stmt.setString(1, "a");    // This won't return any records

conn.prepareStatement("select * from x where c = cast(? as char(4))")

String sql = "select * from x where c = ?";
OraclePreparedStatement stmt = (OraclePreparedStatement) conn.prepareStatement(sql);
stmt.setFixedCHAR(1, "a");
...

I have nice fix for this.You have to add one property while getting connection from database.

NLS_LANG=american_america.AL32UTF8

or

In Java connection you can use below code :

java.util.Properties info = new java.util.Properties();
info.put ("user", user);
      info.put ("password",password);
      info.put("fixedString","TRUE");
      info.put("NLS_LANG","american_america.AL32UTF8");
      info.put("SetBigStringTryClob","TRUE");
      String url="jdbc:oracle:thin:@"+serverName;
      log.debug("url="+url);
      log.debug("info="+info);
        Class.forName("oracle.jdbc.OracleDriver");
        conn  = DriverManager.getConnection(url,info);


Thanks,
Swapna