xml_ez_out

Langue: en

Version: 2009-12-27 (ubuntu - 25/10/10)

Section: 7 (Divers)

Sommaire

NAME

XML_EZ_Out - Simple Ada utility package for generating XML output.

SYNOPSIS

with McKae.XML.EZ_Out.Generic_Medium;
with McKae.XML.EZ_Out.String_Stream;
with McKae.XML.EZ_Out.Text_File;
package Ezsi is new Mckae.Xml.Ez_Out.Generic_Medium
(Output_Medium => File_Type,
Put => Put,
New_Line => New_Line[,
Format => Spread_Indented]);

DESCRIPTION

XML_EZ_Out is a small set of packages intended to aid the creation of XML-formatted output from within Ada programs. It basically wraps the tags and data provided to it with XML syntax and writes them to a user-supplied medium.

This medium can be any sort of writable entity, such as a file, a memory buffer, or even a communications link, such as a socket. The only functionality required of the medium is that it supply a meaningful "Put" (for writing a string) and "New_Line" procedure.

XML_EZ_Out package instantiations are explicitly designed to be made directly visible with the aid of a "use" clause. Declining to use a "use" will make using XML_EZ_Out inordinately verbose and awkward.

Generic Specification

 generic
 
    type Output_Medium is limited private;
    -- Output_Medium is whatever entity is going to received the formatted
    -- XML output. It can be a file, a stream, a buffer, a socket, whatever.
    -- All interaction with it takes place solely through the supplied Put and
    -- New_Line procedures, which are modeled after the Ada.Text_IO procedures.
 
    with procedure Put(F : in Output_Medium;
                       S : in String) is <>;
    -- Procedure writing a string to the instantiating output medium.
 
    with procedure New_Line
          (F       : in Output_Medium;
           Spacing : in Ada.Text_IO.Positive_Count := 1) is <>;
    -- Procedure writing a line break to the instantiating output medium.
 
    Format : Formatting_Options := Spread_Indented;
    -- Specify whether the XML being written is to be indented, i.e. be
    -- "prettified". (DEPRECATED, control formatting by setting the
    -- Current_Format variable available in the package spec.)
 
    Max_Element_Nesting : Positive := 200;
    -- The maximum element nesting depth of an XML document (used to set
    -- size of tag checking stack).
 
 package McKae.XML.EZ_Out.Generic_Medium;

Variables

Current_Format
The indentation format of the XML that is utilized. This can be altered at any time. Available settings are Continuous_Stream and Spread_Indented. (Supersedes deprecated generic parameter Format.)
Default_Output_Null_Attributes
Boolean indication whether to output an attribute if it has a null value.

Package Operations

See the Generic_Medium package specification for details of parameters and overloaded variations.
Output_XML_Header
Procedure to output a standard XML header line, as amended by the supplied arguments. To omit a standard attribute, pass an empty string as its value.
Output_Processing_Instruction
Add a processing instruction to the XML document.
Output_Element
Generate an entire element designated with the given tag and containing the provided content and attribute values.
Output_Tag
Generate an element tag containing zero or more attributes. By default the element is created using the compact, no-end-tag notation; to force generation of an element that has both start and end tags while containing no content, set End_Tag to True.
Start_Element
Initiate the generation of an XML element with the given tag and zero or more attribute values.
End_Element
Indicate the completion of the output of an XML element. If a Tag is specified, compare it against the element tag that is currently open, and raise Element_End_Mismatch if the two do not match. If there is no open element, then raise Element_Not_Open.
Output_Content
Place the text, as is, as the content of the currently open XML element. Output_Content can be called repeatedly, and will simply continue to append the additional content. If there is no open element, raise Element_Not_Open.
=
Associate an attribute name with a value. There are several overloaded variations of the "=" function for defining attribute name/value pairs. For each, the attribute name, Attr, can be of either the predefined Ada String type or the Unbounded_String type from Ada.Strings.Unbounded. The provided "=" functions accept a Value of a predefined Integer-based, Float-based, String, or Character type.

Errors

Element_Not_Open
An attempt was made to end, or add content to, an element when there were no open elements awaiting text or completion.
Element_End_Mismatch
The specified end tag does not match that of the currently open element.
Nesting_Too_Deep
The number of open, nested elements has exceeded the maximum level that was specified. Consider increasing the value of the Max_Element_Nesting generic parameter.
Invalid_Construction
An attempt was made to create a malformed document, such as inserting a process instruction into an open element.

Auxiliary Packages

McKae.XML.EZ_Out.Text_File
Mckae.XML.EZ_Out.Generic_Medium pre-instantiated with the
 predefined Ada.Text_IO.File_Type.
Mckae.XML.EZ_Out.String_Stream
McKae.XML.EZ_Out.Generic_Medium pre-instantiated with a limited functionality in-memory string buffering package, nested within the Mckae.XML.EZ_Out.String_Stream package as String_Buffering.

EXAMPLES

The key facilitator of making XML_EZ_Out usage readable when generating XML documentation is the overloading of a number of variations of the "=" function. By doing this, a simple XML element having no content, such as:

<player lastName="Cuddyer" firstName="Michael" team="Twins"/>

can be generated as:

 Output_Tag(F,
            "player",
            ("lastName"  = "Cuddyer",
             "firstName" = "Michael",
             "team"      = "Twins"));

To simplify the specification of the attributes, variations of "=" are provided. Given these declarations:

     Batting_Average : Float;
     At_Bats         : Natural;
One can directly reference the variables: 
 Output_Tag(F,
            "stats",
            ("battingAvg" = Batting_Average,
             "atBats"     = At_Bats));

NOTES

XML_EZ_Out is designed in such a way that instantiations of it are meant to be "used" by the application. When accompanied with a "use" clause, specifying the XML to be produced is very simple and clear. Insisting on using qualified names will make for very obtuse code. Likewise, "named parameter" notation would obscure the complementarity of the Ada and XML, so apply for a waiver from any such style standards.

The medium must be open and ready to accept content before invoking any of these XML output subprograms.

If the medium raises any exceptions as a result of invoking the supplied Put or New_Line procedures, those exceptions will be passed through to the caller.

AUTHOR

Marc A. Criley, McKae Technologies (mc@mckae.com)

CAVEATS

XML_EZ_Out does no validation of the XML content it is being asked to output, and it is possible to generate malformed documents. That includes the handling of character encoding. While XML_EZ_Out will claim the document is "UTF-8" or otherwise as set by the application, it is up to the application to ensure that correct content is provided in the strings that are passed to its various subprograms. Used appropriately, though, it can provide a clear and readable means to aid the dynamic generation of XML content by Ada programs.