使用JDBC从dbms_output.get_lines获取输出

Question

如何使用JDBC 从Java应用程序中获取Oracle dbms_output.get_lines的输出而不在数据库中创建其他对象？

Answer 1

I've also blogged about this issue here。这是一个片段，说明了如何做到这一点：

try (CallableStatement call = c.prepareCall(
    "declare "
  + "  num integer := 1000;" // Adapt this as needed
  + "begin "

  // You have to enable buffering any server output that you may want to fetch
  + "  dbms_output.enable();"

  // This might as well be a call to third-party stored procedures, etc., whose
  // output you want to capture
  + "  dbms_output.put_line('abc');"
  + "  dbms_output.put_line('hello');"
  + "  dbms_output.put_line('so cool');"

  // This is again your call here to capture the output up until now.
  // The below fetching the PL/SQL TABLE type into a SQL cursor works with Oracle 12c.
  // In an 11g version, you'd need an auxiliary SQL TABLE type
  + "  dbms_output.get_lines(?, num);"

  // Don't forget this or the buffer will overflow eventually
  + "  dbms_output.disable();"
  + "end;"
)) {
    call.registerOutParameter(1, Types.ARRAY, "DBMSOUTPUT_LINESARRAY");
    call.execute();

    Array array = null;
    try {
        array = call.getArray(1);
        System.out.println(Arrays.asList((Object[]) array.getArray()));
    }
    finally {
        if (array != null)
            array.free();
    }
}

以上将打印：

[abc, hello, so cool, null]

请注意，ENABLE / DISABLE设置是一个连接范围设置，因此您也可以通过多个JDBC语句执行此操作：

try (Connection c = DriverManager.getConnection(url, properties);
     Statement s = c.createStatement()) {

    try {
        s.executeUpdate("begin dbms_output.enable(); end;");
        s.executeUpdate("begin dbms_output.put_line('abc'); end;");
        s.executeUpdate("begin dbms_output.put_line('hello'); end;");
        s.executeUpdate("begin dbms_output.put_line('so cool'); end;");

        try (CallableStatement call = c.prepareCall(
            "declare "
          + "  num integer := 1000;"
          + "begin "
          + "  dbms_output.get_lines(?, num);"
          + "end;"
        )) {
            call.registerOutParameter(1, Types.ARRAY, "DBMSOUTPUT_LINESARRAY");
            call.execute();

            Array array = null;
            try {
                array = call.getArray(1);
                System.out.println(Arrays.asList((Object[]) array.getArray()));
            }
            finally {
                if (array != null)
                    array.free();
            }
        }
    }
    finally {
        s.executeUpdate("begin dbms_output.disable(); end;");
    }
}

另请注意，这将最多获取1000行的固定大小。如果需要更多行，可能需要循环PL / SQL或轮询数据库。

关于调用DBMS_OUTPUT.GET_LINE而非

的说明

以前，有一个现在已删除的答案，建议单独调用DBMS_OUTPUT.GET_LINE，一次返回一行。我对比较它与DBMS_OUTPUT.GET_LINES的方法进行了基准测试，差异很大 - 从JDBC调用时速度慢了30倍（即使从PL / SQL调用过程时没有太大的区别）。

因此，使用DBMS_OUTPUT.GET_LINES的批量数据传输方法绝对值得。这是基准的链接：

https://blog.jooq.org/2017/12/18/the-cost-of-jdbc-server-roundtrips/