result set, should I be? I'm just putting data into a database, does that require a ResultSet? And finally do I have to close the connection, I wanted to keep it open and just keep executing statements through that one connection, maybe I should read documentation.Thanks
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