连接到MySQL数据库Java

Question

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:

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

I'm really not sure why this happens? Executing too many statements from one address?? Anywho, here's my 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();
    }
}

The code I've not included is irrelevant, uses java.sql.Connection. Does anyone have any idea why this is occuring? Thanks.

Answer 1

You should close your statement and connection, once you are done, otherwise resource pool may be exhausted or your connection may time out. I recommend to obtain new connection from some JDBC pool. I used to use proxool few years ago in servlets environment. If you are in J2EE, then application server shall do it for you, but you have to use DataSource.