Context initialization failed

Context initialization failed
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'userController': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: private edu.scramjet.service.AppUserService edu.scramjet.controller.UserController.appUserService; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type [edu.scramjet.service.AppUserService] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}

Solution :
If you look at stack. Spring container is unable to create bean. for userController. unable to autowire the appUserService.

ex :  public class void UserController {
 
       @Autowired
private AppUserService appUserService;     ///  interface object

      @RequestMapping(value="/create",method=RequestMethod.POST,
produces=MediaType.APPLICATION_JSON_VALUE,
consumes=MediaType.APPLICATION_JSON_VALUE)
public User createAppUser(@RequestBody User user ){
System.out.println(user);

appUserService.createUser();



return user;
}

   
     }

If AppUserService  is object  interface and its autowired. We need to provide Implementation class for bean creation.


public interface AppUserService {

public void createUser();
}

@Service
public interface AppUserService implements  AppUserServiceImpl {

public void createUser() {

}

}

Java 8 JDBC

Java 8 : The JDBC-ODBC Bridge has been removed.

There is plenty of option to try. refer the Stackoverflow for futher references. 

Java 1.8 Concurrency feature "ConcurrentHashMap as a Set"

Java 1.8 Concurrency feature "ConcurrentHashMap as a Set"

The feature will return set of key in the map as Set.

public class VoiceConcurrentHashMap {

public static void main(String[] args) {

ConcurrentHashMap<String,String> map = new ConcurrentHashMap<String, String>();
System.out.println(map);
map.put("Lnkedin", "Networking");
map.put("Microsoft", "Windows10");
map.put("facebook", "Social");
map.put("Google", "SearchEngine");

KeySetView<String,String> set = map.keySet();
System.out.println(set);
}

}

Result : [Google, facebook, Microsoft, Lnkedin] .

Image :

ref :
Java API 

Behaviour of ConcurrentHashMap when it has Duplicate key.

Behaviour of ConcurrentHashMap when it has Duplicate key.

ConcurrentHashMap will overwrite previous value for a given key in Map. The object whos reference is lost are eligible for garage collection.

public class VoiceConcurrentHashMap {

public static void main(String[] args) {

ConcurrentHashMap<String,String> map = new ConcurrentHashMap<String, String>();
System.out.println(map);
map.put("Lnkedin", "profile");
map.put("Lnkedin", "profile");
map.put("Lnkedin", "jagdeesh");

}
}

ref :
1. Java API
2. Stackoverflow

Can not deserialize instance of java.util.ArrayList out of START_OBJECT token

com.fasterxml.jackson.databind.JsonMappingException: Can not deserialize instance of java.util.ArrayList out of START_OBJECT token

When supplying json object from postman. if Class contain a list object. Provide it as a array [].
ex :
{
    "name" : "raman",
    "employeeId" : 12345,
"orderList" : {"orderId" : 1,"orderName" : "rest json book"}
}
solution :
{
"name" : "raman",
"employeeId" : 12345,
"orderList" : [{"orderId" : 1,"orderName" : "rest json book"}]
}

@JsonIgnore

@JsonIgnore

If we want to serialize object to json, during this process some of the property can be null/empty can be ignored.
this can be achived using @jsonIgnore.

ex :
1. @JsonIgnore(Include.NON_NULL)
2. @JsonIgnore(Include.NON_EMPTY)
3. @JsonIgnore(Include.NON_DEFAULT)

Ref : wilddiary

use of @JsonSerialize

use of @JsonSerialize

A pojo class which is participating is serialisationtion should be annoted with @JsonSerialize