How eclipse imports the jar package BUILD PATH

As shown, the contents of the red box do not exist in the directory, why?

To summarize: The JRE System Library and Maven dependencies is not a normal folder, it is libraries, it is putare the jar packages and engineering in the Jdk\jre\lib, respectively .automatically downloaded from the remote repository depending on thethe jar package, as shown in:
Similar eclipse default comes with the libraries, and there are several:
How do I create a libraries? In the Package Explorer view, right-click the project, clicking Build Path, click Configure Bulid Path, and click Libraries, as shown in:
Explain the following

Add JARs = Add in-Project package

Add E= Add package outside the project

ADD Li brary = Add a library

Add Class folder = Add a class

How to add a jar:

 way one: Add jar package directly   

you can directly click on the " ADD E  JARs", open the interface as shown below, you can select the jar package you want to introduce, in the popup interface, select the Jar package, click" Open ", as shown, we will see the introduction of the jar package, can directly see, and not in libraries. 

Then click "OK", you will find that the project will be one more library, called referenced Libraries, as shown:

Method Two: Add the library first, and then add the jar package to the library:

Click on the Add Library ..., pop up the interface as shown below, select User Library:

In the interface shown below, enter the name of the library to be created and click "OK" to create the success.

Once created, double-click the library you just created, as shown in:

You can add the required jar package to the library by clicking on "User Libraries", selecting "Spring Framework Libraries", and then clicking "Add External JARS ..." Pop up the interface shown below. As shown in the following:

How eclipse imports the jar package BUILD PATH