Generating PDF Reports Using nfop

There are lots of articles, which describe how to convert XML documents to the documents of other types using the XSL Formatting Objects. Most of them describe how to obtain HTML from XML and only few tell about PDF documents.

Such articles usually demonstrate simple examples (how to build the table or perform the text output). But sometimes we need to create representative reports or documents. In this case, developers face nontrivial problems – for example creating the table of contents (using internal or external links), bookmark trees, picture galleries, etc. This article will help you to examine main features of XSL schemes.

1. Brief survey of the topic
2. С# example
3. XSL Features
4. Conclusion

Brief survey of the topic

Generation of PDF documents is based on the Apache XML FOP technology that was initially written in Java language. But in our case, we use nFOP – the C# wrapper that is based on the Visual J#. This wrapper makes it easier to write pure .NET reporting modules. The generation of PDF documents is very simple and can be described in the following way:

We have an XML document (created by some application or manually) and XSLT scheme, with the help of which we obtain the XSL-FO document. The PDF file will be created on its basis. Then we compile the obtained XSL-FO document to PDF with the help of FOP.

С# example

The process of PDF document generation can be described using a small example. Supposing, there is a list of writers, who have their books and these books consist of articles, respectively:

This structure is represented by Author and Book classes.

>public class Author
{
public List<Book> created;
public string name;
public int id;
...
}
public class Book
{
public int id;
public Props bookProps;
public List<Pare> articles;
...
}

C# language allows you to serialize any class to XML document. In this case, we can provide the following example:

//Serializing data
    FileStream fs = System.IO.File.Create("source.xml");
    XmlSerializer s = new XmlSerializer(typeof(List));
    List<Author> list = new List<Author>();
    list.Add(writer);
list.Add(writer1);
    s.Serialize(fs, list);
    fs.Close();

Then, according to the scheme described above, the process of XLS-FO document generation is performed:

//Generate FO file
    XslTransform xslt = new XslTransform();
    //Loading XSL template
    xslt.Load("schema.xsl");
    //Loading XSL template
    xslt.Transform("source.xml", "source.fo");

The last step is to call the methods of nfop, which compiles XLS-FO to PDF:

    //Generate PDF file
    java.io.FileInputStream streamFO = null;
    java.io.FileOutputStream streamOut = null;
    try
    {
        streamFO = new java.io.FileInputStream("source.fo");
        streamOut = new java.io.FileOutputStream(fileName + ".pdf");
        InputSource src = new InputSource(streamFO);
        Driver driver = new Driver(src, streamOut);
        driver.setRenderer(Driver.RENDER_PDF);
        driver.run();
    }
    catch(FOPException ex)
    {
        Console.WriteLine(ex.Message);
        throw;
    }
    catch (System.Exception ex)
    {
        Console.WriteLine(ex.Message);
        throw;
    }
    finally
    {
        if (streamOut != null)
        {
            streamOut.close();
        }
        if (streamFO != null)
        {
            streamFO.close();
        }
    }

It is important to include the following references to the solution being developed:

vjslib
nfop

vjslib.dll can be downloaded here.

nfop.dll can be downloaded here.

XSL Features

As it was mentioned above, the majority of articles about XSL-FO describe such common things as the output of the formatted text or the creation of tables. But often you need to add to the document:

Table of contents with internal references to articles (taking into account that we do not know the page numbers beforehand as the document is generated dynamically)
The bookmark tree (rather convenient tool for navigating in the document)
Footnotes with definite blocks of the text and, perhaps, references to external web pages
The picture gallery (it can be also dynamically saved by means of the C# language).

The bookmark tree.
Table of contents with internal references to chapters of the document.
Page numbering.
Static picture (can be the company logo).

Brief survey of main XSL operators and constructions

XSL language includes all main constructions:

if analog:

XML

<xsl:if test="'condition'">
<!--Operations-->
</xsl:if>

switch analog:

XML

<xsl:choose>
    <xsl:when test="'condition'">
        <!--Operations-->
        </xsl:when>
    <xsl:otherwise>
        <!--Operations-->
        </xsl:otherwise>
</xsl:choose>

for analog (processes a number of XML nodes with the same level of nesting):

XML

<xsl:value-of select="/Column[1]"></xsl:value-of>

Also you can use some variable as the index:

XML

<xsl:variable name="index">
    <xsl:value-of select="position()"></xsl:value-of>
</xsl:variable>
...
<xsl:value-of select="Column[number($index)]"></xsl:value-of>

number($index) conversion returns the number, which was generated from the string stored in $index. If you do not use it, the $index variable will possess “1” as any value as is considered to be of the string type by default.

If you use the position() operator it’s better to check also the condition:

XML

<xsl:if test="position() != last()">
    ...
    </xsl:if>

Here, position() is the number of the current node of the XML document (last() is the last in the list, respectively).

Usage of Cyrillic and East Asian fonts

There is often a problem of using specific languages in reports. By default, they are not included in the list of nfop fonts. To add new languages, you have to add a new font to the useconfig.xml file. The configuratiob file will look like the following:

XML

<fo:block>
    <xsl:attribute name="id">
        <xsl:value-of select="id"></xsl:value-of>
    </xsl:attribute>
</fo:block>

The process of building the tree is based on placing the blocks of such type:

C# <fo:leader leader-pattern=”dots”></fo:leader> <fo:page-number-citation> <xsl:attribute name=”ref-id”> <xsl:value-of select=”id”></xsl:value-of> </xsl:attribute> </fo:page-number-citation> </fo:basic-link>’ style=”color:#abb2bf;display:none” aria-label=”Copy” class=”code-block-pro-copy-button”>

<fo:basic-link>
    <xsl:attribute name="internal-destination">
        <xsl:value-of select="id"></xsl:value-of>
    </xsl:attribute>
    <xsl:text>Chapter 1</xsl:text><!--Name of link-->
    <fo:leader leader-pattern="dots"></fo:leader>
    <fo:page-number-citation>
        <xsl:attribute name="ref-id">
            <xsl:value-of select="id"></xsl:value-of>
        </xsl:attribute>
    </fo:page-number-citation>
</fo:basic-link>

The <fo:leader leader-pattern="dots"/> line fills space between the text and page number by dots.

Page numbering

One more interesting moment is that we do not know exactly on which page the table will be located while building the PDF document. Here we can use an expression that will define the page number of the dynamically generated document automatically:

XML

<fo:page-number-citation>
    <xsl:attribute name="ref-id">
        <xsl:value-of select="id"></xsl:value-of>
    </xsl:attribute>
</fo:page-number-citation>

Logo insertion

XSL Templates allow you to create the static content in any page region that will be repeated on each page. For example, the following code inserts the logo to the lower right corner of the document:

XML

<xsl:template name="ExternalLink">
    <xsl:param name="link"></xsl:param>
    <xsl:param name="link_text"></xsl:param>
    <fo:basic-link font-size="10pt" font-weight="bold" color="blue">
        <xsl:attribute name="external-destination">
            <xsl:value-of select="$link"></xsl:value-of>
        </xsl:attribute>
        <xsl:value-of select="$link_text"></xsl:value-of>
    </fo:basic-link>
</xsl:template>, was originally published on https://www.apriorit.com

Table rotation

There is often a problem of displaying the tables with numerous columns. Such tables cannot be placed within the page borders.

Name	Prop1	Prop2	Prop3	…	PropN
1	Some data	Some data	Some data	…	Some data
2	Some data	Some data	Some data	…	Some data

In this case, it is possible to perform table rotation, where a new table will correspond to each row:

Table 1 – first row

Name	1
Prop1	Some data
Prop2	Some data
Prop3	Some data
…	…
PropN	Some data

Table 2 – second row

Name	2
Prop1	Some data
Prop2	Some data
Prop3	Some data
…	…
PropN	Some data

Sometimes there is a nonstandard situation when it is necessary to process the data, which is stored in two related lists of nodes of the XML document. For example, you need to fill in the table where the first column Columns contains the name of the data, the second one – Rows – contains its values.

XML

  <columns>
        <column>
            Name
        </column>
        <column>
            Phone Number
        </column>
    </columns>
    <rows>
        <row>
            <value>
                <link>Johny
            </value>
            <value>
                <link>555-55-55
            </value>
        </row>
        <row>
            <value>
                <link>
                Ann
            </value>
            <value>
                <link>
                333-60-00
            </value>
        </row>
    </rows>

To create the table from the given XML document, you can use the following pattern:

XML

<xsl:template name="ParallelReading">
    <xsl:for-each select="Rows">
        <fo:table>
            <fo:table-column background-color="#DCDCDC" column-width="20%"></fo:table-column>
            <fo:table-column background-color="#FFFFFF"></fo:table-column>
            <fo:table-body>
                <xsl:for-each select="Row">
                    <fo:table-row>
                        <fo:table-cell padding="4pt" border="1pt solid black">
                            <xsl:for-each select="../../Columns/Column">
                                <fo:block>
                                    <xsl:value-of select="Title"></xsl:value-of>
                                </fo:block>
                            </xsl:for-each>
                        </fo:table-cell>
                        <fo:table-cell padding="4pt" border="1pt solid black">
                            <xsl:for-each select="Value">
                                <fo:block>
                                    <xsl:value-of select="Link"></xsl:value-of>
                                </fo:block>
                            </xsl:for-each>
                        </fo:table-cell>
                    </fo:table-row>
                </xsl:for-each>
            </fo:table-body>
        </fo:table>
    </xsl:for-each>
</xsl:template><br>

Gallery

The process of creating the picture gallery can be described in the following way:

The required pictures are saved to the temporary folder on the hard drive (programmatically).
The XML document is created. It contains the full paths and the description of the saved files (this data will be used later in the XSLT scheme).
The PDF document is generated. Pictures from the temporary folder are built in it.
The temporary folder with its contents is deleted.

XML

<galery xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
    <picture>
        <pare>
            <name>Name</name>
            <value>Blue hills</value>
        </pare>
        <pare>
            <name>Path</name>
            <value>E:/pdf_root/Blue hills.jpg</value>
        </pare>
        <pare>
            <name>Size</name>
            <value>28 521 bytes</value>
        </pare>
        <pare>
            <name>Type</name>
            <value>JPG File</value>
        </pare>
        <pare>
            <name>Created</name>
            <value>12 may 2010, 15:01:36</value>
        </pare>
    </picture>
    ...
</galery>

The pattern, which builds the gallery, is given below:

XML

<fo:block text-align="center" font-size="25pt">
    Gallery
</fo:block>
<fo:block>
 <fo:table>
   <fo:table-column></fo:table-column>
   <fo:table-body>
     <fo:table-row>
       <fo:table-cell padding="2pt" border="1pt solid indigo" background-color="silver">
        <fo:block>
          <fo:table>
         <fo:table-column column-width="1.5in"></fo:table-column>
         <fo:table-column></fo:table-column>
         <fo:table-body>
             <xsl:for-each select="Galery/Picture">
               <fo:table-row>
              <fo:table-cell padding="2pt" border="0.75pt solid black" background-color="lightgray">
                  <fo:block>
                        <fo:external-graphic display-align="center" content-height="scale-to-fit" height="1.5in" content-width="scale-to-fit">
                               <xsl:attribute name="src">
                                <xsl:value-of select="concat ('file:',Pare[number(2)]/Value)">
                               </xsl:value-of></xsl:attribute>
                           </fo:external-graphic>
                          </fo:block>
                      </fo:table-cell>
                      <fo:table-cell padding="2pt" border="0.75pt solid black" background-color="lightgray">
                          <fo:table>
                           <fo:table-column column-width="0.7in"></fo:table-column>
                           <fo:table-column></fo:table-column>
                           <fo:table-body>
                               <xsl:for-each select="Pare">
                                <fo:table-row>
                                 <fo:table-cell padding="2pt" border="0.5pt solid black" background-color="lavender">
                                     <fo:block font-size="7pt" padding="2pt">
                                      <xsl:value-of select="Name"></xsl:value-of>
                                     </fo:block>
                                 </fo:table-cell>
                                 <fo:table-cell padding="2pt" border="0.5pt solid black" background-color="lightgoldenrodyellow">
                                     <fo:block font-size="7pt" padding="2pt">
                                      <xsl:value-of select="Value"></xsl:value-of>
                                     </fo:block>
                                 </fo:table-cell>
                                </fo:table-row>
                               </xsl:for-each>
                           </fo:table-body>
                          </fo:table>
                      </fo:table-cell>
                     </fo:table-row>
                 </xsl:for-each>
                </fo:table-body>
               </fo:table>
           </fo:block>
          </fo:table-cell>
      </fo:table-row>
     </fo:table-body>
 </fo:table>
</fo:block>

As a result, we receive the following table:

Conclusion

In this article, we introduced a brief description of creating the PDF report using the existing data in the program. Also we gave a brief survey of main constructions and operators of the XSL language. There are a lot of simple but rather nonstandard situations when we need to transpose tables, move between levels in the XML document, and create picture galleries.

For additional information, see the following links:

Download example source (18,1KB)