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rest template exchange method null pointer exception

I am trying the hit the url with rest template exchange but getting null pointer exception at point of executing resttemplate.exchange method.Can you please let me know why i am getting the below null pointer exception

I am trying the hit the url with rest template exchange but getting null pointer exception at point of executing resttemplate.exchange method.Can you please let me know why i am getting the below null pointer exception

I am trying the hit the url with rest template exchange but getting null pointer exception at point of executing resttemplate.exchange method.Can you please let me know why i am getting the below null pointer exception

I am trying the hit the url with rest template exchange but getting null pointer exception at point of executing resttemplate.exchange method.Can you please let me know why i am getting the below null pointer exception

I am trying the hit the url with rest template exchange but getting null pointer exception at point of executing resttemplate.exchange method.Can you please let me know why i am getting the below null pointer exception
I am trying the hit the url with rest template exchange but getting null pointer exception at point of executing resttemplate.exchange method.Can you please let me know why i am getting the below null pointer exception
I am trying the hit the url with rest template exchange but getting null pointer exception at point of executing resttemplate.exchange method.Can you please let me know why i am getting the below null pointer exception

Exception details :

Reached inside ===
Reached === 2
Reached === 3
java.lang.NullPointerException
at com.test.resttemplate.RestTempaltetestApplication.callRestTemplateExchange(RestTempaltetestApplication.java:54)
at com.test.resttemplate.RestTempaltetestApplication.main(RestTempaltetestApplication.java:29)


Here is my code :

package com.test.resttemplate;

import java.io.IOException;
import java.util.Map;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.http.HttpEntity;
import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpMethod;
import org.springframework.http.ResponseEntity;
import org.springframework.web.client.HttpClientErrorException;
import org.springframework.web.client.RestTemplate;

import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;

@SpringBootApplication
public class RestTempaltetestApplication {
private static RestTemplate restTemplate;
@SuppressWarnings("unchecked")
public static void main(String args) {
SpringApplication.run(RestTempaltetestApplication.class, args);

final HttpHeaders headers = new HttpHeaders();
headers.add("materialId", "122344");
Map<String, Object> map;
try {
map = (Map<String, Object>) callRestTemplateExchange("https://alloyui.com/io/data/states.json", headers, HttpMethod.GET, null, Map.class);
System.out.println("Keyssss :"+map.keySet()+"values"+map.values());

} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}

}

@SuppressWarnings("unchecked")
public static Object callRestTemplateExchange(String url, HttpHeaders headers, HttpMethod method, Object body,
Class<?> claszz) throws Exception {
try {
System.out.println("Reached inside === ");
ResponseEntity<Object> response = null;
HttpEntity<?> requestEntity = new HttpEntity<Object>(headers);
System.out.println("Reached === 2");
if (null != body) {
System.out.println("Request === " + convertObjectToString(body));
requestEntity = new HttpEntity<Object>(body, headers);
} else {
requestEntity = new HttpEntity<Object>(headers);
}
System.out.println("Reached === 3");
response = (ResponseEntity<Object>) restTemplate.exchange(url, method, requestEntity, claszz);
if(null!=response.getBody()){
System.out.println("response === " + response.getBody());
}else
System.out.println("response is null");
System.out.println("Reached === 4");
return response.getBody();
} catch (HttpClientErrorException e) {

throw new Exception();
}
}


public final static String convertObjectToString(Object object) {
if (null != object) {
ObjectMapper objectMapper = new ObjectMapper();
try {
Object json = objectMapper.readValue(objectMapper.writeValueAsString(object), Object.class);
return objectMapper.writerWithDefaultPrettyPrinter().writeValueAsString(json);
} catch (JsonMappingException e) {

} catch (IOException e) {

}
}
return null;
}
}


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