import { Injectable } from '@angular/core';
import { Headers, RequestOptions, Http, Response } from '@angular/http';
import { Observable } from 'rxjs/Observable';
import { Emotion } from './emotion';

import 'rxjs/Rx'; //for operators

@Injectable()
export class ErService {
  private erServerUrl = 'er';

  constructor(private http: Http) {}

  getSampleEmotion(): Observable<Emotion> {
    return this.http.get(this.erServerUrl + '/emotion')
            .map(response => response.json() as Emotion);
  }

  getEmotion(sentence: string): Observable<Emotion> {
    let headers = new Headers({ 'Content-Type': 'application/json' });
    let options = new RequestOptions({ headers: headers });
    return this.http.post(this.erServerUrl + '/sentence', JSON.stringify({sentence: sentence}), options)
            .map(response => response.json() as Emotion);
  }
}

import { Injectable } from '@angular/core';
import { Headers, Http, Response } from '@angular/http';
import { Observable } from 'rxjs/Observable';
import { Emotion } from './emotion';

import 'rxjs/Rx'; //for operators

@Injectable()
export class ErService {
  private erServerUrl = 'er';

  constructor(private http: Http) {}

  getSampleEmotion(): Observable<Emotion> {
    return this.http.get(this.erServerUrl + '/emotion')
            .map(response => response.json() as Emotion);
  }

  getEmotion(sentence: string): Observable<Emotion> {
    return this.http.post(this.erServerUrl + '/sentence', sentence)
            .map(response => response.json() as Emotion);
  }
}

--- 
+++ 
@@ -1,5 +1,5 @@
 import { Injectable } from '@angular/core';
-import { Headers, Http, Response } from '@angular/http';
+import { Headers, RequestOptions, Http, Response } from '@angular/http';
 import { Observable } from 'rxjs/Observable';
 import { Emotion } from './emotion';
 
@@ -17,7 +17,9 @@
   }
 
   getEmotion(sentence: string): Observable<Emotion> {
-    return this.http.post(this.erServerUrl + '/sentence', sentence)
+    let headers = new Headers({ 'Content-Type': 'application/json' });
+    let options = new RequestOptions({ headers: headers });
+    return this.http.post(this.erServerUrl + '/sentence', JSON.stringify({sentence: sentence}), options)
             .map(response => response.json() as Emotion);
   }
 }
Call sentence POST API with content-type json
