Correctly distinguish the similarities and differences among API, rest API, restful API and web service

notice API What do you think of ？ It's the interface 、 Third party call 、 still API file ？ At first glance, you may think this is too familiar , Isn't this a daily series of system development ？ But think about it , You'll find that API The concept of is so vague in your mind . How do you search through search engines API, You will see information like this ：API——Application Programming Interface( Application programming interface ), This is too abstract . Next , I will combine some experience I have summarized in the development , Talk in a popular way API、REST API、RESTful API as well as Web Service The connection and difference between these four .

1、API And REST API

What is? API? Here is the definition given by Wikipedia ： Application program interface （ English ：Application Programming Interface, abbreviation ：API; Also known as application programming interface ） It is an agreement on the connection of different components of the software system . This pair API The definition of is too broad and abstract , And in general ,API It is the interaction between one application and another application “ communication ” The way （ agreement ）. stay Web Application development ,API It is a main way of data retrieval through the network ,API The document will inform you of the URL list 、 Query parameters 、 Request mode and response status , Its purpose is to reduce Web Difficulty of application development , Share data between two applications （ Text 、 Audio 、 video 、 Pictures, etc ）, And shield its internal complex implementation details .

REST yes Representational State Transfer Abbreviation , The literal translation is ： State the transition .REST API It's a group about how to build Web Applications API Architecture rules for 、 Standards or guidelines , Or say REST API It's following API An architectural style of principles .REST It's specifically for Web Designed for application , The goal is to reduce the complexity of development , Improve the scalability of the system . Here is the design REST Some basic conditions and principles that need to be met or followed when designing a style system architecture ：

• 1、 stay REST Architecture ,Web Everything in （ Text 、 Audio 、 video 、 picture 、 link ） Can be uniformly abstracted as resources （resource）
• 2、 stay REST Architecture , Each resource has its corresponding unique resource identifier （resource identifier）, When the state of a resource changes , The resource identifier will not change
• 3、 stay REST Architecture , All operations are stateless .REST Architecture follows CRUD principle , All resources are available through GET、POST、PUT and DELETE These four behaviors complete the corresponding operations .
• 4、 Caching （ optional ）, stay REST Caching is needed in the architecture to effectively handle large numbers of requests
• 5、 Interface consistency

Now? , I understand API and REST API Basic concepts of , What are the similarities and differences between the two ？ If we explain it according to the concept of set in Mathematics API And REST API The connection and difference between ,API yes REST API Superset ,REST API yes API Subset ; be-all REST API All are API, But not all API All are REST API. A more popular explanation is ： All men are human , But not everyone is a man .

2、REST API And RESTful API

In the first section , I learned what is REST API, Let's talk about REST API And RESTful API The similarities and differences between . Many beginners can easily equate the two , Think RESTful API Namely REST API, This may be simply understood literally , When you deeply understand the essence of both , You will find that it is not .REST API yes Web API A specification or guiding principle of design , and RESTful API It is a specific implementation of the architecture design principles or specifications . in other words ,RESTful API yes REST API Informal implementation of , Because of the realization of REST API There are many ways ,RESTful API It's just one of them , And not completely satisfied REST API All design principles of , Every developer is implementing REST The emphasis of architecture will be different .

Many beginners are easy to learn REST API And RESTful API The two concepts are confused , I think it's just literally , Without paying attention to their own meaning （ Just like knowing Chinese characters , Read while , Boundless reading in the middle , Taken out of context ）. This is like many people will equate transgender people with women , Transgender people may have facial features that look like women , But transgender people are infertile , It just meets most of the conditions that define a woman （ Realization ）, But not women in essence .

Next , Through a simple example to deepen the understanding of REST API and RESTful API The understanding of the . An implementation is given below CURD Operation of the RESTful API Design case ：

explain ：resource Refers to the name of a resource , When you can student( Student )、teacher( teacher )、book( Books ) wait , Nouns are usually used to express ;{id} It refers to the unique identifier of a resource （resource identifier）

Here is a specific example , Take student management as an example , Design student management API. Student resources include ID, Name and course information , Student resource information is as follows ：

Now? , We need to save student data to database , Then execute the query 、 Operation of modifying and deleting student data . Student management API Called by the user of API as follows ：

• 1、 Create student resources ：[POST] http://www.example.com/student
• 2、 Get all student resources ：[GET] http://www.example.com/students
• 3、 obtain ID=1001 Student resources ：[GET] http://www.example.com/student/1001
• 4、 modify ID=1001 Student resources ：[PUT] http://www.example.com/student/1001
• 5、 Delete ID=1001 Student resources ：[DELETE] http://www.example.com/student/1001

The previous content says ,API Sharing data resources , And shielding the internal implementation ,API Users of （ client ） Focus on resources （ Read the data ）, You don't need to know API Internal construction ;API The provider of （ Server side ） Only focus on your own internal implementation , It doesn't matter API Users （ client ） The state of . In order to deepen the understanding of this concept , Student management is given below API Internal implementation example of ：

explain ： The sample code is based on Spring MVC Implemented .

In addition to the above , You can also filter the query data by providing key value pairs , For example, when obtaining all student data , Just want to get the data of female students , It can be done in this way ：

[GET] http://www.example.com/students?gender=female

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Tip： If API It has the function of data filtering , Corresponding to the server API The implementation code also needs to be adjusted .

In the previous content , We mentioned RESTful API yes REST API Informal implementation or specification of . Why do you say that ？ Because in RESTful API In the design of , We can go through GET By CURD operation , It can also be done through DELETE Behavior to create resources , adopt POST Behavior to modify resources , Its implementation method is not rigorous or not strictly in accordance with REST API Proposed constraints . So RESTful API yes REST API Informal implementation of .

3、REST And Web Service

3-1、 What is? Web Service?

Such as the World Wide Web Consortium （W3C） Described ,Web Service It is available on various platforms and / Or the standard method of interoperability between different software applications running on the framework .Web Service Is characterized by good interoperability and scalability , And due to the use XML It can describe the process of program processing . They can combine different services in a loosely coupled manner to achieve complex operations . Programs that provide simple services can interact with each other , To provide complex value-added services .

Two Web Service It's mainly through HTTP Network protocol for communication , As we know SOA( Service oriented architecture ), Mainly depends on XML-RPC and SOAP(Simple Object Access Protocol, Simple object access protocol ).

Tip： Never put SOA（ Service Oriented Architecture ） and SOAP( Simple object access protocol ) Mix up , The former is a form of architecture design , The latter is a data exchange protocol .

A simple example ： Suppose a Web Service A Provide to allow other applications to pass URL Access to user information ：[GET] http://www.abc.com/{id}.id Is the unique identifier of the user , Request this URL User information will be obtained . Now suppose the browser 、 mobile phone 、 Users of desktop applications need access to services A User information provided , These three only need to request services A Provided URL Address , And enter the user id Information is enough . As for the implementation of the three different clients （ programing language ） What and service A It doesn't matter , As long as the service can be parsed A Back to XML Just documents . such , The exchange of data between applications can be independent of the specific language and environment . This is like people in different countries and languages , As long as you can know the grammatical structure of the other language , Two people can communicate .

3-2、Web Service The advantages of

Use Web Service It has the following advantages ：

• 1、 Interoperability ：Web Service Allow communication between applications , Exchange data and share services .
• 2、 Usability ：Web Service The function of can be found from simple information to complex algorithm calculation .
• 3、 Reusability ：Web Service They can be combined with each other , To provide more complex services , Because of its interoperability , It can be easily reused in other services Web Service Components , Improve the reuse rate of services .
• 4、 Easy to deploy ：Web Service Can be deployed based on Internet The standard Containers in , Such as Apache、Axis2 etc. , In order to provide HTTP perhaps WSDL（ Web service definition language ） Driven services .
• 5、 The cost is low ：Web Service It is packaged into Web Deploy service components , Thus reducing the cost of use .

3-3、Web Service The type of

at present ,Web Service There are two main schools ：

• 1、 be based on SOAP Of Web Service : SOAP( Simple object access protocol ) It's based on XML The agreement , To visit Web Service. Its interface is described in a machine processable format , be called WSDL(Web Service definition language ) file . By using standard XML Document to describe Web Service, stay XML In file , The interface information will be recorded in detail , Such as message format 、 Transmission protocol, location of interaction and other information .
• 2、 be based on REST Of Web Service ：REST(Representational State Transfer) It's a software architecture , It USES JSON To describe the data format , most important of all HTTP Transmission protocol pair REST It is not necessary .

3-4、REST And SOAP The difference and connection

below , Use a table to compare REST And SOAP The similarities and differences between ：

summary

As mentioned above , We know what is API, What is? REST API, What is? RESTful API as well as Web Service Related concepts of .API Represents the application programming interface , It is a relatively broad definition or an agreement , It exists as an interface for software programs to communicate with each other .REST API yes API A subset of , be-all REST API All are API;RESTful API It's right REST API An informal implementation of architectural style .API And Web Service Both are means of communication between service providers and service consumers . Last , In order to quickly identify API And Web Service Differences between , The differences between these two methods are sorted into a comparison table as follows ：