JUnit is a Java library for testing Java Code. To use this library you have to annotate the method which should be called during a test with "@Test". After this you can call code from you application within this test method. And always if you go on your project and click on "Run as JUnit test" the annotated methods will be invoked. Usually in the test methods you call some Code from the business logic and after this you can test for example with the JUnit function "assertEquals()" the result. Is the result right or wrong it will be displayed at the end of the Junit test
The assert functionality is also in the Java native code. But most of all programmers uses the JUnit library for testing Java code.Here you can download JUnit with dependencies
I use the Jackson library for parsing and writing JSONs. For this I create a plain old Java Object and after this I will call "readValue([json], Person.class)". In my opinion this is very comfortable. You can say now you need to create a plain old Java Object and this is very much effort. But in my software architectures is such a object always needed. And because of this it is no additional effort for me.
The writing to JSON works in the same way. You have to call the method "writeValue([jsonFile], personObj)". and passing a object to it. After this the JSON representation of this object will be written to the file.Please download this file for Jackson with dependencies
Spring is not only one library for one situation. You can use spring for different use cases. For example Spring offers a security mechanism for implementing a user management. Furthermore it is possible to use Spring Data together with a Java Persistence API. Then it is possible to make very easy Data Access Objects. For this you have to create only an interface which contains methods with a certain convention. When you now call these methods you will get all the data you want. Spring makes the implementation for you.
There are so much functionalities which will be provided by spring. It is impossible to write everything of them without creating a whole book. For example there is also a mechanism to read an write properties from a properties file in a very comfortable way.Here is the download for Spring with dependencies
Hibernate is a Object-Relational Mapping library. You can annotate you Java objects with annotation which will provided by JPA specification and after this hibernate can create a database table for you. For reading from this database table you make no SQL statements. You will fetch the data via the hibernate objects. This is very comfortable and is in my opinion much faster than SQL statements. Switching between databases is also very easy. You have the change a value in the configuration and after this the database is switched.At this site you can download hibernate with dependencies