spring boot

Spring Data error: getOutputStream() has already been called for this response

Spring data with spring boot error when using mapping

Spring boot has made life of the java developers a bliss. Thanks a million for the dedicated guys in spring.

Saying that, if you are working typical database related project with spring boot, you might have some error like this


java.lang.IllegalStateException: getOutputStream() has already been called for this response
at org.apache.catalina.connector.Response.getWriter(Response.java:624) ~[tomcat-embed-core-8.5.16.jar!/:8.5.16]
at org.apache.catalina.connector.ResponseFacade.getWriter(ResponseFacade.java:211) ~[tomcat-embed-core-8.5.16.jar!/:8.5.16]
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facebook social marketing

Post to Facebook From app – Using PHP

Post to Facebook programatically

You can post whatever you like from PHP to your or company’s page. Facebook has provided an SDK that makes life easier to post to the Facebook page.

This is ideal if you want to post to facebook, from cron job especially. Or on some event like right after the post in wordpress.

First thing first, you need to have a developer account on Facebook and you can do that easily and free on https://developers.facebook.com

Then you need to create an app. A single page or something like that would work. You will see how to create one when you are setting up your account for developer.

Once you have that, on the left menu, you will see dashboard. This contains important information about the app you will use to interact from your code.
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String Ordered Permutation Algorithm Problem

String Permutation Problem

The algorithm problem goes something like this:

If you are given a character and its possible substitution set, then write a function that would print all the permutation of its characters.

Eg.

Given word “java”

Substitution Set =>
j [“J”, “7”]
a [“@”, “J”, “9”]
v [“V”, “^”]

Based on this, the possible permutations could be: J@V@, 7JV9..

Here is my approach using java
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setting JAVA_HOME on mac osx

How to set JAVA_HOME ON MAC OSX computer

Setting java_home as environment variable might be almost required especially when you use frameworks. Frameworks like axis2 web server and others. Also some code editors require that too.

What is environment variable

Those are variables that would allow you to execute command line actions from any directory, basically from everywhere.

The simplest example is using java -version. In this case, if you don’t have explicit environment variable on where to look for, it requires you to either be in the java folder or to fully list the whole path till bin folder.

Setting JAVA_HOME in mac osx

The first part is to make sure you have java installed in your machine.

java -version

If this is giving you an output with the version, then it means java is installed, otherwise, you should first install it.

The following task will be to find out where the binary files are located.

Click the apple icon on the left top corner of your mac and select system preferences..

system preference

system preference

And from there click Java and you will get the path information from there.

Once you got where the java is located, usually on /Library/Java/JavaVirtualMachines/jdk1.***/Contents/Home

Open the bash properties file


vi ~/.bash_profile

And add the java path here

export JAVA_HOME=export JAVA_HOME=/Library/Java/JavaVirtualMachines/jdk1.8.0_91.jdk/Contents/Home

The above would be what it would look like fro jkd 1.8 on my El Capitan macbook pro.

react-native application has not been registered

react-native application has not been registered command error

Playing with react for the mobile development and getting this error?

There are a number of reasons for this to happen.

the name of the react-native class is not matching

Give attention to the line you have something like this

AppRegistry.registerComponent('YOUR-COMPONENT', () => YOUR-COMPONENT);

The name of the component you will be referring as ‘YOUR-COMPONENT’ should align with the main class you refer.

Other instance of node or the react-native app might be running

If other instance of the node process is running make sure to kill it and have clear for the current application you are working on.


ps aux | grep react-native 

Kill the processes that you see on the ps and start the application again.

To kill the process just use kill
Then do the react-native run-ios

hello world weblogic – hello world tutorial on weblogic

hello world weblogic app server

There are lots of application servers for java and oracle weblogic is one of them. As of this writing the current and latest weblogic server is 12c

I will show a simple hello world tutorial on weblogic. The tutorial is for beginners of weblogic server.

This hello world weblogic tutorial assumes you have java skill already.

Installing weblogic server

First thing first, lets install and configure weblogic server
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Simple Servlet example without eclipse

Simple servlet example – how to create servlet without eclipse

These days we are all surrounded by heavy frameworks that make life easier for us. Like maven, spring and hibernate and more. But how can we create a simple servlet website without the need of all those.

The main idea of servlet lies around very simple and intuitive files and structures. Knowing those only is good enough to built a good web app and that is what I will be showing here.

The main parts of the java web app are the following.

1. The Servlet – the java class that is handling the POST and GET http verbs
2. the deployment descriptor – web.xml. File telling how the webapp should be interacted like the url pattern
3. Servlet jar file – This is the jar handling the magic of interaction with the web for the servlet.

Structure of the webapp

Consuming SOAP tutorial – Using java eclipse

Consuming SOAP tutorial from java step by step

SOAP, Simple Object Access Protocol, is older and still usable protocol for exchanging messages between systems.

Since soap is xml based, it is language and operating system independent. You can publish a soap service through your wsdl using Java on Linux and you can consume it through PHP application running on windows.

These days, SOAP is a bit lagging behind RESTful services which are rather more of architectural approaches than being protocol by themselves.

This is a tutorial showing how to consume an existing SOAP service using java language.

For this example, I will use a WSDL published on http://www.webservicex.com/globalweather.asmx?WSDL

In this one, I use already established wsdl for weather related tasks.

Eclipse has a nice tool to make life easier to consume SOAP related messages and I will show you here step by step.

Consuming SOAP tutorial step by step

1. Go ahead and create a new dynamic java project on your Eclipse

dynamic java project

java project

dynamic web project

dynamic web project


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sftp connection

connect to sftp from php

connecting sftp using php

What is SFTP
When to use SFTP
Automating SFTP
What to consider when automating
SFTP download using php code
SFTP upload using php code
List all files on SFTP Server

What is SFTP

SFTP, Secure File Transfer Protocol, is more applicable these days where cyber security is at its peak. Whenever possible, one has to use SFTP as the communications are encrypted.

Most of tools that are used for FTP like filezilla allows using SFTP with minor adjustment. SFTP has to be supported by the server that is providing the FTP server and usually uses different port than that of the FTP.

SFTP is pretty much like FTP as far the connection and usage is concerned. It has just another layer of security to make it more secure while uploading and downloading the file.

Basic server address, username, password and port are still necessary to connect and interact with SFTP server.
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