Author: Farrukh Mirza
Date: 13/07/2016
Location: Dublin, Republic of Ireland

Purpose

HTML-PDF-Service is a Java Spring Boot based microservice.
It exposes a RESTful interface to convert well-formed HTML Template to either PDF or well-formed HTML.
The service only expects HTML BODY contents to be sent over in the service calls under html parameter (HEAD section will be included by default).
The service allows the clients to optionally style the PDF output using CSS 2.1 style sheets.
The service also allows the clients to optionally use HTML as a Template with JSON data.

Even though there are many other similar projects available, the idea behind this microservice is to allow anyone to deploy it on existing Java based infrastructure within a public or private cloud environment.
The service allows the users to quickly build HTML page with custom styling, try it out from the web console and then simply insert variables in the HTML body which will be replaced by JSON object or JSON array provided as a separate argument to the service.
If a JSON array is provided with multiple JSON objects, then individual PDF outputs are merged together into a single PDF file and returned as such (try webconsole at {PROTOCOL}://{HOST:PORT}/html-pdf-service/).
In addition, this project also serves as a quick tutorial on building RESTful microservices and applications using Spring Boot in Java.

This service requires Servlet 3.0 servlet container like Tomcat 8 or Wildfly 9+.
This service uses:

1. Flying Saucer Pdf library to convert html and css documents (strings) into PDF.
2. Jackson to handle html templating with Json data.
3. Apache PDF Box to merge multiple pdf files into one.
4. JSON Path to traverse JSON data and parse values for templating.
5. Bootstrap to style web page.
6. JQuery to test and control page behaviour.
7. A few other pieces of javascript code were borrowed from different sources and converted into JQuery plugin. The original authors are acknowledged and credited in the respective files.

Licenses

html-pdf-service (this service) is provided under LGPL version 3 or later License. Third party licenses are listed below.

1. FlyingSaucer is provided under LGPL License version 3 which in turn uses iText 2.1.7 under Mozilla Public License Version 1.1.
2. spring-boot is provided under APACHE License v2
3. apache-commons-lang3 is provided under APACHE License v2
4. pdfbox is provided under APACHE License v2
5. jackson is provided under APACHE License v2
6. jsonpath 2.2.0 is provided under APACHE License v2 (Applicable expressions can be found at https://github.com/json-path/JsonPath)

Docker

Docker image is available at Docker Hub

docker pull farrukhmpk/html-pdf-service

Build

Pre-requisites

1. JDK8
2. Maven
3. Git 

Compile, build and deploy

By Default the service is built for Apache Tomcat server mvn clean install.
deploy.bat and run.bat can also be used to deploy the war file to Tomcat and run Tomcat server, assuming {CATALINA_HOME} is setup correctly. Linux versions of these scripts can be created very easily.

1. The service can be explicitly built for WildFly mvn clean install -Pwildfly.
2. The service can be explicitly built for Apache Tomcat. Build using mvn clean install -Ptomcat.
3. The service can be explicitly built for Embedded Tomcat Container. Build using mvn clean install -Pstandalone.

The main difference between the two profiles is the location of the log files.

Standalone deployment

This microservice can be very easily deployed as a standalone executable by enabling embedded Tomcat.

Simply build the project using standalone profile mvn clean install -Pstandalone and then run the resultant war java -jar target\html-pdf-service.war

Now you can access the test page by pointing your browser to http://localhost:8080/

Note: This, however, opens up the subject of port management in the production environment.

REST Endpoints

Endpoint Types

There are two types of endpoints.

1. Actual Endpoints.  
3. Management Endpoints (Spring Boot).  

Actual Endpoints

The service can be access from browser using {PROTOCOL}://{HOST:PORT}/html-pdf-service/. The main page serves as a testing area to try out different options.

The actual service endpoints use HTTP POST and GET protocols with slight variations.

The base endpoint for converting HTML Template into PDF is available at {PROTOCOL}://{HOST:PORT}/html-pdf-service/service/convert/html/
The service can be invoked in two fashions:

• The service can take the parameters in the request body by calling {PROTOCOL}://{HOST:PORT}/html-pdf-service/service/convert/html/body. In this case, the request body can contain a json object with html, css, json fields, where css and json fields are optional, e.g., {"html": "< h1 >This is a title</ h1 > < p >This is body</ p >", "css": "h1{color:blue;}"} . This only supports POST requests.
• The service can take the parameters as request parameters by calling {PROTOCOL}://{HOST:PORT}/html-pdf-service/service/convert/html/params. In this case, the request parameters contain html, css, json fields, where css and json fields are optional, e.g., html="< h1 >This is a title</ h1 > < p >This is body</ p >"&css="h1{color:blue;}" .

If the service response is desired as a byte stream, the service endpoint can be appended by /byte, e.g.,

• {PROTOCOL}://{HOST:PORT}/html-pdf-service/service/convert/html/body/byte
• {PROTOCOL}://{HOST:PORT}/html-pdf-service/service/convert/html/params/byte

The base endpoint for converting a HTML Template into Fully Formed HTML is available at {PROTOCOL}://{HOST:PORT}/html-pdf-service/service/template/html/
The service can be invoked in two fashions:

• The service can take the parameters in the request body by calling {PROTOCOL}://{HOST:PORT}/html-pdf-service/service/template/html/body. In this case, the request body can contain a json object with html, css, json fields, where css and json fields are optional, e.g., {"html": "< h1 >This is a title</ h1 > < p >This is body</ p >", "css": "h1{color:blue;}"} . This only supports POST requests.
• The service can take the parameters as request parameters by calling {PROTOCOL}://{HOST:PORT}/html-pdf-service/service/template/html/params. In this case, the request parameters contain html, css, json fields, where css and json fields are optional, e.g., html="< h1 >This is a title</ h1 > < p >This is body</ p >"&css="h1{color:blue;}" .

This template service always responds with JSON Body which contains a list of formed HTML output.

Management Endpoints

These endpoints are provided by the spring-boot framework.
They are generally available at {PROTOCOL}://{HOST:PORT}/html-pdf-service/

1. <code>/health</code> shows general health of the application
2. <code>/info</code> shows custom service info (Not in use)

Endpoints

Base Application URL: {PROTOCOL}://{HOST:PORT}/html-pdf-service/ e.g., http://localhost:8080/html-pdf-service
Base Service URL: {PROTOCOL}://{HOST:PORT}/html-pdf-service/ e.g., http://localhost:8080/html-pdf-service/service/convert/html or http://localhost:8080/html-pdf-service/service/template/html

The service endpoints get appended to the base service endpoint url, e.g., http://localhost:8080/html-pdf-service/service/convert/html/params or http://localhost:8080/html-pdf-service/service/template/html/params.

1. /params takes request parameters and responds with the file in the HTTP Servlet Response.
2. /params/byte takes request parameters and will return a byte array of the generated PDF file.
3. /body takes request body as json and responds with the file in the HTTP Servlet Response.
4. /body/byte takes request body as json and will return a byte array of the generated PDF file.

USAGE & EXAMPLES

Printing Single Letter With Simple JSON

HTML

<h1>HELLO </h1> <p>{name.first} </p> <p>{name.second} </p>

JSON

{ "name": { "first": "Farrukh", "second": "Mirza" } }

Printing Multiple Letters With Simple JSON ARRAY

HTML

<h1>HELLO </h1> <p>{name.first} </p> <p>{name.second} </p>

JSON

[ { "name": { "first": "Farrukh", "second": "Mirza" } }, { "name": { "first": "Jack", "second": "Bauer" } } ]

Printing Single Letter With JSON Containing Repeated Data

In order to print, e.g., multiple rows in a table, use the <repeat> tag. The elements in the array can be referenced using [*] notation.

HTML

<h1>HELLO </h1> <table> <repeat> <tr> <td>{names[*].first} </td> <td>{names[*].second} </td> <tr> </repeat> </table>

JSON

{ "names": [ { "first": "Farrukh", "second": "Mirza" }, { "first": "Jack", "second": "Bauer" } ] }

Printing Multiple Letters With JSON ARRAY Containing Repeated Data

In order to print, e.g., multiple rows in a table, use the <repeat> tag. The elements in the array can be referenced using [*] notation.

In this case multiple PDFs will be generated. Each PDF can be unique in this case, as the repeated data can vary per json object in the array.

HTML

<h1>HELLO </h1> <table> <repeat> <tr> <td>{names[*].first} </td> <td>{names[*].second} </td> <tr> </repeat> </table>

JSON

[ { "names": [ { "first": "Farrukh", "second": "Mirza" }, { "first": "Jack", "second": "Bauer" } ] }, { "names": [ { "first": "Ethan", "second": "Hunt" }, { "first": "Michael", "second": "Corleone" }, { "first": "Json", "second": "Bourne" } ] } ]

NOTES

1. FlyingSaucer is able to pull images and place into PDF, however, the image url must be publicly accessible.

TESTED

Application Servers

This service is tested on the following application servers:

1. Apache Tomcat version 8.0.28
2. WildFly 10.0.0.Final
3. Standalone deployment (Embedded Tomcat)

Web Browsers

This service is tested on the following web browsers:

1. FireFox 47.0
2. Google Chrome Version 51.0.2704.106 m
3. Internet Explorer 11