java - 来自服务器的错误 : Data source rejected establishment of connection, 消息: "Too many connections"

Question

我有一个文本文件，它的大小不是那么大 (600KB)，我的代码应该读取这个文件并将整个包含内容发送到我的数据库:

    private static void readBigFileAndSendToDB() throws Exception {
    Scanner s = new Scanner(new FileReader("tf1.txt"));
    while (s.hasNextLine()) {
        String eachLine = s.nextLine();   // each Line
        sendBigFileToDB(eachLine);
    }                                    // (end of file).
    System.out.println("Sent big file to DB");
    s.close();
}


    private static void sendBigFileToDB(String line) {
    Connection con = null;
    PreparedStatement ps = null;
    String query = "Insert into BigFile(text) values ('" + line + "')";

    try {
        if (line != null) {
            con = DriverManager.getConnection(...);
            ps = con.prepareStatement(query);
            ps.execute();
        }
    } catch (SQLException sqle) {
        sqle.printStackTrace();
    }
}

但是当我运行程序时，出现了这个异常:

com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Data source rejected establishment of connection,  message from server: "Too many connections"

Answer 1

当你获得一个连接时，你也需要关闭它。不关闭连接会导致资源泄漏，这最终可能会导致服务器拒绝连接，因为已达到最大连接数。

我建议您更改代码以使用 try-with-resources因此您的资源在使用范围结束时会自动关闭:

if (line == null) return;
String query = "Insert into BigFile(text) values (?)";

try (
    Connection con = con = DriverManager.getConnection(...);
    PreparedStatement ps = con.prepareStatement(query);
){
    ps.setString(1, line);
    ps.executeUpdate();
} catch (SQLException sqle) {
    sqle.printStackTrace();
}

请注意，我还通过正确使用准备好的语句参数将您的 line 连接替换为查询。

您的代码可以通过将连接创建和语句准备移到您的 readBigFileAndSendToDB 中进一步改进，这样它只完成一次并且不会在每次迭代时产生开销:

String query = "Insert into BigFile(text) values (?)";

try (
    Scanner s = new Scanner(new FileReader("tf1.txt"));
    Connection con = con = DriverManager.getConnection(...);
    PreparedStatement ps = con.prepareStatement(query);
){
    while (s.hasNextLine()) {
        String line = s.nextLine();
        if (line == null) continue;
        ps.setString(1, line);
        ps.addBatch();
    }
    ps.executeBatch();
} catch (SQLException sqle) {
    sqle.printStackTrace();
}