java - 无法在java中从mysql导出csv文件

Question

我需要以CSV格式导出供用户下载的mysql表数据。

为了实现这一点，我正在尝试 java 运行时 exec 函数并执行“mysql -e”。不幸的是，我被困在一半了。我只能将 sql 输出显示到控制台，但无法将其路由到文件。

工作代码

(我可以在eclipse控制台中看到记录)

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();
    }

但是当我尝试使用 "> abc.txt " 将数据导出到文件时，该文件未创建，而是在 eclipse 控制台中看到 mySQL --help 选项。这里可能出了什么问题？

代码不工作

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 处理，而不是由每个程序处理。因此，mysql不知道如何处理> abc.txt。执行 shell 并将完整命令作为单个参数传递，就像这样在 Unix 系统中可以工作:

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"
});

但更好的选择(不采用 Unix shell)是使用 ProcessBuilder 和 redirectOutput(File) 方法。