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Oracle® Database Platform Guide
11g Release 2 (11.2) for Microsoft Windows

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16 Developing Applications for Windows

This chapter points to sources of information on developing applications for Windows and outlines a procedure for building and debugging external procedures.

This chapter contains these topics:

Finding Information on Application Development for Windows

This section describes where to find information on developing applications specifically for Windows. These products are included on your Oracle Database Server media.

Java Enhancements

Oracle Database includes an integrated Java Virtual Machine and JIT Compiler. Oracle Database also provides Oracle Java Database Connectivity (JDBC) Drivers. For more information, refer to Oracle Database Java Developer's Guide and Oracle Database JDBC Developer's Guide.

ODP.NET

Oracle Data Provider for .NET (ODP.NET) is an implementation of a data provider for Oracle Database. ODP.NET uses Oracle native APIs to offer fast and reliable access to Oracle data and features from any .NET application. ODP.NET also uses and inherits classes and interfaces available in the Microsoft .NET Framework Class Library. For more information, refer to Oracle Data Provider for .NET Developer's Guide and My Oracle Support Note 726240.1.

Oracle Developer Tools for Visual Studio

The Oracle Developer Tools for Visual Studio (ODT) is a tightly integrated "Add-in" for Microsoft Visual Studio 2008, 2005, and 2003. ODT integrates with Visual Studio to make it easy to browse and edit Oracle schema objects using integrated visual designers and can automatically generate .NET code through a simple drag and drop. Developers can modify table data, execute Oracle SQL statements, edit and debug PL/SQL code, generate and edit SQL scripts, and develop and deploy .NET stored procedures. There are many more features included with these tools. For more information, visit the ODT Web home at

http://www.oracle.com/technetwork/developer-tools/visual-studio/overview/index-097110.html

Oracle Providers for ASP.NET

Beginning with .NET Framework 2.0, ASP.NET includes service providers that store state in databases. By storing this state in a database, applications can ensure high availability of data, while making the data equally available to all Web servers. For more information, refer to Oracle Providers for ASP.NET Developer's Guide for Microsoft Windows.

Support for Internet Applications

Oracle Database support for internet applications includes Oracle Portal, which enables you to publish your data to the Web, Oracle HTTP Server, and PL/SQL Embedded Gateway, which offers PL/SQL procedures stored in Oracle Database that can be started through browsers. For more information, refer to:

  • Oracle Portal Installation Guide and Tutorial

  • Oracle Enterprise Manager Grid Control Installation and Basic Configuration

    Note:

    Oracle Portal is available on a separate media and included with Oracle Database for Windows.

    Oracle Database provides built-in mechanisms that address the requirements of the largest PHP, Ruby, Python Web, and Rich Internet Applications. The features include extreme connectivity, scalability, caching, nonintrusive performance acceleration, advanced security, and high-availability.

Oracle Services For Microsoft Transaction Server

Oracle Database for Windows permits enhanced deployment of COM/COM+ components in Microsoft Transaction Server, using Oracle Database as the resource manager. For more information, refer to Oracle Services for Microsoft Transaction Server Developer's Guide for Microsoft Windows.

Oracle Objects for OLE

Oracle Objects for OLE (OO4O) provides easy access to data stored in Oracle Database servers with any programming or scripting language that supports the Microsoft COM Automation and ActiveX technology. These include Visual Basic, Visual C++, Visual Basic For Applications (VBA), IIS Active Server Pages (VBScript and JavaScript), and others. For more information, refer to Oracle Objects for OLE Developer's Guide for Microsoft Windows.

Oracle Provider for OLE DB

Refer to Oracle Provider for OLE DB Developer's Guide for Microsoft Windows for information on OLE DB.

Oracle ODBC Driver

Open Database Connectivity (ODBC) provides a common C programming interface for applications to access data from database management systems. Access to databases is managed by the ODBC Driver Manager. The driver manager provides the linkage between an ODBC application and an ODBC driver for a specific database management system.

Oracle ODBC Driver provides access to Oracle databases for applications written using the ODBC interface.

Oracle Technology Network has both OracleHome based ODBC driver and Instant Client enabled ODBC driver.

Note:

Download Instant Client enabled ODBC driver from

http://www.oracle.com/technetwork/database/features/instant-client/index.html

Note:

Oracle ODBC Driver is updated on a regular basis. The newest release available is included on your media. To download the latest release, visit: http://www.oracle.com/technology/index.html

Select Oracle ODBC Drivers from the Select a Utility or Driver list.

Oracle COM Automation Feature

Oracle COM automation feature enables PL/SQL and Java stored procedure developers and COM/COM+ developers to load COM/COM+ objects from Oracle Database. For more information, refer to Oracle COM Automation Feature Developer's Guide for Microsoft Windows.

Pro*C/C++ and Pro*COBOL Applications

Refer to the following guides for more information on Pro*C/C++ and Pro*COBOL applications:

Building External Procedures

This section describes how to create and use external procedures on Windows. The following files are located in ORACLE_HOME\rdbms\extproc:

External Procedures Overview

External procedures are functions written in a third-generation language (C, for example) and callable from within PL/SQL or SQL as if they were a PL/SQL routine or function. External procedures let you take advantage of strengths and capabilities of a third-generation programming language in a PL/SQL environment.

Note:

Oracle Database also provides a special purpose interface, the call specification, that lets you call external procedures from other languages, as long as they are callable by C.

The main advantages of external procedures are:

  • Performance, because some tasks are performed more efficiently in a third-generation language than in PL/SQL, which is better suited for SQL transaction processing

  • Code re-usability, because dynamic link libraries (DLLs) can be called directly from PL/SQL programs on the server or in client tools

You can use external procedures to perform specific processes:

  • Solving scientific and engineering problems

  • Analyzing data

  • Controlling real-time devices and processes

Caution:

Special security precautions are warranted when configuring a listener to handle external procedures. See "Modifying Configuration of External Procedures for Higher Security" and Oracle Database Net Services Administrator's Guide for more information.

To create and use an external procedure, perform the following sequential steps:

Installing and Configuring

This section describes installation and configuration of Oracle Database and Oracle Net.

Installing Oracle Database

Follow the steps in Oracle Database Installation Guide for Microsoft Windows to install these products on your Windows server:

  • Oracle Database Enterprise Edition, Oracle Database Standard Edition, or Oracle Database Personal Edition. Each type contains PL/SQL, from which external procedures are called, and the PL/SQL external procedure program (EXTPROC), which runs external procedures.

  • Oracle Net Services

  • Oracle Protocol Support

Configuring Oracle Net Services

During database server installation, Oracle Net Configuration Assistant configures listener.ora and tnsnames.ora files for external procedure calls.

When an application calls an external procedure, Oracle Net Listener starts an external procedure agent called EXTPROC. Using a network connection established by the listener, the application passes the following information to EXTPROC:

  • DLL name

  • External procedure name

  • Parameters (if necessary)

EXTPROC then loads the DLL, runs the external procedure, and passes back any values returned by the external procedure.

If you overwrite default listener.ora and tnsnames.ora files, then you must manually configure the following files for the external procedure behavior described previously to occur:

Writing an External Procedure

Using a third-generation programming language, you can write functions to be built into DLLs and started by EXTPROC. The following is a simple Microsoft Visual C++ example of an external procedure called FIND_MAX:

Note:

Because external procedures are built into DLLs, they must be explicitly exported. In this example, the DLLEXPORT storage class modifier exports the function FIND_MAX from a dynamic link library.
#include <windows.h>
#define NullValue -1
/*
  This function tests if x is at least as big as y.
*/
long __declspec(dllexport) find_max(long   x, 
                                short   x_indicator, 
long    y, 
short y_indicator, 
                                short *ret_indicator)
{
   /* It can be tricky to debug DLL's that are being called by a process
      that is spawned only when needed, as in this case.  
      Therefore try using the DebugBreak(); command.  
      This will start your debugger.  Uncomment the line with DebugBreak(); 
      in it and you can step right into your code.
   */
   /* DebugBreak();  */

   /* First check to see if you have any nulls. */
   /* Just return a null if either x or y is null. */

   if ( x_indicator==NullValue || y_indicator==NullValue) {
      *ret_indicator = NullValue;   
      return(0);
   } else { 
      *ret_indicator = 0;       /* Signify that return value is not null. */
      if (x >= y) return x;
      else return y;
   }
}

Building a DLL

After writing your external procedure(s) in a third-generation programming language, use the appropriate compiler and linker to build a DLL, making sure to export the external procedures as noted previously. See your compiler and linker documentation for instructions on building a DLL and exporting its functions.

You can build the external procedure FIND_MAX, created in "Writing an External Procedure", into a DLL called extern.dll by going to ORACLE_HOME\rdbms\extproc and typing make. After building the DLL, you can move it to any directory on your system.

Starting with Oracle9i Release 2, however, the default behavior of EXTPROC is to load DLLs only from ORACLE_HOME\bin or ORACLE_HOME\lib. To load DLLs from other directories, you must set environment variable EXTPROC_DLLS to a colon (:) separated list of DLL names qualified with their complete paths. The preferred way to set this environment variable is through the ENVS parameter in listener.ora.

See Also:

Oracle Database Advanced Application Developer's Guide for more information on EXTPROC

Registering an External Procedure

Once you have built a DLL containing your external procedure(s), you must register your external procedure(s) with Oracle Database:

To create a PL/SQL library to map to the DLL:

  1. Set environment variable EXTPROC_DLLS in the ENVS parameter in listener.ora. For example:

    SID_LIST_LISTENER =
     (SID_LIST =
      (SID_DESC =
       (SID_NAME=PLSExtProc)
       (ENVS=EXTPROC_DLLS=C:\app\oracle\product\11.2.0\dbhome_1\rdbms\extproc\extern.dll)
       (ORACLE_HOME=C:\app\oracle\product\11.2.0\dbhome_1)
       (PROGRAM=extproc)
      )
     )
    
  2. Start SQL*Plus:

    C:\> sqlplus
    
  3. Connect to the database with appropriate username and password.

  4. Create the PL/SQL library using the CREATE LIBRARY command:

    SQL> CREATE LIBRARY externProcedures AS 'C:\app\oracle\product\11.2.0\dbhome_1\rdbms\ extproc\extern.dll';
    

    where externProcedures is an alias library (essentially a schema object in the database), and

    C:\app\oracle\product\11.2.0\dbhome_1\rdbms\extproc\extern.dll
    

    is the path to the Windows operating system dllextern.dll. This example uses C:\app\oracle\product\11.2.0 as your Oracle base and dbhome_1 as your Oracle home.

    Note:

    The DBA must grant the EXECUTE privilege on the PL/SQL library to users who want to call the library's external procedure from PL/SQL or SQL.
  5. Create a PL/SQL program unit specification.

    Do this by writing a PL/SQL subprogram that uses the EXTERNAL clause instead of declarations and a BEGIN...END block. The EXTERNAL clause is the interface between PL/SQL and the external procedure. The EXTERNAL clause identifies the following information about the external procedure:

    • Name

    • DLL alias

    • Programming language in which it was written

    • Calling standard (defaults to C if omitted)

    In the following example, externProcedures is a DLL alias. You need the EXECUTE privilege for this library. The external procedure to call is find_max. If enclosed in double quotation marks, it becomes case-sensitive. The LANGUAGE term specifies the language in which the external procedure was written.

    CREATE OR REPLACE FUNCTION PLS_MAX(
      x BINARY_INTEGER,
      y BINARY_INTEGER)
    RETURN BINARY_INTEGER AS
      EXTERNAL LIBRARY externProcedures
      NAME "find_max"
      LANGUAGE C
      PARAMETERS (
        x long,                  -- stores value of x
        x_INDICATOR short,       -- used to determine if x is a NULL value
        y long,                  -- stores value of y
        y_INDICATOR short,        -- used to determine if y is a NULL value
      RETURN INDICATOR short );  -- need to pass pointer to return value's
                                 -- indicator variable to determine if NULL
    -- This means that my function will be defined as:
        -- long max(long x, short x_indicator,
        -- long y, short y_indicator, short * ret_indicator)
    

Restricting Library-Related Privileges to Trusted Users Only

The CREATE LIBRARY, CREATE ANY LIBRARY, ALTER ANY LIBRARY, and EXECUTE ANY LIBRARY privileges, and grants of EXECUTE ON library_name convey a great deal of power to users. If you plan to create PL/SQL interfaces to libraries, only grant the EXECUTE privilege to the PL/SQL interface. Do not grant EXECUTE on the underlying library. You must have the EXECUTE privilege on a library to create the PL/SQL interface to it. However, users have this privilege implicitly on libraries that they create in their own schemas. Explicit grants of EXECUTE ON library_name are rarely required. Only make an explicit grant of these privileges to trusted users, and never to the PUBLIC role.

Executing an External Procedure

To run an external procedure, you must call the PL/SQL program unit (that is, the alias for the external function) that registered the external procedure. These calls can appear in any of the following:

  • Anonymous blocks

  • Standalone and packaged subprograms

  • Methods of an object type

  • Database triggers

  • SQL statements (calls to packaged functions only)

In "Registering an External Procedure", PL/SQL function PLS_MAX registered external procedure find_max. Follow these steps to run find_max:

  1. Call PL/SQL function PLS_MAX from a PL/SQL routine named UseIt:

    SET SERVER OUTPUT ON
    CREATE OR REPLACE PROCEDURE UseIt AS
                    a integer;
                    b integer;
                    c integer;
    BEGIN
                    a := 1;
                    b := 2;
                    c := PLS_MAX(a,b);
                    dbms_output.put_line('The maximum of '||a||' and '||b||' is  '||c);
    END;
    
  2. Run the routine:

    SQL> EXECUTE UseIt;
    

Multithreaded Agent Architecture

An agent process is started for each session to access a system at the same time leading to several thousand agent processes concurrently. The agent processes operate regardless of whether each individual agent process is actually active at the moment. Agent processes and open connections can consume a disproportionate amount of system resources. This problem is addressed by using multithreaded agent architecture.

The multithreaded agent architecture uses a pool of shared agent threads. The tasks requested by the user sessions are put in a queue and are picked up by the first available multithreaded agent thread. Because only a small percentage of user connections are active at a given moment, using a multithreaded architecture allows for more efficient use of system resources.

Debugging External Procedures

Usually, when an external procedure fails, its C prototype is faulty. That is, the prototype does not match the one generated internally by PL/SQL. This can happen if you specify an incompatible C data type. For example, to pass an OUT parameter of type REAL, you must specify float *. Specifying float, double *, or any other C data type will result in a mismatch.

In such cases, you might get a lost RPC connection to external procedure agent error, which means that agent extproc terminated abnormally because the external procedure caused a core dump. To avoid errors when declaring C prototype parameters, refer to Oracle Database Data Cartridge Developer's Guide.

Using Package DEBUG_EXTPROC

To help you debug external procedures, PL/SQL provides utility package DEBUG_EXTPROC. To install the package, run script dbgextp.sql, which you can find in the PL/SQL demo directory.

To use the package, follow instructions in dbgextp.sql. Your Oracle Database account must have EXECUTE privileges on the package and CREATE LIBRARY privileges.

To debug external procedures:

  1. From Windows Task Manager, in the Processes dialog, select ExtProc.exe.

  2. Right click, and select Debug.

  3. Click OK in the message window.

    If you have built your DLL in a debug fashion with Microsoft Visual C++, then Visual C++ is activated.

  4. In the Visual C++ window, select Edit > Breakpoints.

    Use the breakpoint identified in dbgextp.sql in the PL/SQL demo directory.

    See Also:

Accessing Text Files with UTL_FILE

Package UTL_FILE allows your PL/SQL programs to read and write operating system text files. It provides a restricted version of standard operating system stream file I/O, including open, put, get, and close operations. When you want to read or write a text file, you call the function fopen, which returns a file handle for use in subsequent procedure calls. For example, the procedure put_line writes a text string and line terminator to an open file, and the procedure get_line reads a line of text from an open file into an output buffer.

See Also:

Oracle Database PL/SQL Packages and Types Reference for more information on UTL_FILE

FSEEK, a UTL_FILE subprogram, adjusts the file pointer forward or backward within the file by the number of bytes specified. In order for UTL_FILE.FSEEK to work correctly, the lines in the file must have platform-specific line terminator characters. On Windows platforms the correct line terminator characters are <CR><LF>.

Accessing Web Data with Intercartridge Exchange

This section discusses the following topics:

Configuring Intercartridge Exchange

You must add a parameter to the registry before using Intercartridge Exchange.

  1. Start Registry Editor from the command prompt:

    C:\> regedit
    

    The Registry Editor window appears.

    Note:

    For another way to configure your registry, see "Managing Registry Parameters with regedit"
  2. Add HTTP_PROXY to the registry subkey of the Oracle home directory that you are using. The location of this parameter is determined by how many Oracle home directories are on your computer. If you have only one home directory, add HTTP_PROXY to

    HKEY_LOCAL_MACHINE\SOFTWARE\ORACLE\HOME0. 
    

    If you have multiple home directory, add it to

    HKEY_LOCAL_MACHINE\SOFTWARE\ORACLE\KEY_HOME_NAME 
    
  3. Choose Add Value from the Edit menu.

    The Add Value dialog appears.

    Description of http.gif follows
    Description of the illustration http.gif

  4. Type HTTP_PROXY in the Value Name field and REG_SZ in the Data Type field.

  5. Click OK.

  6. Type www-proxy.your-site in the String field.

    Description of http2.gif follows
    Description of the illustration http2.gif

In this example, the Web site is marketing.com. You will enter the domain name of your actual Web site.

Using Intercartridge Exchange

Intercartridge Exchange enables you to use a stored package called UTL_HTTP to make Hypertext Transfer Protocol (HTTP) calls from PL/SQL, SQL, and SQL*Plus statements.

UTL_HTTP can do both of the following:

  • Access data on the Internet

  • Call Oracle Web Application Server cartridges

UTL_HTTP contains two similar entry points, known as packaged functions, that turn PL/SQL and SQL statements into HTTP callouts:

  • UTL_HTTP.REQUEST

  • UTL_HTTP.REQUEST_PIECES

Both packaged functions perform the following tasks:

  • Take a string universal resource locator (URL) of a site

  • Contact that site

  • Return data (typically HTML) obtained from that site

Declarations to use with both packaged functions are described in the following subsections.

Packaged Function UTL_HTTP.REQUEST

UTL_HTTP.REQUEST uses a URL as its argument and returns up to the first 2000 bytes of data retrieved from that URL. Specify UTL_HTTP.REQUEST as follows:

FUNCTION REQUEST (URL IN VARCHAR2) RETURN VARCHAR2;

To use UTL_HTTP.REQUEST from SQL*Plus, enter:

SQL> SELECT UTL_HTTP.REQUEST('HTTP://WWW.ORACLE.COM/') FROM DUAL;

which returns:

UTL_HTTP.REQUEST('HTTP://WWW.ORACLE.COM/')                         
        ------------------------------------------------------
<html>
<head><title>Oracle Home Page</title>
<!--changed Jan. 16, 19
1 row selected.

Packaged Function UTL_HTTP.REQUEST_PIECES

UTL_HTTP.REQUEST_PIECES uses a URL as its argument and returns a PL/SQL table of 2000 bytes of data retrieved from the given URL. The final element can be shorter than 2000 characters. The UTL_HTTP.REQUEST_PIECES return type is a PL/SQL table of type UTL_HTTP.HTML_PIECES.

UTL_HTTP.REQUEST_PIECES, which uses type UTL_HTTP.HTML_PIECES, is specified as:

type html_pieces is table of varchar2(2000) index by binary_integer;
function request_pieces (url in varchar2,
  max_pieces natural default 32767)
return html_pieces;

A call to REQUEST_PIECES can look like this example. Note the use of PL/SQL table method COUNT to discover the number of pieces returned; it can be zero or more:

declare pieces utl_http.html_pieces;
begin 
  pieces := utl_http.request_pieces('http://www.oracle.com/'); 
   for i in 1 .. pieces.count loop
     .... -- process each piece
   end loop;
end;

The second argument to UTL_HTTP.REQUEST_PIECES (MAX_PIECES) is optional. MAX_PIECES is the maximum number of pieces (each 2000 characters in length, except for the last, which can be shorter) that UTL_HTTP.REQUEST_PIECES returns. If provided, that argument is usually a positive integer.

For example, the following block retrieves up to 100 pieces of data (each 2000 bytes, except perhaps the last) from the URL. The block prints the number of pieces retrieved and the total length, in bytes, of the data retrieved.

set serveroutput on

declare 
  x utl_http.html_pieces;
begin
  x := utl_http.request_pieces('http://www.oracle.com/', 100);
  dbms_output.put_line(x.count || ' pieces were retrieved.');
  dbms_output.put_line('with total length ');
  if x.count < 1 
  then dbms_output.put_line('0');
  else dbms_output.put_line
((2000 * (x.count - 1)) + length(x(x.count)));
  end if;
end;

which displays:
Statement processed.
4 pieces were retrieved.
with total length 
7687

Elements of the PL/SQL table returned by UTL_HTTP.REQUEST_PIECES are successive pieces of data obtained from the HTTP request to that URL.

UTL_HTTP Exception Conditions

This subsection describes exceptions (errors) that can be raised by packaged functions UTL_HTTP.REQUEST and UTL_HTTP.REQUEST_PIECES.

UTL_HTTP.REQUEST

PRAGMA RESTRICT_REFERENCES enables display of exceptions:

create or replace package utl_http is
function request (url in varchar2) return varchar2;
pragma restrict_references (request, wnds, rnds, wnps, rnps);

UTL_HTTP.REQUEST_PIECES

PRAGMA RESTRICT_REFERENCES enables display of exceptions:

create or replace package utl_http is
type html_pieces is table of varchar2(2000) index by binary_integer;
function request_pieces (url in varchar2, 
   max_pieces natural default 32767)
return html_pieces;
pragma restrict_references (request_pieces, wnds, rnds, wnps, rnps);

Exception Conditions and Error Messages

If initialization of the HTTP callout subsystem fails for environmental reasons (such as lack of available memory), then exception UTL_HTTP.INIT_FAILED is raised:

init_failed exception;

If the HTTP call fails due to failure of the HTTP daemon or because the argument to REQUEST or REQUEST_PIECES cannot be interpreted as a URL (because it is NULL or has non-HTTP syntax), then exception UTL_HTTP.REQUEST_FAILED is raised:

request_failed exception;

Unless explicitly caught by an exception handler, these first two exceptions are reported by a generic message that shows them as "user-defined" exceptions, even though they are defined in this system package:

ORA-06510: PL/SQL: unhandled user-defined exception

If any other exception is raised during processing of the HTTP request (for example, an out-of-memory error), then function UTL_HTTP.REQUEST or UTL_HTTP.REQUEST_PIECES reraises that exception.

If no response is received from a request to the given URL, because the function made no contact with a site corresponding to that URL, then a formatted HTML error message may be returned:

<HTML>
<HEAD>
<TITLE>Error Message</TITLE>
</HEAD>
<BODY>
<H1>Fatal Error 500</H1>
Can't Access Document: http://home.nothing.comm.
<P>
<B>Reason:</B> Can't locate remote host:  home.nothing.comm.
<P>
<P><HR>
<ADDRESS><A HREF="http://www.w3.org">
CERN-HTTPD3.0A</A></ADDRESS>
</BODY>
</HTML>

If UTL_HTTP.REQUEST or UTL_HTTP.REQUEST_PIECES raises an exception or returns an HTML-formatted error message, yet you believe that the URL argument is correct, try contacting that same URL with a browser to verify network availability from your computer.