Saturday, May 26, 2018

has been blocked by CORS policy: No 'Access-Control-Allow-Origin'

Hi Guys,

This blog is about issues I have faced while fetching data from a REST Web Service.

When I try to get the data from the service I faced an error like ,

Failed to load http://localhost:8090/org.myProject/question: Redirect from 'http://localhost:8090/org.myProject/question' to 'http://localhost:8090/org.myProject/question/' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://localhost:4200' is therefore not allowed access.
This is because the rest service does not provide the response for Http requests from a different domain . The solution to this is add some extra the configuration in the Service to accept requests from a different domains. Lets have a look at the code.
import { EventEmitter, Injectable } from '@angular/core';
import { Headers, Http ,Response} from '@angular/http';
import {  HttpClientModule } from '@angular/common/http';
import {  HttpModule } from '@angular/http';


import 'rxjs/Rx';
import { Observable } from 'rxjs/Observable';

@Injectable()
export class QuestionService{
constructor(private http:Http) {}
loadQuestions(){


return this.http.get('http://localhost:8090/org.myProject/question')
.map(
        (response: Response) => {
          const data = response.json();
       
          return data;
        }
      )
      .catch(
        (error: Response) => {
          return Observable.throw('Something went wrong');
        }
      );

}
}
That's the service,check out the  controller .
import { Component, OnInit } from '@angular/core';
import { QuestionService } from './question.service';


@Component({
  selector: 'app-question',
  templateUrl: './question.component.html',
  styleUrls: ['./question.component.css'],
  providers:[QuestionService]
})
export class QuestionComponent  {

  constructor(private questionService:QuestionService) { }




onGet() {

  this.questionService.loadQuestions().subscribe(
        (questions: any[]) => {this.questions = questions;console.log(questions);},
        (error) => console.log(error)
      );

  }

  var questions;
}

The component file is as below

<div class="container">
<div class="row">
<div>
Question:
<select id="question"  >
<option>Select</option>
<option *ngFor="let question of questions" ngValue="question">{{question.subjectDesc}}</option>
</select>
</div>
</div>
<div class="row">
<div>
 <button class="btn btn-primary" (click)="onGet()">Get Server Response </button>
</div>
</div>

</div>

The change actually has to be done on the server side code . I am using a Spring Web application at the back end . By default it does not respond other hosts. So , Lets add the following entries to web.xml .
<filter>
<filter-name>CORS</filter-name>
<filter-class>com.thetransactioncompany.cors.CORSFilter</filter-class>
</filter>
<filter-mapping>
        <filter-name>CORS</filter-name>
        <url-pattern>/*</url-pattern>
</filter-mapping>

Test once the service is deployed.

Friday, April 13, 2018

SyntaxError: Missing parentheses in call to 'print'

Hi Guys,

You might face an error like "SyntaxError: Missing parentheses in call to 'print'". This usually comes if you have print in your python script or statement . The solution is to replace the print with print() since the syntax is changed from python 3 onwards. 

Saturday, April 7, 2018

unable to marshal type as an element because it is missing an @XmlRootElement annotation


Hi Guys,

This blog is about the error while serializing an xml.

javax.xml.bind.MarshalException
 - with linked exception:
[com.sun.istack.internal.SAXException2: unable to marshal type "test.serializeXML.Request" as an element because it is missing an @XmlRootElement annotation]
at com.sun.xml.internal.bind.v2.runtime.MarshallerImpl.write(MarshallerImpl.java:311)
at com.sun.xml.internal.bind.v2.runtime.MarshallerImpl.marshal(MarshallerImpl.java:236)
at javax.xml.bind.helpers.AbstractMarshallerImpl.marshal(AbstractMarshallerImpl.java:103)
at test.serializeXML.SerializeXML.serialize(SerializeXML.java:16)
at test.Test1.test(Test1.java:16)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.junit.internal.runners.TestMethod.invoke(TestMethod.java:59)
at org.junit.internal.runners.MethodRoadie.runTestMethod(MethodRoadie.java:98)
at org.junit.internal.runners.MethodRoadie$2.run(MethodRoadie.java:79)
at org.junit.internal.runners.MethodRoadie.runBeforesThenTestThenAfters(MethodRoadie.java:87)
at org.junit.internal.runners.MethodRoadie.runTest(MethodRoadie.java:77)
at org.junit.internal.runners.MethodRoadie.run(MethodRoadie.java:42)
at org.junit.internal.runners.JUnit4ClassRunner.invokeTestMethod(JUnit4ClassRunner.java:88)
at org.junit.internal.runners.JUnit4ClassRunner.runMethods(JUnit4ClassRunner.java:51)
at org.junit.internal.runners.JUnit4ClassRunner$1.run(JUnit4ClassRunner.java:44)
at org.junit.internal.runners.ClassRoadie.runUnprotected(ClassRoadie.java:27)
at org.junit.internal.runners.ClassRoadie.runProtected(ClassRoadie.java:37)
at org.junit.internal.runners.JUnit4ClassRunner.run(JUnit4ClassRunner.java:42)
at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:86)
at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:538)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:760)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:460)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:206)
Caused by: com.sun.istack.internal.SAXException2: unable to marshal type "test.serializeXML.Request" as an element because it is missing an @XmlRootElement annotation
at com.sun.xml.internal.bind.v2.runtime.XMLSerializer.reportError(XMLSerializer.java:234)
at com.sun.xml.internal.bind.v2.runtime.ClassBeanInfoImpl.serializeRoot(ClassBeanInfoImpl.java:323)
at com.sun.xml.internal.bind.v2.runtime.XMLSerializer.childAsRoot(XMLSerializer.java:479)
at com.sun.xml.internal.bind.v2.runtime.MarshallerImpl.write(MarshallerImpl.java:308)
... 26 more

Saturday, January 20, 2018

Invalid '@FunctionalInterface' annotation; Greeting is not a functional interface


Lambda expressions are allowed only at source level 1.8 or above https://stackoverflow.com/questions/22544064/java-8-lambdas-dont-work-everything-else-from-java-8-works-though

Sunday, January 14, 2018

StaticInjectorError NullInjectorError: No provider for MyService


Hi Guys,

You might have faced an error like "StaticInjectorError NullInjectorError: No provider for MyService".

This error comes when you try to create a service and something goes wrong.

Let's see the full stack trace.

ERROR Error: StaticInjectorError[MyService]: 
  StaticInjectorError[MyService]: 
    NullInjectorError: No provider for MyService!
    at _NullInjector.get (webpack-internal:///../../../core/esm5/core.js:1189)
    at resolveToken (webpack-internal:///../../../core/esm5/core.js:1477)
    at tryResolveToken (webpack-internal:///../../../core/esm5/core.js:1419)
    at StaticInjector.get (webpack-internal:///../../../core/esm5/core.js:1290)
    at resolveToken (webpack-internal:///../../../core/esm5/core.js:1477)
    at tryResolveToken (webpack-internal:///../../../core/esm5/core.js:1419)
    at StaticInjector.get (webpack-internal:///../../../core/esm5/core.js:1290)
    at resolveNgModuleDep (webpack-internal:///../../../core/esm5/core.js:11074)
    at NgModuleRef_.get (webpack-internal:///../../../core/esm5/core.js:12306)
    at resolveDep (webpack-internal:///../../../core/esm5/core.js:12804)


I have few tips which will help you Debug this.


Let's see the working code
import { Component, OnInit } from '@angular/core';
import { MyService } from './myapp.service';


@Component({
  selector: 'app-question',
  templateUrl: './myapp.component.html',
  styleUrls: ['./myapp.component.css'],
  providers:[MyService ]
})
export class MyComponent implements OnInit {

  constructor(private myService:MyService ) { }
  //constructor() { }
  ngOnInit() {

this.data=this.myService.loadData();
console.log(data);
  }
var data={};

}
In the above code I have successfully created a service .You need to check if you have specified the service in providers.If you have not added ,add it in the provider attribute of @Component decorator .

Apart from this you need to add the service to app.module.ts


import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';
import { FormsModule } from '@angular/forms';
import { HttpModule } from '@angular/http';

import { AppComponent } from './app.component';
import { MyService } from './myapp.service';

@NgModule({
  declarations: [
    AppComponent
  ],
  imports: [
    BrowserModule,
    FormsModule,
    HttpModule
  ],
  providers: [MyService],
  bootstrap: [AppComponent]
})
export class AppModule { }

Friday, December 29, 2017

Uncaught Error: Encountered undefined provider

Hi Guys,

Here is how you can fix the issue "Uncaught Error: Encountered undefined provider" . Have a look at the stack trace below.


compiler.js:485 

Uncaught Error: Encountered undefined provider! Usually this means you have a circular dependencies (might be caused by using 'barrel' index.ts files.
    at syntaxError (compiler.js:485)
    at eval (compiler.js:15725)
    at Array.forEach (<anonymous>)
    at CompileMetadataResolver._getProvidersMetadata (compiler.js:15710)
    at CompileMetadataResolver.getNonNormalizedDirectiveMetadata (compiler.js:14994)
    at CompileMetadataResolver._getEntryComponentMetadata (compiler.js:15812)
    at eval (compiler.js:15293)
    at Array.map (<anonymous>)
    at CompileMetadataResolver.getNgModuleMetadata (compiler.js:15293)
    at JitCompiler._loadModules (compiler.js:34226)


To find out which part of the code is throwing  this error , first have a check in the component.ts file.
Check the value of provider attribute in the @Component decorator .



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