java - java连接MySQL数据库

Question

我正在使用一些用于多线程 MySQL 系统的代码。它工作正常，将在半秒内将条目放入我的数据库中。我的问题是，我的程序成功连接和写入数据库的速度并不快。有时它会正常工作，有时我会收到此错误或类似错误:

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

我真的不知道为什么会发生这种情况？从一个地址执行太多语句？无论如何，这是我的代码:

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();
    }
}

我没有包含的代码是不相关的，使用java.sql.Connection。有谁知道为什么会发生这种情况？谢谢。

Answer 1

完成后，您应该关闭语句和连接，否则资源池可能会耗尽或连接可能会超时。我建议从某些 JDBC 池获取新连接。几年前我曾经在servlet环境中使用proxool。如果你使用J2EE，那么应用服务器会为你做这件事，但你必须使用DataSource。