I'm trying to learn some basics of Java and Spring. Recently I came across some beginner project and one of the first steps was to create a Spring Initializr thanks to its website, where everything is clear to me. The next step was to create a basic package structure in the project: model, controller, repository, config, service.

Could someone explain me what exactly is meant by creating these packages after creating a new project? I tried to look up the information myself, but unfortunately I couldn't find an answer anywhere.

CodePudding user response：

I will start by recommending reading about Packages in Java.

In a nutshell, packages are folders. They are used for storing (mainly) classes, but other entities can be stored in packages as well. For example, text files, pictures, etc. In Java, there is no hard set rule that state that only classes must be stored in packages. That said, this is typically not the way projects are structured.

One of the most important functions of packages is to provide namespace for classes. Consider two classes named Table. One is a table containing data and the other is a table used to put stuff on top of; for example a dining table. This means that Table will have to different meanings. Operating Systems will not allow for two files with the same name to exist in the same folder. Therefore, you need to put them in two folders (packages). In the code, you can break ambiguity by declaring the objects using the class' fully-qualified name. For example,

myproject.furniture.Table diningTable = new myproject.furniture.Table();
myproject.data.Table dataTable = new myproject.data.Table dataTable();

There is also access protection with packages by using default access modifier (no modifier). For example:

package myproject

class PackagePrivateClass {
    // class contents omitted
}

Notice that this class is not public. In Java, this means that this class is visible to other classes in the same package only. Not even classes in sub-packages will have access.

In summary, packages provide namespace, physical organization, and access protection.

The second thing you should be familiarized with is the best practices with regards to naming your packages. Organizations tend to have packages structured with the domain first, then the main system the code is part of, then subsystems, etc. Before providing examples, here is an article about Package Naming from Oracle.

• java.awt => Contains all of the classes for creating user interfaces and for painting graphics and images. AWT stands for Abstract Window Toolkit

When you see the package name, it gives developers and idea what type of classes can be found inside. This will help looking for functions when you are not familiarized with the API (which in turn will help you learning the API much faster). Imagine how hard would be to learn Java if all classes were in the same folder. Imagine how hard will be to figure out what the project does if meaningful names are not used. In the example above, it is kind of easy to figure how what to expect out of classes in the java.awt package.

I was hoping to give you more examples, but I am out of time. Maybe later I will return and write more about this.

CodePudding user response：

There is no specific layout or code structure for Spring Boot Projects. However, there are some best practices followed by developers that will help us too. You can divide your project into layers like service layer, entity layer, and repository layer.

1. We use the entity layer to write all model and POJO classes. We annotate them with @Entity.

2. We use @Repository to indicate that this is a repository interface that is used to do some basic CRUD operations. Sidenote:- You don't have to write @Repository for classes that implement or interfaces that extends Repository interfaces provided by Spring Boot framework.

3. We use @Service to say that this is the service class where your all business logic will be present.

4. We use the controller layer to receive HTTP requests and send back HTTP Responses or views.

You can learn and understand more from here

You can refer to this Image to understand the structure project structure

CodePudding user response：

Package is nothing but a group of classes. You want to categorize your classes basis their respective purposes. If it's just for self-learning, your package structure should be like

org.novak.sample.service.*

This package should contain all Services, not anything else.