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Get access token from Oauth2 rest api using java

I need to call Oauth2 ResT API service to fetch the access token and expire_in values from the JSON file by it.
Below is a sample CURL which i need to call using JAVA i am beginner in JAVA so not able to figure out how to do it however i can do it using shell script.
curl -u 'ClientId:Clientaccesskey' https://oauth2.url/oauth/token -X POST -d 'response_type=token&client_id=ClientId&username=user&password=userpassword&scope=process&grant_type=password'
Sample JSON retured by above curl command --
{"access_token":"accessTokentobefetched","token_type":"bearer","refresh_token":"refreshToken","expires_in":7199,"scope":"process","jti":"somehexadecimalvaliu"}
In shell script we can fetch the value of access token and other fields using AWK command and other commands.
So i need to call this CURL command in JAVA and fetch the value of access token and other keys from the JSON file.
Any help which can help me start with this is welcome as i am new to JAVA and learning.

There are quite a few libraries that you can use to help you make a regular HTTP POST request from Java, but since you seem to require to send plain text/plain body content - I suggest that you use okhttp3. This is a fairly lightweight and easy to work with HTTP client.
You will need to add the following dependency to your pom.xml, grabbed from https://mvnrepository.com/artifact/com.squareup.okhttp3/okhttp/4.7.2:
<!-- https://mvnrepository.com/artifact/com.squareup.okhttp3/okhttp -->
<dependency>
<groupId>com.squareup.okhttp3</groupId>
<artifactId>okhttp</artifactId>
<version>4.7.2</version>
</dependency>
If you are using gradle, just visit the before mentioned URL, and get the gradle equivalent dependency declaration.
And here's a complete class that illustrates how the okhttp3 client can be used to perform the POST request, and extract the return value. This example expects that you are using the spring-boot-starter-web dependency (this will include the jackson and tomcat libraries that are used in the example).
package com.example.demo;
import com.fasterxml.jackson.databind.ObjectMapper;
import okhttp3.*;
import org.apache.tomcat.util.codec.binary.Base64;
import org.springframework.stereotype.Component;
import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.util.HashMap;
import java.util.Map;
#Component
public class TokenRequester {
public String getAccessToken() throws IOException {
// Create a new HTTP client
OkHttpClient client = new OkHttpClient().newBuilder().build();
// Create the request body
MediaType mediaType = MediaType.parse("text/plain");
RequestBody body = RequestBody.create(mediaType, "response_type=token&client_id=ClientId&username=user&password=userpassword&scope=process&grant_type=password");
// Build the request object, with method, headers
Request request = new Request.Builder()
.url("https://oauth2.url/oauth/token")
.method("POST", body)
.addHeader("Authorization", createAuthHeaderString("ClientId", "Clientaccesskey"))
.addHeader("Content-Type", "text/plain")
.build();
// Perform the request, this potentially throws an IOException
Response response = client.newCall(request).execute();
// Read the body of the response into a hashmap
Map<String,Object> responseMap = new ObjectMapper().
readValue(response.body().byteStream(), HashMap.class);
// Read the value of the "access_token" key from the hashmap
String accessToken = (String)responseMap.get("access_token");
// Return the access_token value
return accessToken;
}
// Just a helper metod to create the basic auth header
private String createAuthHeaderString(String username, String password) {
String auth = username + ":" + password;
byte[] encodedAuth = Base64.encodeBase64(auth.getBytes(StandardCharsets.US_ASCII));
String authHeader = "Basic " + new String(encodedAuth);
return authHeader;
}
}
You may need to tweak a few things here. I could ask you to supply me the verbose output from the curl command, in order to be sure about the encoding - but give this one a try and see what you get?

Here's a solution that involves only Spring, using a RestTemplate for the POST request.
I found that when you use curl -X POST -d 'key=data', curl will add the header content-type: application/x-www-form-urlencoded, so the solution here will do the same.
This solution sets up the RestTemplate with the headers and body you have specified, and captures the response in an object equivalent to the one you have described.
The following solution consists of two files that you can try to introduce into your solution:
RestTemplateTokenRequester.java
package com.example.demo;
import org.apache.tomcat.util.codec.binary.Base64;
import org.springframework.http.*;
import org.springframework.stereotype.Component;
import org.springframework.util.LinkedMultiValueMap;
import org.springframework.util.MultiValueMap;
import org.springframework.web.client.RestTemplate;
import java.nio.charset.StandardCharsets;
#Component
public class RestTemplateTokenRequester {
public TokenResponse requestAccessToken() {
// Create a RestTemplate to describe the request
RestTemplate restTemplate = new RestTemplate();
// Specify the http headers that we want to attach to the request
HttpHeaders headers = new HttpHeaders();
headers.setContentType(MediaType.APPLICATION_FORM_URLENCODED);
headers.add("Authorization", createAuthHeaderString("ClientId", "Clientaccesskey"));
// Create a map of the key/value pairs that we want to supply in the body of the request
MultiValueMap<String, String> map = new LinkedMultiValueMap<>();
map.add("response_type","token");
map.add("client_id","ClientId");
map.add("username","user");
map.add("password","userpassword");
map.add("scope","process");
map.add("grant_type","password");
// Create an HttpEntity object, wrapping the body and headers of the request
HttpEntity<MultiValueMap<String, String>> entity = new HttpEntity<>(map, headers);
// Execute the request, as a POSt, and expecting a TokenResponse object in return
ResponseEntity<TokenResponse> response =
restTemplate.exchange("https://oauth2.url/oauth/token",
HttpMethod.POST,
entity,
TokenResponse.class);
return response.getBody();
}
// Just a helper metod to create the basic auth header
private String createAuthHeaderString(String username, String password) {
String auth = username + ":" + password;
byte[] encodedAuth = Base64.encodeBase64(auth.getBytes(StandardCharsets.US_ASCII));
String authHeader = "Basic " + new String(encodedAuth);
return authHeader;
}
}
TokenResponse.java
This is simply a POJO that is used by the jackson mapper, to capture the response in an object that you can easily read your result from.
package com.example.demo;
import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
import com.fasterxml.jackson.annotation.JsonProperty;
#JsonIgnoreProperties(ignoreUnknown = true)
public class TokenResponse {
#JsonProperty("access_token")
private String accessToken;
#JsonProperty("token_type")
private String tokenType;
#JsonProperty("refresh_token")
private String refreshToken;
#JsonProperty("expires_in")
private Integer expiresIn;
#JsonProperty("scope")
private String scope;
#JsonProperty("jti")
private String jti;
}
I hope this solution will help you - I would prefer it over the other solution I have suggested with okhttp3.

curl is a HTTP client.
better solution is using HTTP client APIs for java to call endpoints.
RestTemplate is common HTTP client comes with spring and it is your best choice.

Can we call external API without API ID?

I am new to API design, I am working on one project where I need to call currency exchange API from National Bank of Poland http://api.nbp.pl but I do not see any indication where I can find API ID. This development is on Spring Boot if I am trying to run the application without API ID it is throwing 404 error.
Here is the piece of code that I have written.
#RequestMapping(method = RequestMethod.GET, value = "/exchangerates/rates/{table}/{code}")
public #ResponseBody Object getAllCurriencyExchangeRates(#PathVariable String table, #PathVariable String code) {
RestTemplate restTemplate = new RestTemplate();
HttpHeaders headers = new HttpHeaders();
ResponseEntity<Object> response =
restTemplate.getForEntity("http://api.nbp.pl/api/" +table+ "," +code+ Object.class, null, headers);
return response;
}
Actual query http://api.nbp.pl/api/exchangerates/rates/a/chf/
So, my question is can we call an external API without API ID?

First things first, you are trying to reach wrong API. That is why you are getting 404 not found. 404 means there is no url like you are calling.
Check your restTemplate carefully,
restTemplate.getForEntity("http://api.nbp.pl/api/" + table+ "," +code+ Object.class, null, headers);
You are doing wrong when concatenate strings.
It should look something like this;
restTemplate.getForEntity("http://api.nbp.pl/api/exchangerates/rates/"+table+"/"+code, Object.class, null, headers);
And a hint for API developers, firstly you should play with api using Postman and then write code with api.

Try this - I have tested it - it works. Please keep in mind this is just a test implementation. Things inside main method have to be copied into your getAllCurriencyExchangeRates method.
And for sure replace "a" and "chf" through variables. I assume table and code are the variables you want to use. I used String because I don't know which type of object you want to return. You can use your own pojo for sure instead of String.
package scripts;
import java.net.URI;
import org.springframework.http.ResponseEntity;
import org.springframework.web.client.RestOperations;
import org.springframework.web.client.RestTemplate;
import org.springframework.web.util.UriComponentsBuilder;
/**
* author: flohall
* date: 08.12.19
*/
public class Test {
public static void main(final String[] args){
final String url = "http://api.nbp.pl/api/exchangerates/rates";
final URI uri = UriComponentsBuilder.fromHttpUrl(url).path("/").path("a").path("/").path("chf").build().toUri();
System.out.println(uri);
final RestOperations restTemplate = new RestTemplate();
final ResponseEntity<String> result = restTemplate.getForEntity(uri, String.class);
System.out.println(result.getBody());
}
}

Try with this
ResponseEntity<Object> response =
restTemplate.getForEntity("http://api.nbp.pl/api/exchangerates/rates/" + table + "/" + code, Object.class, headers);

Spring Boot Get Request with JSON [duplicate]

I am trying to access the contents of an API and I need to send a URL using RestTemplate.
String url1 = "http://api.example.com/Search?key=52ddafbe3ee659bad97fcce7c53592916a6bfd73&term=&limit=100&sort={\"price\":\"desc\"}";
OutputPage page = restTemplate.getForObject(url1, OutputPage .class);
But, I am getting the following error.
Exception in thread "main" java.lang.IllegalArgumentException: Not enough variable values available to expand '"price"'
at org.springframework.web.util.UriComponents$VarArgsTemplateVariables.getValue(UriComponents.java:284)
at org.springframework.web.util.UriComponents.expandUriComponent(UriComponents.java:220)
at org.springframework.web.util.HierarchicalUriComponents.expandInternal(HierarchicalUriComponents.java:317)
at org.springframework.web.util.HierarchicalUriComponents.expandInternal(HierarchicalUriComponents.java:46)
at org.springframework.web.util.UriComponents.expand(UriComponents.java:162)
at org.springframework.web.util.UriTemplate.expand(UriTemplate.java:119)
at org.springframework.web.client.RestTemplate.execute(RestTemplate.java:501)
at org.springframework.web.client.RestTemplate.getForObject(RestTemplate.java:239)
at hello.Application.main(Application.java:26)
If I remove the sort criteria, it is working properly.
I need to parse the JSON using sort criteria.
Any help will be much appreciated.
Thanks

The root cause is that RestTemplate considers curly braces {...} in the given URL as a placeholder for URI variables and tries to replace them based on their name. For example
{pageSize}
would try to get a URI variable called pageSize. These URI variables are specified with some of the other overloaded getForObject methods. You haven't provided any, but your URL expects one, so the method throws an exception.
One solution is to make a String object containing the value
String sort = "{\"price\":\"desc\"}";
and provide a real URI variable in your URL
String url1 = "http://api.example.com/Search?key=52ddafbe3ee659bad97fcce7c53592916a6bfd73&term=&limit=100&sort={sort}";
You would call your getForObject() like so
OutputPage page = restTemplate.getForObject(url1, OutputPage.class, sort);
I strongly suggest you do not send any JSON in a request parameter of a GET request but rather send it in the body of a POST request.

If the solution suggested by sotirios-delimanolis is a little difficult to implement in a scenario, and if the URI string containing curly braces and other characters is guaranteed to be correct, it might be simpler to pass the encoded URI string to a method of RestTemplate that hits the ReST server.
The URI string can be built using UriComponentsBuilder.build(), encoded using UriComponents.encode(), and sent using RestTemplate.exchange() like this:
public ResponseEntity<Object> requestRestServer()
{
HttpEntity<?> entity = new HttpEntity<>(requestHeaders);
UriComponentsBuilder builder = UriComponentsBuilder.fromUriString(rawValidUrl)
.queryParams(
(LinkedMultiValueMap<String, String>) allRequestParams);
UriComponents uriComponents = builder.build().encode();
ResponseEntity<Object> responseEntity = restTemplate.exchange(uriComponents.toUri(), HttpMethod.GET,
entity, String.class);
return responseEntity;
}
Building, encoding, and extracting URI have been seperated out for clarity in the above code snippet.

You can URL encode the parameter values:
String url1 = "http://api.example.com/Search?key=52ddafbe3ee659bad97fcce7c53592916a6bfd73&term=&limit=100&sort=";
org.apache.commons.codec.net.URLCodec codec = new org.apache.commons.codec.net.URLCodec();
url1 = url1 + codec.encode("{\"price\":\"desc\"}");
OutputPage page = restTemplate.getForObject(url1, OutputPage.class);

You can set a specific UriTemplateHandler in your restTemplate. This handler would just ignore uriVariables :
UriTemplateHandler skipVariablePlaceHolderUriTemplateHandler = new UriTemplateHandler() {
#Override
public URI expand(String uriTemplate, Object... uriVariables) {
return retrieveURI(uriTemplate);
}
#Override
public URI expand(String uriTemplate, Map<String, ?> uriVariables) {
return retrieveURI(uriTemplate);
}
private URI retrieveURI(String uriTemplate) {
return UriComponentsBuilder.fromUriString(uriTemplate).build().toUri();
}
};
restTemplate.setUriTemplateHandler(skipVariablePlaceHolderUriTemplateHandler);

You can encode url before using RestTemplate
URLEncoder.encode(data, StandardCharsets.UTF_8.toString());

You can simply append a variable key to the URL and give the value using the restTemplate.getForObject() method.
Example:
String url = "http://example.com/api?key=12345&sort={data}";
String data="{\"price\":\"desc\"}";
OutputPage page = restTemplate.getForObject(url, OutputPage.class, data);

How to consume a HTTPS GET service with Spring Boot

I am trying to consume the following HTTPS endpoints from Yahoo Weather Service:
Yahoo Weather Service API
I am doing some special query according to the API to get the current weather at some parametrized location.
#Service("weatherConditionService")
public class WeatherConditionServiceImpl implements WeatherConditionService {
private static final String URL = "http://query.yahooapis.com/v1/public/yql";
public WeatherCondition getCurrentWeatherConditionsFor(Location location) {
RestTemplate restTemplate = new RestTemplate();
StringBuilder stringBuilder = new StringBuilder();
stringBuilder.append(URL);
stringBuilder.append("?q=select%20item.condition%20from%20weather.forecast%20where%20woeid%20in%20(select%20woeid%20from%20geo.places(1)%20where%20text%3D%22");
// TODO: Validate YQL query injection
stringBuilder.append(location.getName());
stringBuilder.append("%22)&format=json&env=store%3A%2F%2Fdatatables.org%2Falltableswithkeys");
WeatherQuery weatherQuery = restTemplate.getForObject(stringBuilder.toString(), WeatherQuery.class);
// TODO: Test Json mapping response
Condition condition = weatherQuery.getQuery().getResults().getChannel().getItem().getCondition();
return new WeatherCondition(condition.getDate(), Integer.parseInt(condition.getTemp()), condition.getText());
}
Location is a class that provides the attribute "name" that is a String description of the location, such as "New York" or "Manila".
Condition an other classes just map the returning object.
When executing I get the following HTTP response:
org.springframework.web.client.HttpClientErrorException: 403 Forbidden
So this means I am not authorized to access the resource from what I understand.
The URL works great if I just copy & paste it in a web browser:
Yahoo Weather Query
I think that mapping is not a problem since I am not getting "400" (Bad Request) but "403" (Forbidden)
There must be some error on the way I use the RestTemplate object. I am researching but I can't find an answer.

The docs say you need an api key. But when I make a call like this:
fetch('https://query.yahooapis.com/v1/public/yql?q=select%20*%20from%20weather.forecast%20where%20woeid%20in%20(select%20woeid%20from%20geo.places(1)%20where%20text%3D%22nome%2C%20ak%22)&format=json&env=store%3A%2F%2Fdatatables.org%2Falltableswithkeys')
.then(resp=> resp.json())
.then((res)=>console.log(res.query.results))
https://repl.it/NeoM
It works fine without one. Perhaps you've been blackisted for hitting the api too often.
Your code seems fine.

I finally found the answer. It finally WAS a Bad Request because I needed to pass the parameters differently (not as part of the URL).
I found the answer here. Here goes the code for my particular Yahoo Weather API call return a String (I still will have to do some work to use the mapping).
private static final String URL = "http://query.yahooapis.com/v1/public/yql";
public String callYahooWeatherApi() {
RestTemplate restTemplate = new RestTemplate();
HttpHeaders headers = new HttpHeaders();
headers.set("Accept", MediaType.APPLICATION_JSON_VALUE);
UriComponentsBuilder builder = UriComponentsBuilder.fromHttpUrl(URL)
.queryParam("q", "select wind from weather.forecast where woeid=2460286")
.queryParam("format", "json");
HttpEntity<?> entity = new HttpEntity<>(headers);
HttpEntity<String> response = restTemplate.exchange(
builder.build().encode().toUri(),
HttpMethod.GET,
entity,
String.class);
return response.getBody();
}

spring android resttemplate encoding url

I use Spring android RestTemplate to execute GET request to Youtube API like this:
// build rest template
RestTemplate restTemplate = new RestTemplate();
GsonHttpMessageConverter jsonConverter = new GsonHttpMessageConverter();
FormHttpMessageConverter formHttpMessageConverter = new FormHttpMessageConverter();
StringHttpMessageConverter stringHttpMessageConverter = new StringHttpMessageConverter();
final List<HttpMessageConverter<?>> listHttpMessageConverters = restTemplate.getMessageConverters();
listHttpMessageConverters.add(jsonConverter);
listHttpMessageConverters.add(formHttpMessageConverter);
listHttpMessageConverters.add(stringHttpMessageConverter);
restTemplate.setMessageConverters(listHttpMessageConverters);
Uri.Builder uriBuilder = Uri.parse(https://www.googleapis.com/youtube/v3/channels).buildUpon();
uriBuilder.appendQueryParameter("key", API_KEY);
uriBuilder.appendQueryParameter("part", "id,snippet");
uriBuilder.appendQueryParameter("forUsername", channelName);
String url = uriBuilder.build().toString(); // this is right url
// like this: https://www.googleapis.com/youtube/v3/channels?key=MY_KEY&part=id%2Csnippet&forUsername=cnn
MyEntity result = restTemplate.getForObject(url, MyEntity.class);
From debug, I can see RestTemplate execute wrong url and I got 400 bad request error:
03-16 12:06:47.651: W/RestTemplate(24970): GET request for
"https://www.googleapis.com/youtube/v3/channels?key=MY_KEY&part=id%252Csnippet&forUsername=cnn"
resulted in 400 (Bad Request); invoking error handler
I have no idea why RestTemplate try to encode parameter url again, from id%2Csnippet to id%252Csnippet
Is there any way to correct it?

It just so happens that the RestTemplate#getForObject(..) method that expects a String builds a URI from the given String and encodes it before using it. It uses custom Spring classes to do this. (See the source code.)
You can fix this issue by creating a URI object from your String and pass that to the method.
String url = uriBuilder.build().toString(); // this is right url
URI uri = new URI(url);
MyEntity result = restTemplate.getForObject(uri, MyEntity.class);