Java使用JDBC-连接过多异常？

Question

i am trying to read data from url and storing in a string when i am storing that string value in my my sql table i am getting following Exception

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

How can i remove this Exception

Here is y code

public class DownLoadData {

    Statement st = null;
    Connection connection = null;
    String driverName = "com.mysql.jdbc.Driver";
    String serverName = "localhost";
    String schema = "mandi";
    String url1 = "jdbc:mysql://" + serverName + "/" + schema;
    String username = "root";
    String password = "";

    public void DownloadCommodity() throws ClassNotFoundException, SQLException {
        int j = 0;
        String htmlTableText = null;
        System.setProperty("webdriver.chrome.driver", "C:\\Users\\SHAKTI\\Desktop\\JarFiles\\chromedriver_win32\\chromedriver.exe");
        WebDriver driver = new ChromeDriver();
        String commodity = "Jo";
        String commo[] = {"Paddy", "Rice", "Jwar", "Barley", "Corn"
        };

        for (String com : commo) {
            String sDate = "27/03/2014";
            String url = "http://www.upmandiparishad.in/commodityWiseAll.aspx";
            driver.get(url);
            new Select(driver.findElement(By.id("ctl00_ContentPlaceHolder1_ddl_commodity"))).selectByVisibleText(com);
            driver.findElement(By.id("ctl00_ContentPlaceHolder1_txt_rate")).sendKeys(sDate);
            driver.findElement(By.id("ctl00_ContentPlaceHolder1_btn_show")).click();
            WebElement findElement = driver.findElement(By.id("ctl00_ContentPlaceHolder1_GridView1"));
            htmlTableText = findElement.getText();
      //  String html=find.getText();
            // do whatever you want now, This is raw table values.
            htmlTableText = htmlTableText.replace("S.No.DistrictMarketPrice", "");
            htmlTableText = htmlTableText.replaceAll("\\s(\\d+\\s[A-Z])", "\n$1");
            htmlTableText = htmlTableText.replaceAll("(?=(.*?[ ]){4,}).*?[\n\r]", "");
            htmlTableText = htmlTableText.replace("S.No. District Market Price", "");
            System.out.println(htmlTableText);
            String s[] = htmlTableText.split("");
            StringTokenizer str = new StringTokenizer(htmlTableText);
            while (str.hasMoreTokens()) // for(int i=0;i<s.length;i++)
            // if(str.hasMoreElements())
            {
                String no = str.nextElement().toString();

                String city = str.nextElement().toString();
                String mandi = str.nextElement().toString();
                String price = str.nextElement().toString();
                Class.forName(driverName);
                connection = DriverManager.getConnection(url1, username, password);
                PreparedStatement ps = connection.prepareStatement("insert into commoditydemo values(?,?,?,?,?,?)");
                ps.setString(1, no);
                ps.setString(2, city);
                ps.setString(3, mandi);
                ps.setString(4, price);
                ps.setString(5, com);
                ps.setString(6, "0");
                j = ps.executeUpdate();
                connection.close();

            }
        }
        driver.close();
        driver.quit();
        if (j == 1) {
            System.out.println("data inserted");
        } else {
            System.out.println("not inserted");
        }
    }

How can i get my correct output?

Thanks in advance

Answer 1

I suspect that the problem is opening and closing the database connection every iteration of the while loop. There is considerable clean up for the database to close a connection and you may be creating a backlog of close connection tasks that builds up faster than it is cleared.

It would be better to open a connection once in the method before the loop, do the work, then close the connection after the loop. You'll probably need a try-catch-finally around the use of the connection to ensure it is closed properly. If you are using java 7, use a try-resource block.

Answer 2

You are opening a connection repeatedly inside your while loop:

connection = DriverManager.getConnection(url1, username, password);

Try to place the establishing of connection outside(before) your loops. then close it after the loops are finished.

Answer 3

Try this code :
I have just initialized connection outside while loop.

public class DownLoadData {

    Statement st = null;
    Connection connection = null;
    String driverName = "com.mysql.jdbc.Driver";
    String serverName = "localhost";
    String schema = "mandi";
    String url1 = "jdbc:mysql://" + serverName + "/" + schema;
    String username = "root";
    String password = "";

    public void DownloadCommodity() throws ClassNotFoundException, SQLException {
        int j = 0;
        String htmlTableText = null;
        System.setProperty("webdriver.chrome.driver", "C:\\Users\\SHAKTI\\Desktop\\JarFiles\\chromedriver_win32\\chromedriver.exe");
        WebDriver driver = new ChromeDriver();
        String commodity = "Jo";
        String commo[] = {"Paddy", "Rice", "Jwar", "Barley", "Corn"
        };

        for (String com : commo) {
            String sDate = "27/03/2014";
            String url = "http://www.upmandiparishad.in/commodityWiseAll.aspx";
            driver.get(url);
            new Select(driver.findElement(By.id("ctl00_ContentPlaceHolder1_ddl_commodity"))).selectByVisibleText(com);
            driver.findElement(By.id("ctl00_ContentPlaceHolder1_txt_rate")).sendKeys(sDate);
            driver.findElement(By.id("ctl00_ContentPlaceHolder1_btn_show")).click();
            WebElement findElement = driver.findElement(By.id("ctl00_ContentPlaceHolder1_GridView1"));
            htmlTableText = findElement.getText();
      //  String html=find.getText();
            // do whatever you want now, This is raw table values.
            htmlTableText = htmlTableText.replace("S.No.DistrictMarketPrice", "");
            htmlTableText = htmlTableText.replaceAll("\\s(\\d+\\s[A-Z])", "\n$1");
            htmlTableText = htmlTableText.replaceAll("(?=(.*?[ ]){4,}).*?[\n\r]", "");
            htmlTableText = htmlTableText.replace("S.No. District Market Price", "");
            System.out.println(htmlTableText);
            String s[] = htmlTableText.split("");
            StringTokenizer str = new StringTokenizer(htmlTableText);
            connection = DriverManager.getConnection(url1, username, password);
            while (str.hasMoreTokens()) // for(int i=0;i<s.length;i++)
            // if(str.hasMoreElements())
            {
                String no = str.nextElement().toString();

                String city = str.nextElement().toString();
                String mandi = str.nextElement().toString();
                String price = str.nextElement().toString();
                Class.forName(driverName);

                PreparedStatement ps = connection.prepareStatement("insert into commoditydemo values(?,?,?,?,?,?)");
                ps.setString(1, no);
                ps.setString(2, city);
                ps.setString(3, mandi);
                ps.setString(4, price);
                ps.setString(5, com);
                ps.setString(6, "0");
                j = ps.executeUpdate();
                connection.close();

            }
        }
        driver.close();
        driver.quit();
        if (j == 1) {
            System.out.println("data inserted");
        } else {
            System.out.println("not inserted");
        }
    }

Answer 4

• Creating a new connection is a slow thing so if you can reuse it, do so.
• Prepared statements are intended to be reused. Read the API documentation for more info
• Make sure your connection is closed. The interface extends Autoclosable, use try with resources

Answer 5

If u want to do multiple inserts then better user batch and do insert.

try{
String queryString = "insert into commoditydemo values(?,?,?,?,?,?)";
        PreparedStatement ps = con.prepareStatement(queryString);

        while (str.hasMoreTokens()) // for(int i=0;i<s.length;i++)
            // if(str.hasMoreElements())
            {
                String no = str.nextElement().toString();

                String city = str.nextElement().toString();
                String mandi = str.nextElement().toString();
                String price = str.nextElement().toString();
                Class.forName(driverName);


                ps.setString(1, no);
                ps.setString(2, city);
                ps.setString(3, mandi);
                ps.setString(4, price);
                ps.setString(5, com);
                ps.setString(6, "0");
                ps.addBatch();
        }
        int[] rowsInsertedArray = ps.executeBatch();
        if(rowsInsertedArray.length != str.size()){throw new SQLException("Error in inserting users in commoditydemo");};
}
catch(SQLException e){
}
finally{
connection.close();
ps.close();
}

hope this will be helpful