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Oracle® Database Platform Guide 10g Release 2 (10.2) for Microsoft Windows (64-Bit) on Intel Itanium Part Number B14305-02 |
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# 15 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

- Developing Windows Applications

- Application Migration

- Building External Procedures

- Debugging External Procedures

- Accessing Text Files with UTL_FILE

- Accessing Web Data with Intercartridge Exchange

## 15.1 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 CD-ROM.

### 15.1.1 Java Enhancements

Oracle Database includes an integrated Java Virtual Machine and JServer Accelerator. Oracle Database also provides Oracle Java Database Connectivity (JDBC) Drivers. For more information, see Oracle Database Java Developer's Guide.

### 15.1.2 XML Support

Oracle XML products include XML Developer's Kit (XDK) and Oracle XML SQL Utility. For more information:

- Oracle XML Developer's Kit Programmer's Guide

- Oracle XML DB Developer's Guide

- Oracle Database XML Java API Reference

- Oracle Database XML C API Reference

- Oracle Database XML C++ API Reference

- Oracle Database SQL Reference

- Oracle Database PL/SQL Packages and Types Reference

### 15.1.3 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:

- Oracle Portal Installation Guide and Tutorial

- Oracle Enterprise Manager Grid Control Installation and Basic Configuration

  Note: Oracle Portal is not supported on Oracle Database for Microsoft Windows (64-Bit) on Intel Itanium.

### 15.1.4 Application Wizards

Oracle Application Wizards allow developers to create database applications easily and quickly. They improve ease-of-use and reduce development time by generating much of the code for database connectivity. For information and downloads, visit:

`http://www.oracle.com/technology/index.html`

### 15.1.5 Oracle COM/COM+ Integration Feature

Oracle COM/COM+ integration feature enables Java stored procedure developers and COM/COM+ developers to load COM+ objects from Oracle Database. For more information:

- Oracle COM Automation Feature Developer's Guide

### 15.1.6 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:

- Oracle Objects for OLE Developer's Guide

Note: Oracle Objects for OLE (OO4O) is not supported on Oracle Database 10g Release 2 (10.2) for 64-bit Windows.

### 15.1.7 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:

- Oracle Data Provider for .NET Developer's Guide

Note: Oracle Data Provider for .NET is not supported on Oracle Database 10g Release 2 (10.2) for 64-bit Windows.

### 15.1.8 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:

- Oracle Services for Microsoft Transaction Server Developer's Guide

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

- Pro*C/C++ Getting Started for Microsoft Windows

- Pro*COBOL Getting Started for Microsoft Windows

- Oracle Call Interface Programmer's Guide

Note: Pro*COBOL is not supported on Oracle Database for Microsoft Windows (64-Bit) on Intel Itanium.

### 15.1.10 OLE DB

- Oracle Provider for OLE DB Developer's Guide

  Note: Oracle ODBC Driver is updated on a regular basis. The newest release available is included on your CD-ROM. 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.

## 15.2 Developing Windows Applications

Oracle Database provides a comprehensive set of APIs for Windows application developers and is well suited for both Java and COM/COM+ development. Oracle Database is integrated with Microsoft's development and deployment components, known as Windows Distributed interNet Applications Architecture (DNA). Performance and data access on Windows is enhanced in the following areas:

- Wide variety of data access methods for Windows and internet applications

- Wizards and assistants to speed application development

- COM/COM+/DCOM integration through two APIs: Oracle Objects for OLE or Oracle Provider for OLE DB

- Microsoft Transaction Server integration: Oracle Services for Microsoft Transaction Server

- Platform extensions for internet application development

Developers are able to deploy their database applications more quickly by using the data access method with which they are familiar, rather than having to learn a new one. An Oracle Database server can communicate with Windows clients in a variety of methods, as described in Table 15-1.

Table 15-1 Oracle Data Access Methods

Development Environment | Data Access Method
--- | ---
Java | JDBC SQLJ
COM/COM+ | Oracle Objects for OLE (OO4O) Oracle Provider for OLE DB COM/COM+ Automation Feature

By using Oracle Database data access interfaces, developers can take advantage of specific Oracle Database features. These interfaces also offer flexibility and adherence to open standards.

Oracle COM/COM+ interfaces include the following features:

- OO4O can be used from any programming environment that supports Microsoft COM/COM+ technology, such as Visual Basic, Visual C++, VBA in Excel, Active Server Pages, PowerBuilder, Delphi, Internet Information Server (IIS), and Microsoft Transaction Server. OO4O is developed specifically for use with Oracle Database servers.

- Oracle Provider for OLE DB gives ActiveX Data Objects (ADO) developers high performance and efficient access to Oracle Database. A native OLE DB provider, it offers data access optimizations and access to Oracle-specific database features.

- COM/COM+ Automation Feature APIs make it easy for PL/SQL developers to incorporate COM/COM+ objects into their routines. An extension of this feature, Oracle COM/COM+ Integration, enables Java stored procedures and COM/COM+ developers to load COM/COM+ objects through OLE Automation or custom COM/COM+ interfaces in Oracle Database.

### 15.2.1 Developing Internet Applications

Oracle Database provides Windows extensions for internet development, enabling access from any client, such as:

- Any browser

- Windows or Macintosh client

- FTP client

- Database client

- COM/COM+ client

- E-mail client

Oracle Database data access interfaces and development tools, along with Microsoft Transaction Server integration, can be used to build internet applications, as illustrated in Figure 15-1, "Microsoft Transaction Server and Oracle Database Integration".

Figure 15-1 Microsoft Transaction Server and Oracle Database Integration

Description of "Figure 15-1 Microsoft Transaction Server and Oracle Database Integration"

## 15.3 Application Migration

Use Oracle 64-bit components to create your applications. To migrate your business logic, refer to Migration Tips on the Microsoft Developer Network (MSDN) Web site at `http://msdn.microsoft.com/default.asp`.

Note: `NCHAR` columns in user tables are not changed during the migration. To change `NCHAR` columns in user tables, refer to "Upgrade User NCHAR Columns" in Oracle Database Upgrade Guide.

## 15.4 Building External Procedures

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

- `extern.c` is the code example shown in "Writing an External Procedure"

- `make.bat` is the batch file that builds the dynamic link library

- `extern.sql` automates the instructions described in "Registering an External Procedure" and "Executing an External Procedure"

### 15.4.1 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

- Writing an External Procedure

- Building a DLL

- Registering an External Procedure

- Executing an External Procedure

  Note: You must have a C compiler and linker installed on your system to build DLLs.

  Note: You can combine the instructions described in the fourth and fifth tasks into one SQL script that automates the task of registering and executing your external procedure. See `ORACLE_BASE``\``ORACLE_HOME``\rdbms\extproc\extern.sql` for an example of a SQL script that combines these steps.

### 15.4.2 Installing and Configuring

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

#### 15.4.2.1 Installing Oracle Database

Follow the steps in Oracle Database Installation Guide for Microsoft Windows (64-Bit) on Intel Itanium 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

#### 15.4.2.2 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:

- `ORACLE_BASE``\``ORACLE_HOME``\network\admin\listener.ora`

- `ORACLE_BASE``\``ORACLE_HOME``\network\admin\tnsnames.ora`

  Caution: Additional security may be required for the listener in a production environment. See Oracle Database Net Services Administrator's Guide for more information.

### 15.4.3 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;
       }
    }

### 15.4.4 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_BASE``\``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 Application Developer's Guide - Fundamentals for more information on EXTPROC

### 15.4.5 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:\oracle\product\10.2.0\db_1\rdbms\extproc\extern.dll)
          (ORACLE_HOME=C:\oracle\product\10.2.0\db_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:\oracle\product\10.2.0\db_1\rdbms\ extproc\extern.dll';

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

       C:\oracle\product\10.2.0\db_1\rdbms\extproc\extern.dll

   is the path to the Windows operating system `dllextern.dll`. This example uses `C:\oracle\product\10.2.0` as your Oracle base and `db_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)

### 15.4.6 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;

## 15.5 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 datatype. For example, to pass an `OUT` parameter of type `REAL`, you must specify `float` `*`. Specifying `float`, `double` `*`, or any other C datatype 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.

### 15.5.1 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: `ORACLE_BASE``\``ORACLE_HOME``\rdbms\extproc\readme.doc` (explains how to run the sample and provides debugging advice) Oracle Database PL/SQL User's Guide and Reference Oracle Database Java Developer's Guide "Calling External Procedures" in Oracle Database Application Developer's Guide - Fundamentals Oracle Database Data Cartridge Developer's Guide

## 15.6 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>`.

## 15.7 Accessing Web Data with Intercartridge Exchange

This section discusses the following topics:

- Configuring Intercartridge Exchange

- Using Intercartridge Exchange

- UTL_HTTP Exception Conditions

- Exception Conditions and Error Messages

### 15.7.1 Configuring Intercartridge Exchange

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

1. Start Registry Editor from the command prompt:

       C:\> regedt

   The Registry Editor window appears.

   Note: For another way to configure your registry, see "Managing Registry Parameters with regedt"

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 more than one 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 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 the illustration http2.gif

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

### 15.7.2 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.

#### 15.7.2.1 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.

#### 15.7.2.2 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.

### 15.7.3 UTL_HTTP Exception Conditions

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

#### 15.7.3.1 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);

#### 15.7.3.2 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);

### 15.7.4 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.