[How can I get access to output_format column of JIReportJobOutputFormat using jasper api's?]

You will find what you need there : 

http://community.jaspersoft.com/documentation/tibco-jasperreports-server-web-services-guide/v62/v2jobs-service

[Need Help on String to Date Conversion]

As well if SQL you can convert from the query + you have the choice with Java current casting methodology or using the JasperReports built-in functions for Date & Time in the expression Editor.

[Jaspersoft Webservice API support]

You can setup Oauth authentication from JasperReport Server side : 
http://community.jaspersoft.com/wiki/configuring-oauth-20-tibco-jasperreports-server-v61

Then depending on the way you embed JRS using APIs you will always find a way to use it.

[jasperserver not running after installing Webservice Data Source extension]

community version?

[How to use the JasperServer Java Rest Client]

You are not obliged to use a configuration file. 
But if you wish to , in your code you will need to use : 

https://github.com/Jaspersoft/jrs-rest-java-client#loading-configuration-from-file

Or a manual way :

https://github.com/Jaspersoft/jrs-rest-java-client#creation-of-manual-configuration

It is pretty well explain in the readme of the github project...

[jasperserver not running after installing Webservice Data Source extension]

What version of jasperreports server are you using ?

[Help with Jasper 6 on Tomcat 7 Ubuntu 14.04]

It is in the documentation, when you use the package manager to install Tomcat you need to define in the default_master.properties file of the buildomatic the following : 
 

# Tomcat app server root dir
# appServerDir = C:\Program Files\Apache Software Foundation\Tomcat 7.0
# appServerDir = /home/devuser/apache-tomcat-7.0.26
# if linux package managed tomcat instance, set two properties below
CATALINA_HOME = /usr/share/tomcat6
CATALINA_BASE = /var/lib/tomcat6

[How to use parameters in query of ElasticSearch data adapter]

yes but I dont think you need the double quotes around the $P

[Jasper Studio (Web Service Adapter) giving null response - Rest Api]

Do you have the same Headers as POSTMAN ? URL properties as well?
Did you configure the kind of request properly (POST, GET) ? 

Authentication as well?

[Custom DataSource backed by REST API]

Can you explain clearly what is the use case you want to setup !?

[Im trying to display a collumn on my reports based on the input controls selected.]

Try to use the "Print When Expression" properties of the reports components to display/hide them regarding conditions ie. parameters values .

[Unable to build HTML5 pie chart with data set]

You should find a way to pivot your data to get something like : 

Categorie;Value

A;123

B;234

If using SQL , a CASE WHEN will do the Job.

[Nested JSON fields]

Add "technical_specifications" as root node.
Then inside nodes as fields.

[What is the best way to implement REST for creating Reports.]

If you want to use REST as a datasource : 

http://community.jaspersoft.com/project/web-service-data-source

[Get data from external REST and process data]

You can use this plugin : 
http://community.jaspersoft.com/project/web-service-data-source

If you need to process modification to data just use variables.

[Anybody knows how to retrieve subreport value without displaying subreport?]

Why dont you create a variable and return it. 
Pay attention : 

• Try to set the calculation type as System in the main report mapped variable.
• If the variable is received from the subreport in one band, it can be used in the main report in the next band only

  

[Conditional Scheduling of jobs in jasperserver-5.6.1]

Or you can use these components : 

http://community.jaspersoft.com/project/jaspersoft-etl-plugin

[Is there a way to set the active theme via a RESTful API call?]

even you are using organization_1 by default.

[Is it there a way to make a report consume a REST webservice as a DataSource?]

You can find what you need there : 

http://community.jaspersoft.com/project/web-service-data-source

[Running report via web services with parameters]

Can you display an example of REST request ?

[Java Rest_v2 execution Report doesn't produce the pdf file]

You should use the java rest client which would make your life easier : 

https://github.com/Jaspersoft/jrs-rest-java-client

[Removing all "decorations" for a dashboard or report]

You can find information about visualize.js there : 

http://community.jaspersoft.com/documentation/tibco-jasperreports-server-visualizejs-guide/v62/api-reference-visualizejs

[How to divide data column wise]

Has your query just one field?

What is your Database? Some of them have some PIVOT features.

 

[How to add a hyperlink to another report and to work on PDF or Excel export]

Have a try using a reference hyperlink instead of Report Execution.

[Access Denied for custom new roles created.]

Do these user have the ROLE_USER as well? This Role is with defautlt configuration mandatory.

As well are you working in multi-tenancy mode ? If yes are you sure you created the ROLE at the good level ie. for the good organization or  Root level?
Regarding this for which ROLE (Root or Specific Tenant) did you grant access to those folders?