無法從java中的mysql導出csv文件

Question

我要求導出用戶以CSV格式下載的mysql表數據。

為了實現這一點，我正在嘗試java運行時exec函數並執行“mysql -e”。 不幸的是，我被困在一半。 我只能將sql輸出顯示到控制台但不能將其路由到文件。

工作代碼

（我能在eclipse控制台中看到記錄）

try {
        Process p = Runtime.getRuntime().exec(new String[]
                {


                "mysql","-h","localhost","-u","admin","-pxyz","myDB","-e", "\"select concat(billing_amount,',') as 'Billing Amount,', concat(amount_paid ,',') as 'Amount Paid,' from invoice\""

                }
                );
         BufferedReader in = new BufferedReader(
                 new InputStreamReader(p.getInputStream()));
         String line = null;
         while ((line = in.readLine()) != null) {
                System.out.println(line);
            }
        //process.waitFor();
    } catch (Exception e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

但是當我嘗試使用“> abc.txt”將數據導出到文件時，不會創建該文件，而是在eclipse控制台中看到mySQL --help選項。 這可能有什么問題？

代碼不工作

try {
        Process p = Runtime.getRuntime().exec(new String[]
                {


                "mysql","-h","localhost","-u","admin","-pxyz","myDB","-e", "\"select concat(billing_amount,',') as 'Billing Amount,', concat(amount_paid ,',') as 'Amount Paid,' from invoice\"", "> abc.txt"

                }
                );
         BufferedReader in = new BufferedReader(
                 new InputStreamReader(p.getInputStream()));
         String line = null;
         while ((line = in.readLine()) != null) {
                System.out.println(line);
            }
        //process.waitFor();
    } catch (Exception e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

Answer 1

I / O重定向由shell處理，而不是由每個程序處理。 因此， mysql不知道如何處理> abc.txt 。 執行shell並將完整命令作為單個參數傳遞，就像在Unix系統中一樣：

Process p = Runtime.getRuntime().exec(new String[] {
     "sh", "-c", "mysql -h localhost -u admin -pxyz myDB -e \"select concat(billing_amount,',') as 'Billing Amount,', concat(amount_paid ,',') as 'Amount Paid,' from invoice\" > abc.txt"
});

但是，不假設Unix shell的更好選擇是使用ProcessBuilder和redirectOutput(File)方法。