JDBC Clob和NClob

Question

Is there any difference between java.sql.Clob and java.sql.NClob ? There is no new method for java.sql.NClob interface. I tried the following:

The setup SQL:

create table tab(id number(2), clobcol clob, nclobcol nclob)
insert into tab values (1, to_clob('你好'), to_nclob('你好'))

JDBC code:

conn = getConnection();
stmt = conn.createStatement();
rs = stmt.executeQuery("select * from tab");
rs.next();
Clob c = rs.getClob(2);
NClob nc = rs.getNClob(3);
InputStream inputStream1 = c.getAsciiStream();
InputStream inputStream2 = nc.getAsciiStream();
System.out.println(inputStream1.available());
System.out.println(inputStream2.available());
c.free();
nc.free();

I have also tried some other methods, looks like there is no difference from the output. Is there a specific I can see some differences ?

Added the supported character set in the database:

SELECT parameter, value
  FROM v$nls_parameters
  3   WHERE parameter LIKE '%CHARACTERSET';

PARAMETER             VALUE
--------------------------------- --------------------
NLS_CHARACTERSET          AL32UTF8
NLS_NCHAR_CHARACTERSET        AL16UTF16

Answer 1

In the old days (80s) many Databases were created using US7ASCII (in the US) or ISOLATIN1 (in Europe) as the character set. For these Databases that still exist today (after many upgrades), the only way to store non-ASCII character String data is to use the special types NVARCHAR or NCLOB. These Nxxx types are not used by newer Databases that were created directly using UTF8 (now the default in Oracle) as the encoding.