Create jar using gradle and setting Main class

Our build script must create an executable jar file. In other words, we must be able to run our program by using the command:

java -jar jarfile.jar

Let’s find out how we can fulfil this requirement.

Creating a Java Project

We can create a Java project by applying the Java plugin. We can do this by adding the following line to our build.gradle file:

1	apply plugin: 'java'

The Project Layout of a Java Project

The default project layout of a Java project is following:

• The src/main/java directory contains the source code of our project.
• The src/main/resources directory contains the resources (such as properties files) of our project.
• The src/test/java directory contains the test classes.
• The src/test/resources directory contains the test resources.

All output files of our build are created under the build directory. This directory contains the following subdirectories which are relevant to this blog post (there are other subdirectories too, but we will talk about them in the future):

• The classes directory contains the compiled .class files.
• The libs directory contains the jar or war files created by the build.

Let’s move on and add a simple main class to our project.

Adding a Main Class to Our Build

Let’s create a simple main class which prints the words: “Hello World” to System.out. The source code of the HelloWorld class looks as follows:

1 2 3 4 5 6 7 8

package hello; public class HelloWorld {     public static void main(String[] args) {         System.out.println("Hello World!");     } }

The Tasks of a Java Project

The Java plugin adds many tasks to our build but the tasks which are relevant for this blog post are:

• The assemble task compiles the source code of our application and packages it to a jar file. This task doesn’t run the unit tests.
• The build task performs a full build of the project.
• The clean task deletes the build directory.
• The compileJava task compiles the source code of our application.

We can also get the full list of runnable tasks and their description by running the following command at the command prompt:

gradle tasks > gradle build The assemble task runs only the tasks which are required to package our application. The build task runs the tasks which are required to package our application AND runs automated tests. We can now try to run our application by using the following command: java -jar first-java-project.jar When we do this, we see the following output: > java -jar first-java.project.jar No main manifest attribute, in first-java-project.jar The problem is that we haven’t configured the main class of the jar file in the manifest file. Let’s find out how we can fix this problem. Configuring the Main Class of a Jar File The Java plugin adds a jar task to our project, and every jar object has a manifest property which is an instance of Manifest. We can configure the main class of the created jar file by using the attributes() method of the Manifestinterface. In other words, we can specify the attributes added to the manifest file by using a map which contains key-value pairs. We can set the entry point of our application by setting the value of the Main-Class attribute. After we have made the required changes to the build.gradle file, its source code looks as follows (the relevant part is highlighted): 1 2 3 4 5 6 7 apply plugin: 'java' jar {     manifest {         attributes 'Main-Class': 'net.petrikainulainen.gradle.HelloWorld'     } }

> java -jar first-java-project.jar

Hello World!










You can see the below addition to Manifest file




Manifest.MF




Manifest-Version: 1.0 Main-Class: hello.HelloWorld







Create Simple application with Nodejs using npm

Below are the summary of the steps I did to create a simple application using nodejs. I have used npm package manager to create this.

Needed Software
1. Download visual studio. get the zip from https://code.visualstudio.com/docs/?dv=winzip
2. Download Nodejs    64 bit binary zip https://nodejs.org/en/download/

Start your first application with Nodejs
1. Create a folder "TuteDemo"
2. Install JSPM and http-server
 a) npm install -g jspm http-server

     This will install jspm and http-server (-g)globally, across server anybody can use it. http-server is very light weight.
  If you have any issues encounter while setting up eg: rename error with path , copy the files to root directory (c:\).
  This will make foder path little less in length.
 
  you will get below output.
---------------------------------
 
C:\Code\React\TuteDemo>npm install -g jspm http-server
C:\node-v8.12.0-win-x64\hs -> C:\node-v8.12.0-win-x64\node_modules\http-server\bin\http-server
C:\node-v8.12.0-win-x64\http-server -> C:\node-v8.12.0-win-x64\node_modules\http-server\bin\http-server
C:\node-v8.12.0-win-x64\jspm -> C:\node-v8.12.0-win-x64\node_modules\jspm\jspm.js
+ http-server@0.11.1
+ jspm@0.16.53
added 341 packages from 233 contributors in 69.733s



2. Initialze the application
 b) nmp init
 press enter and will take default values.
 This will create 'package.json' file with all the initial information related to project.
 Note , root folder name "TuteDemo" automatically taken as package name with lower case.
 Others are set default values and save in json format.


Folder structure

TuteDemo
  -- package.json


{
  "name": "tutedemo",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "",
  "license": "ISC"
}

Below is the output
------------------------

C:\Code\React\TuteDemo>npm init
This utility will walk you through creating a package.json file.
It only covers the most common items, and tries to guess sensible defaults.
See `npm help json` for definitive documentation on these fields
and exactly what they do.



3. Install jspm locally.
  for debugging purposes and our ease of use, we install jspm locally.

 c) npm install jspm --save
  
 this will install and --save for run time depnedency. --save-dev  for build

This will add "node_modules" folder and "package-lock.json" under root folder "TuteDemo" 
update "package.json"

"dependencies": {
    "jspm": "^0.16.53"
  }


Folder structure

TuteDemo
  -- node_modules   --> include all files with /bin folder
  -- package.json
  -- package-lock.json

 output - forgot to add --save at first run
 -----------------------------------------------

C:\Code\React\TuteDemo>npm install jspm
npm notice created a lockfile as package-lock.json. You should commit this file.
npm WARN tutedemo@1.0.0 No description
npm WARN tutedemo@1.0.0 No repository field.
+ jspm@0.16.53
added 316 packages from 212 contributors and audited 2285 packages in 46.101s
found 1 critical severity vulnerability
  run `npm audit fix` to fix them, or `npm audit` for details

C:\Code\React\TuteDemo>npm install jspm --save
npm WARN tutedemo@1.0.0 No description
npm WARN tutedemo@1.0.0 No repository field.



4. Configure github with jspm registry.

 you need to have github account before running this step. Please go to https://github.com/ and make an account if yo do not have, else check your credential and confirm your username and password are working fine.
 just run "jspm" in command prompt, you will get the all the options associated with it.
 Just press enter and will take default values, only babel need to be set for ES6 Transpiler.
 This will create "config.js" and update "package.json"
 I have got few errors in gitgub account verification. However i have included the output as it is.

 with error in github token config.js as follows

 System.config({
  baseURL: "/",
  defaultJSExtensions: true,
  transpiler: "babel",
  paths: {}
});

 "package.json" you will see below

 "jspm": {
    "dependencies": {}
  }

 d) jspm  registry config github

 output
 ------
 C:\Code\React\TuteDemo>jspm  registry config GitHub

Would you like to set up your GitHub credentials? [yes]:yes
     If using two-factor authentication or to avoid using your password you can generate an access token at https://github.com/settings/tokens. Ensure it has public_repo scope access.
Enter your GitHub username:vrtugit
Enter your GitHub password or access token:
Would you like to test these credentials? [yes]:yes
err  Error: self signed certificate in certificate chain
         at TLSSocket. (_tls_wrap.js:1116:38)
         at emitNone (events.js:106:13)
         at TLSSocket.emit (events.js:208:7)
         at TLSSocket._finishInit (_tls_wrap.js:643:8)
         at TLSWrap.ssl.onhandshakedone (_tls_wrap.js:473:38)
Would you like to try new credentials? [yes]:yes
     If using two-factor authentication or to avoid using your password you can generate an access token at https://github.com/settings/tokens. Ensure it has public_repo scope access.
Enter your GitHub username:vrtugit
Enter your GitHub password or access token:
Would you like to test these credentials? [yes]:no
ok   Registry github configured successfully.


Second time

C:\Code\React\TuteDemo>jspm init

Would you like jspm to prefix the jspm package.json properties under jspm? [yes]:yes

Enter server baseURL (public folder path) [./]:
Enter jspm packages folder [.\jspm_packages]:
Enter config file path [.\config.js]:
Configuration file config.js doesn't exist, create it? [yes]:
Enter client baseURL (public folder URL) [/]:
Do you wish to use a transpiler? [yes]:
Which ES6 transpiler would you like to use, Babel, TypeScript or Traceur? [babel]:babel
ok   Verified package.json at package.json
     Verified config file at config.js
     Looking up loader files...
warn Error on lookup for github:systemjs/systemjs, retrying (1).
     Error: fatal: unable to access 'systemjs/systemjs.git/': SSL certificate problem: self signed certificate in certificate chain

warn Error on lookup for github:systemjs/systemjs, retrying (2).
     Error: fatal: unable to access 'systemjs/systemjs.git/': SSL certificate problem: self signed certificate in certificate chain

warn Error on lookup for github:systemjs/systemjs, retrying (3).
     Error: fatal: unable to access 'systemjs/systemjs.git/': SSL certificate problem: self signed certificate in certificate chain

warn Error on lookup for github:systemjs/systemjs
     Error: fatal: unable to access 'systemjs/systemjs.git/': SSL certificate problem: self signed certificate in certificate chain

err
err  Error downloading loader files.
err

GIT ssl error

I got an ssl error executing git commands.

eg:

$ git push origin master
fatal: unable to access 'https://github.com/vrtugit/git-github.git/': SSL certificate problem: self signed certificate in certificate chain

Solution ( Workaround)

switch off ssl verification

 git -c http.sslVerify=false push origin master

https://stackoverflow.com/questions/11621768/how-can-i-make-git-accept-a-self-signed-certificate