SQL Server存储过程的输出参数被截断为4000个字符

Question

I have a problem with the output parameter of a stored procedure when it contains more than 4000 characters. The response seems to be truncated by the JDBC driver? How can I get the full result?

The stored procedure answers with the complete response (> 4000 characters) but I can not open it from Java. I have tried both jTDS and Microsoft's JDBC driver 6.0. Here is my code:

CallableStatement pstmt = con.prepareCall("{call sp_horus_get_consultorios_stv(?)}"); 
pstmt.registerOutParameter(1, -1); 
pstmt.setString(1, ""); 
pstmt.execute(); 
String sp_horus_get_consultorios_stv = pstmt.getString(1);

This works with stored procedures in sybase.

Answer 1

I was able to recreate your issue using Microsoft JDBC Driver 6.x. I found that I could avoid the problem by commenting out the setString call:

try (CallableStatement pstmt = conn.prepareCall("{call usp_horus_get_consultorios_stv(?)}")) {
    pstmt.registerOutParameter(1, Types.LONGNVARCHAR); 
    //pstmt.setString(1, "");  // disabled
    pstmt.execute(); 
    String sp_horus_get_consultorios_stv = pstmt.getString(1);
    System.out.println(sp_horus_get_consultorios_stv.length());  // > 4000 characters
}

Unfortunately, that fix did not solve the problem under jTDS 1.3.1. It appears that jTDS still suffers from the limitation described here . So, for jTDS it appears that we have to do something like this:

String sql = 
        "DECLARE @out NVARCHAR(MAX);" +
        "EXEC usp_horus_get_consultorios_stv @out OUTPUT;" +
        "SELECT @out;";
try (
        Statement st = conn.createStatement();
        ResultSet rs = st.executeQuery(sql)) {
    rs.next();
    String sp_horus_get_consultorios_stv = rs.getString(1);
    System.out.println(sp_horus_get_consultorios_stv.length());  // > 4000 characters
}

Answer 2

From what I understand, your output parameter is of type NVARCHAR(8000), which is the maximum explicit number allowed, and outputs a 4000 character Unicode string lenght (2 bytes per char).

However, and lucky you, there another possibility : NVARCHAR(MAX), that basically allows an infinite string lenght (well, not infinite, but almost : What is the maximum number of characters that nvarchar(MAX) will hold?

You should change your output paramater type to NVARCHAR(MAX).

Happy coding ;)