Question

我有一个文本文件，它的大小不是很重（600KB），我的代码应该读取此文件并将整个包含发送到我的数据库：

    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，发生了这个异常：

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

Answer 1

获取连接后，您还需要关闭它。不关闭连接会导致资源泄漏，这可能最终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，以便在使用范围结束时自动关闭您的资源：

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，我还使用正确使用的预处理语句参数将line的串联替换为查询。

通过将连接创建和语句准备移动到readBigFileAndSendToDB中，您的代码可以进一步改进，因此它只执行一次，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();
}

Answer 2

完成流程后，请关闭声明和连接关闭：

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) {

    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();
    }
    finally {
        if (ps != null) try { ps .close(); } catch (SQLException logOrIgnore) {}
        if (con != null) try { con .close(); } catch (SQLException logOrIgnore) {}
        }
     }

错误：数据源拒绝建立连接，来自服务器的消息：＆＃34;连接太多＆＃34;

2 个答案: