java.lang.AbstractMethodError

Lets understand what it is:

AbstractMethodError Thrown when an application tries to call an abstract method. Normally, this error is caught by the compiler; this error can only occur at run time if the definition of some class has incompatibly changed since the currently executing method was last compiled.

How did I encounter java.lang.AbstractMethodError

Well I was having two spring project

• UserLib : Lib which having core classes
• MasterLib : Lib which is having dependency of UserLib

UserLib  had class

RegisterUser.java

public class RegisterUser{
public void register() {
// stuff to register
}
}

MasterLib was using RegisterUser class

public class UserService extends RegisterUser{ public  void doRegister() { UserService  user = new UserService (); user .register();

}
}

I had made build of UserLib  and run Master lib it worked; but for some reason I had make RegisterUser class as abstract class so I made it but, I forgot make build of UserLib and I simple run my masterLib, that is where I encountered this issue.

How to solve java.lang.AbstractMethodError : Either don't go for abstract method approach; or you just have implementation of the abstract class and don't forget to make build :) if you are have project structure like me.

Caused by: java.net.ProtocolException: cannot write to a URLConnection if doOutput=false - call setDoOutput(true)

Caused by: java.net.ProtocolException: cannot write to a URLConnection if doOutput=false - call setDoOutput(true)

It was happened to be issue while I was using HttpEntity and pass header in resttemplates exchange method
I was adding parameters in entity when I removed it, it worked.

What I was doing

            RestTemplate _restTemplate =new RestTemplate();
MediaType mediaType = new MediaType("application", "json", Charset.forName("UTF-8"));
HttpHeaders headers = new HttpHeaders();
headers.setContentType(mediaType);
headers.add("x-request-id",requestId);
HttpEntity<String> entity = new HttpEntity("parameters", headers); //Issue was here
long startTime = System.currentTimeMillis();
ResponseEntity<Map> result = _restTemplate.exchange("myURL?paramKey={para1}", HttpMethod.GET, entity, Map.class, "paramValue");
  
How did I fix it:

RestTemplate _restTemplate =new RestTemplate();
MediaType mediaType = new MediaType("application", "json", Charset.forName("UTF-8"));
HttpHeaders headers = new HttpHeaders();
headers.setContentType(mediaType);
headers.add("x-request-id",requestId);
HttpEntity<String> entity = new HttpEntity(headers); //Fixed issue
long startTime = System.currentTimeMillis();
ResponseEntity<Map> result = _restTemplate.exchange("myURL?paramKey={para1}", HttpMethod.GET, entity, Map.class, "paramValue");

What was happening:

HttpEntity<String> entity = new HttpEntity("parameters", headers);here parameters were treated as body.

Caused by: java.lang.IllegalArgumentException: Conflicting setter definitions for property "AttributeStatus": com.pkj.Clazz#setAttributeSource(1 params) vs com.pkj.Clazz#setAttributeStatus(1 params)

Symptoms :

1. You are using com.fasterxml.jackson.databind ObjectMapper
2. By using object of ObjectMapper you are possibly trying Convert Json to POJO
3. All problem lies in your POJO class

Solution:

1.  Go to your POJO class i.e. Clazz in my case
2. checkout the property or variable named "AttributeStatus"
3. In my case  I had added   @JsonProperty("AttributeSource") on two properties or variables
4. So corrected that and it worked, meaning I had put correct @JsonProperty on respective variables.

i.e. 

 Before

     @JsonProperty("AttributeSource") 

      private String AttributeSource

     @JsonProperty("AttributeSource") 

      private String AttributeDestination

After

     @JsonProperty("AttributeSource") 

      private String AttributeSource

     @JsonProperty("AttributeDestination") 

      private String AttributeDestination

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