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Obsidian_Informatik/Semester 2/EIST/EIST CHEATSHEET.md
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List of contents

  1. #REST API with Spring
  2. #Flask API in Python
  3. #DOCKER
  4. #gRPC

REST API in Java with Spring

Making REST API Requests

With WebClient object:

(e.g Spring WebFlux)

GET

public void getAllPersons(CustomerSortingOptions sortingOptions, Consumer<List<Customer>> customerConsumer) {
        webClient.get()
                .uri(uriBuilder -> uriBuilder
                        .path("customers")
                        .queryParam("sortField", sortingOptions.getSortField())
                        .queryParam("sortingOrder", sortingOptions.getSortingOrder())
                        .build())
                .retrieve()
                .bodyToMono(new ParameterizedTypeReference<List<Customer>>() {
                })
                .onErrorStop()
                .subscribe(newPersons -> {
                    customers.clear();
                    customers.addAll(newPersons);
                    customerConsumer.accept(customers);
                });
    }

POST

public void addPerson(Customer customer, Consumer<List<Customer>> customerConsumer) {
	// TODO Part 2: Complete the http post request to the server
	webClient.post()
			.uri("customers")
			.bodyValue(customer)
			.retrieve()
			.bodyToMono(Customer.class)
			.onErrorStop()
			.subscribe(newCustomer -> {
				customers.add(newCustomer);
				customerConsumer.accept(customers);
			});
}

PUT

public void updatePerson(Customer customer, Consumer<List<Customer>> customerConsumer) {
    // TODO Part 2: Complete the http put request to the server
    webClient.put()
            .uri("customers/" + customer.getId())
            .bodyValue(customer)
            .retrieve()
            .bodyToMono(Customer.class)
            .onErrorStop()
            .subscribe(newCustomer -> {
                customers.replaceAll(x -> x.getId().equals(customer.getId()) ? newCustomer : x);
                customerConsumer.accept(customers);
            });
}

DELETE

public void deletePerson(Customer customer, Consumer<List<Customer>> customerConsumer) {
	// TODO Part 2: Make an http delete request to the server
	webClient.delete()
			.uri("customers/" + customer.getId())
			.retrieve()
			.toBodilessEntity()
			.onErrorStop()
			.subscribe(deletedCustomer -> {
				customers.remove(customer);
				customerConsumer.accept(customers);
			});
}

Just in case: webClient Constructor

public CustomerController() {
	this.webClient = WebClient.builder()
			.baseUrl("http://localhost:8080/")
			.defaultHeader(HttpHeaders.ACCEPT, MediaType.APPLICATION_JSON_VALUE)
			.defaultHeader(HttpHeaders.CONTENT_TYPE, MediaType.APPLICATION_JSON_VALUE)
			.build();
	this.customers = new ArrayList<>();
}

With Request Parameters:

Endpoint:

@GetMapping("persons")
public ResponseEntity<List<Person>> getAllPersons(PersonSortingOptions sortingOptions)  { // Don't use @RequestParams unless object is simple(for example String), for more complex objects Spring parses the object by itself
	List<Person> persons = personService.getAllPersons(sortingOptions);
	return ResponseEntity.ok(persons);
}

Request:

public void getAllPersons(PersonSortingOptions sortingOptions, Consumer<List<Person>> personsConsumer) {
		this.webClient.get()
			.uri(uriBuilder -> uriBuilder // Use uriBuilder to build the path
					.path("persons")
					.queryParam("sortingOrder",sortingOptions.getSortingOrder()) // The fields are passed separately
					.queryParam("sortField",sortingOptions.getSortField())       // In the format: ("Name",value)
					.build()
			)
			.retrieve()
			.bodyToMono(new ParameterizedTypeReference<List<Person>>() {
			})
			.onErrorStop()
			.subscribe(persons -> {
				this.persons = persons;
				personsConsumer.accept(this.persons);
			});

}

With RestTemplate:

GetMapping("/getTimeLine/{id}")
public List<Tweet> getTimeLine(@PathVariable("id") int userID) { 
	headers.setContentType(MediaType.APPLICATION_JSON);
	
	ResponseEntity<List<Tweet>> response = restTemplate.exchange(
	getActivityURL + userID, // Set the uri HttpMethod.GET,
	null, // requestEntity = null as there is no body,
	new ParameterizedTypeReference<List<Tweet>>(){} // response body type );
		return response.getBody();
}

REST API Endpoints

Example Java class:

@RestController
@RequestMapping("/activity")
public class ActivityController {
    private Map<Integer, List<Tweet>> userActivityMap = new HashMap<>();
    private Map<Integer, List<User>> userFollowedMap = new HashMap<>();

    @GetMapping("/getActivity/{id}")
    public List<Tweet> getActivity(@PathVariable("id") int userID) {
        List<Tweet> userTweets = userActivityMap.get(userID);

        if(userTweets == null) return new ArrayList<>();

        return userTweets;
    }

    @PostMapping("/addActivity")
    public void addActivity(@RequestBody Tweet tweet) {
        userActivityMap.computeIfAbsent(tweet.getUser().getUserID(), x -> new LinkedList<>());
        userActivityMap.get(tweet.getUser().getUserID()).add(tweet);
    }

    @PostMapping("/addFollower")
    public void addFollower(@RequestBody FollowRequest followRequest) {
        User follower = followRequest.getFollower();
        User followed = followRequest.getFollowed();

        userFollowedMap.computeIfAbsent(follower.getUserID(),x -> new LinkedList<>())
                .add(followed);
    }

    @DeleteMapping("/deleteActivity")
    public void deleteActivity(@RequestBody Tweet tweet) {
        List<Tweet> userTweets = userActivityMap.get(tweet.getUser().getUserID());
        if(userTweets == null) return;

        userTweets.remove(tweet);
    }

    @DeleteMapping("/deleteFollower")
    public void deleteFollower(@RequestBody FollowRequest followRequest) {
        User follower = followRequest.getFollower();
        User followed = followRequest.getFollowed();

        List<User> followedUsers = userFollowedMap.get(follower.getUserID());
        if(followedUsers == null) return;

        followedUsers.remove(followed);
    }

    @GetMapping("/getFollowedList/{id}")
    public List<User> getFollowedList(@PathVariable("id") int userID) {
        // TODO: this method is also not complete, so you have to implement it accordingly :)
        List<User> followed = userFollowedMap.get(userID);
        if(followed == null) return new ArrayList<>();
        return followed;
    }
}

Excersises:

  • L02PE01 TUM Social App
  • L02PE02 REST Architectural Style Part 2
  • L09PE02 Wizardry Character Creation
# Flask API in Python ## *Server side* endpoints

GET

@api.route("/<key>", methods=["GET"])
def get(key: str) -> Response:    
    """
    Retrieve the file-content associated with the given key owned by the user.
    If there is no user-id `uid` given in the request body or the user-id does not match, return error message and status.
    Otherwise, return the file-content and success status.
    """
    request_body: dict = request.json
    ff: FileFolder = current_app.ff # type: ignore
    
    user_id = request_body.get("uid")

    if user_id is None:
        return Response(NO_UID_IN_REQUEST_BODY,BAD_REQUEST)

    file = ff.get(key)

    if file is None:
        return Response(response=KEY_DOES_NOT_EXIST % key, status=NOT_FOUND)
    
    if file.uid != user_id:
        return Response(response=NO_ACCESS_TO_ENTRY % key, status=BAD_REQUEST)

    return Response(response=file.content,status=OK)
    pass

PUT

@api.route("/<key>", methods=["PUT"])
def put(key: str) -> Response:    
    """
    Upsert a file-content associated with the given key owned by the user.
    If there is no user-id `uid` or file-content `content` given in the request body, return error message and status.
    Otherwise, return the success message and success status
    """
    request_body: dict = request.json
    ff: FileFolder = current_app.ff

    if "uid" not in request_body:
        return Response(NO_UID_IN_REQUEST_BODY,BAD_REQUEST)
    if "content" not in request_body:
        return Response(NO_CONTENT_IN_REQUEST_BODY,BAD_REQUEST)

    uid = request_body["uid"]
    file_content = request_body["content"]

    old_entry = ff.get(key)

    if old_entry is None:
        entry = Entry(uid,file_content)
        success = ff.put(key,entry)
        if success:
            return Response(PUT_SUCCESS,OK)
        else:
            return Response(NO_SPACE_IN_FILE_FOLDER,BAD_REQUEST)
        
    
    if uid != old_entry.uid:
        return Response(NO_ACCESS_TO_ENTRY % key,status=BAD_REQUEST)

    entry = Entry(uid,file_content)
    ff.put(key,entry)

    return Response(PUT_SUCCESS,OK)
    pass

DELETE

@api.route("/<key>", methods=["DELETE"])
def remove(key: str) -> Response:
    """
    Remove the file-content associated with the given key owned by the user.
    If there is no user-id `uid` given in the request body or the user-id does not match, return error message and status.
    Otherwise, return the removed file-content and success status
    """
    request_body: dict = request.json
    ff: FileFolder = current_app.ff

    if "uid" not in request_body:
        return Response(NO_UID_IN_REQUEST_BODY,BAD_REQUEST)
    
    uid = request_body["uid"]
    
    entry = ff.get(key)

    if entry is None:
        return Response(KEY_DOES_NOT_EXIST % key,NOT_FOUND)
    if entry.uid != uid:
        return Response(NO_ACCESS_TO_ENTRY % key,BAD_REQUEST)
    
    ff.remove(key)

    return Response(entry.content,OK)
    pass

GET - all

@api.route("/", methods=["GET"])
def list() -> Response:
    """
    List all (key, file-content) tuples owned by the user.
    If there is no user-id `uid` given in the request body, return error message and status.
    Otherwise, return the list of file-content and success status.
    """
    request_body: dict = request.json
    ff: FileFolder = current_app.ff

    if "uid" not in request_body:
        return Response(NO_UID_IN_REQUEST_BODY,BAD_REQUEST)
    
    uid = request_body["uid"]

    items = ff.items()

    output = []

    for key, entry in items:
        output.append(f"{key}:{entry.content}")
    output_string = ".".join(output)

    return Response(output_string,OK)
    pass

Making requests on the client side

Helper method

# make json request to server
def json_request(self, method: str, path: str, body: dict):
	self.conn.request(method, path, json.dumps(body), headers={"Content-Type": "application/json"})
	flask_response = self.conn.getresponse()
	return flask_response.read().decode()

PUT

def put(self, key, content):
	"""
	Upsert (key, content) tuple into the file folder.
	Return the server response
	"""
	request_body = {"uid": self.user_id, "content": content}
	return self.json_request("PUT", f"/{key}",request_body)
	pass

GET

def read(self, key):
	"""
	Retrieve the file-content associated with the given key owned by the user.
	Return the server response
	"""
	request_body = {"uid": self.user_id}
	return self.json_request("GET",f"/{key}",request_body)
	pass

DELETE

def remove(self, key):
	"""
	Remove the file-content associated with the given key owned by the user.
	Return the server response
	"""

	request_body = {"uid": self.user_id}
	return self.json_request("DELETE",f"/{key}",request_body)
	pass

GET - ALL

def list(self):
	"""
	List all file-content owned by the user.
	Return the server response
	"""

	request_body = {"uid": self.user_id}
	return self.json_request("GET","/",request_body)
	pass

Excersises:

  • L03PE01 Online FileFolder

Python - general syntax and tips:

Dictonaries:

thisdict = {  
  "brand": "Ford",  
  "model": "Mustang",  
  "year": 1964  
}  
print(thisdict["brand"])

thisdict = dict(name = "John", age = 36, country = "Norway")  
print(thisdict)

You can check if a key exists with the keyword in:

if "model" in thisdict:  
  print("Yes, 'model' is one of the keys in the thisdict dictionary")

You can loop over keys and values in dictionary:

for x in thisdict: # Loop over keys 
  print(x)
for x in thisdict.keys():  #Another way to loop over keys
  print(x)
  
for x in thisdict:  # Loop over values
  print(thisdict[x])
for x in thisdict.values(): # Another way to loop over values
  print(x)
 
for x, y in thisdict.items():  # Looping over key-value pairs as tuples
  print(x, y)

Dictionary methods

Method Description
clear() Removes all the elements from the dictionary
copy() Returns a copy of the dictionary
fromkeys() Returns a dictionary with the specified keys and value
get() Returns the value of the specified key
items() Returns a list containing a tuple for each key value pair
keys() Returns a list containing the dictionary's keys
pop() Removes the element with the specified key
popitem() Removes the last inserted key-value pair
setdefault() Returns the value of the specified key. If the key does not exist: insert the key, with the specified value
update() Updates the dictionary with the specified key-value pairs
values() Returns a list of all the values in the dictionary

DOCKER

Docker reference: https://docs.docker.com/

Dockerfiles

https://docs.docker.com/get-started/docker-concepts/building-images/writing-a-dockerfile/ https://docs.docker.com/reference/dockerfile/

FROM python:3.13
WORKDIR /usr/local/app

# Install the application dependencies
COPY requirements.txt ./
RUN pip install --no-cache-dir -r requirements.txt

# Copy in the source code
COPY src ./src
EXPOSE 8080

# Setup an app user so the container doesn't run as the root user
RUN useradd app
USER app

CMD ["uvicorn", "app.main:app", "--host", "0.0.0.0", "--port", "8080"]

Building docker

docker build -t <tag>

Docker processes

docker ps

Exercises

gRPC

gRPC reference: https://grpc.io/docs/ gRPC Java basics: https://grpc.io/docs/languages/java/basics/

Protobuf files

Defining classes:

Important tips:

  • Array in protobuf means repeated field
message Date {
  int32 day = 1; // Number specifies order
  int32 month = 2;
  int32 year = 3;
}

message Location {
  string city = 1;
  string country = 2;
}

message LocationDate {
  Location location = 1;
  Date date = 2;
}

Defining services:

service WeatherReporter {

  //Returning one object
  rpc GetCityWeatherSingleDay(LocationDate) returns (CityWeatherData) {}

  // Returning a stream of objects
  rpc GetCityWeatherMultipleDays(LocationDatePeriod) returns (stream CityWeatherData) {}
}

Example of services and objects with repeated fields

This will be utilized by some of the client side examples underneath

service MetadataService {
  rpc getTrackMetadata(EntitiesRequest) returns (Tracks) {}

  rpc getAlbumMetadata(EntitiesRequest) returns (Albums) {}
}

message EntitiesRequest {
  repeated uint32 id = 1;
}

message Track {
  uint64 id = 1;
  string name = 2;
  string album = 3;
  string artist = 4;
  uint32 duration = 5;
}

message Tracks {
  repeated Track track = 1;
}

message Album {
  uint64 id = 1;
  string name = 2;
  string artist = 3;
  repeated uint32 tracks = 4;
}

message Albums {
  repeated Album album = 1;
}

Generating classes from .proto files

  1. Gradle tab in IDE and press "Tasks > other > generateProto")
  2. The generated classes from the proto file should be in build/generated/source/proto/main folder

Server side

In practice can be done with streams or with simple iteration

public void getCityWeatherSingleDay(LocationDate request, StreamObserver<CityWeatherData> responseObserver) {
	var data = allWeatherData.stream().filter(cityWeatherData -> cityWeatherData.getLocationDate().equals(request)).findFirst().orElse(null);
	if(data != null)responseObserver.onNext(data);
	responseObserver.onCompleted();
}

For returning a stream of data just call onNext multiple times

With iteration:

public void getCityWeatherMultipleDays(LocationDatePeriod request, StreamObserver<CityWeatherData> responseObserver) {
	for(CityWeatherData data : allWeatherData) {
		if(data.getLocationDate().getLocation().equals(request.getLocation())) {
			if(compareDate(data.getLocationDate().getDate(), request.getStartDate()) >= 0 && compareDate(data.getLocationDate().getDate(), request.getEndDate()) <= 0)
			{
				responseObserver.onNext(data);
			}
		}
	}
	responseObserver.onCompleted();
}

With streams:

public void getCityWeatherMultipleDays(LocationDatePeriod request, StreamObserver<CityWeatherData> responseObserver) {
	var startDate = request.getStartDate();
	var endDate = request.getEndDate();
	allWeatherData.stream()
			.filter(cityWeatherData -> cityWeatherData.getLocationDate().getLocation().equals(request.getLocation()))
			.filter(cityWeatherData -> compareDate(cityWeatherData.getLocationDate().getDate(),startDate) >= 0)
			.filter(cityWeatherData -> compareDate(cityWeatherData.getLocationDate().getDate(),endDate) <= 0)
			.forEach(responseObserver::onNext);
	responseObserver.onCompleted();
}

For returning an object which contains array of other objects (stupid???)

public void getAlbumMetadata(EntitiesRequest request, StreamObserver<Albums> responseObserver) {
	Albums.Builder albumsBuilder = Albums.newBuilder();

	for(int i = 0; i < request.getIdCount();i++) {
		// Find the album by its id
		Album album = database.findAlbumById(request.getId(i));

		if(album != null) {
			albumsBuilder.addAlbum(album);
		}
	}

	// In case that an album isn't found builder builds empty list
	Albums albums = albumsBuilder.build();
	responseObserver.onNext(albums);
	responseObserver.onCompleted();
}

If you want to return an error

public void getTrafficData(RouteRequest request, StreamObserver<TrafficResponse> responseObserver) {
	var trafficModel = db.getTrafficModel(request);
	var response = trafficModel.query(request);
	if(response.isPresent()) {
		responseObserver.onNext(response.get());
		responseObserver.onCompleted();
	} else {
		// Just pass an exception with the onError method
		responseObserver.onError(new Exception("No data available."));
	}
}

Client Side

Setup

The blocking stub is a placeholder on which functions are called. It needs to be received from the gRPC object in some way.

public WeatherClient(Channel channel) {
	// Get blocking stub from the gRPC object
	blockingStub = WeatherReporterGrpc.newBlockingStub(channel);
}

or

public SpotifyClient(Channel channel) {
	// spotifyConnection is a wrapper defined in the excercise
	// this is just an example that there can be other ways to get the stub
	this.spotifyConnection = new SpotifyConnection(channel);
	this.blockingStub = spotifyConnection.getStub();
}

Calling method with single object return value

public void getCityWeatherSingleDay(int day, int month, int year, String city, String country) {
	// Need to use builders to create the objects for the request
	Date date = Date.newBuilder().setDay(day).setMonth(month).setYear(year).build();
	Location location = Location.newBuilder().setCity(city).setCountry(country).build();

	// Building the locationDate which will be passed as a parameter
	LocationDate locationDate = LocationDate.newBuilder().setDate(date).setLocation(location).build();

	// Getting the returned object from calling the method on the stub
	CityWeatherData cityWeatherData = blockingStub.getCityWeatherSingleDay(locationDate);

	System.out.println(cityWeatherData.toString());
}

Calling method which returns stream

public void getCityWeatherMultipleDays(int startDay, int startMonth, int startYear, int endDay, int endMonth, int endYear, String city, String country) {
	// Building objects for the request
	Date startDate = Date.newBuilder()
			.setDay(startDay)
			.setMonth(startMonth)
			.setYear(startYear)
			.build();
	Date endDate = Date.newBuilder()
			.setDay(endDay)
			.setMonth(endMonth)
			.setYear(endYear)
			.build();
	Location location = Location.newBuilder().setCity(city).setCountry(country).build();

	// Building LocationDatePeriod object to be passed as parameter
	LocationDatePeriod locationDatePeriod = LocationDatePeriod.newBuilder()
			.setStartDate(startDate)
			.setEndDate(endDate)
			.setLocation(location)
			.build();

	// Method call returns Iterator<CityWeatherData> for the stream of CityWeatherData
	Iterator<CityWeatherData> iterator = blockingStub.getCityWeatherMultipleDays(locationDatePeriod);
	
	// Iterating over the objects
	while (iterator.hasNext()) {
		CityWeatherData cityWeatherData = iterator.next();
		System.out.println(cityWeatherData.toString());
	}
}

Calling method which has parameter with repeated field

public String displayPlaylist(int[] playlist) throws SpotifyClientException {
	StringBuilder stringBuilder = new StringBuilder();

	EntitiesRequest.Builder builder = EntitiesRequest.newBuilder();

	// IMPORTANT for REPEATED fields
	// Add all id's to request
	for(int id : playlist) {
		builder.addId(id);
	}

	EntitiesRequest request = builder.build();

	// Unlike in earlier examplese returns OBJECT which contains multiple Tracks
	Tracks tracks;

	tracks = blockingStub.getTrackMetadata(request);
	if(tracks.getTrackCount() != playlist.length) throw new SpotifyClientException("Failed to get track metadata");


	for(int i = 0; i < tracks.getTrackCount();i++) {
		Track track = tracks.getTrack(i);

		int durationInSeconds = track.getDuration();
		int durationInMinutes = durationInSeconds / 60;
		durationInSeconds = durationInSeconds % 60;

		stringBuilder.append(String.format("%d. %s - %s (%d:%02d)%n", i+1,track.getName(), track.getArtist(), durationInMinutes, durationInSeconds));
	}

	return stringBuilder.toString();
}

Excersises:

  • L02PB01 Weather Reporter
  • L02P01 Spotify gRPC
  • L03PE03 Gobblemaps

ALL RESOURCE LINKS:

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