使用angular服务传递json数据

我一直试图通过json请求使用angular2服务将数据发布到节点api。但是，当我通过angular2服务传递参数时，我的节点api接收到

未定义的值。
下面是我的角度服务代码

 enrolldegree(name,depart,enrollnumber,cgpa,university,token){
 let peer = '["localhost:10151","localhost:10351"]';
 let fcn = 'initDegree';    
 let argument = '["'+name+'","'+depart+'","'+enrollnumber+'","'+cgpa+'","'+university+']';
 let headers = new Headers({'cache-control':'no-cache', 'Content-Type': 'application/json', 'authorization':'Bearer '+token});
 let options = new RequestOptions({ headers: headers });
 let body1 = new URLSearchParams();
 body1.set('peers','["localhost:10151","localhost:10351"]');
 body1.set('fcn',fcn);
 body1.set('args',argument);
 let body = JSON.stringify(body1);
 console.log('server logs',body);
 return this.http.post('http://localhost:4000/channels/mychannel/chaincodes/mycc', body, options )
.map((res: Response) => res.json())
.catch((error:any) => Observable.throw(error.json().error || 'Server error shit bang in'));
}

这是我的节点api代码

  app.post('/channels/:channelName/chaincodes/:chaincodeName', function(req, res) {
logger.debug('==================== INVOKE ON CHAINCODE ==================');
var peers = req.body.peers;
var chaincodeName = req.params.chaincodeName;
var channelName = req.params.channelName;
var fcn = req.body.fcn;
var args = req.body.args;
logger.debug('channelName  : ' + channelName);
logger.debug('chaincodeName : ' + chaincodeName);
logger.debug('fcn  : ' + fcn);
logger.debug('args  : ' + args);
if (!peers || peers.length == 0) {
    res.json(getErrorMessage('\'peers\''));
    return;
}
if (!chaincodeName) {
    res.json(getErrorMessage('\'chaincodeName\''));
    return;
}
if (!channelName) {
    res.json(getErrorMessage('\'channelName\''));
    return;
}
if (!fcn) {
    res.json(getErrorMessage('\'fcn\''));
    return;
}
if (!args) {
    res.json(getErrorMessage('\'args\''));
    return;
}

invoke.invokeChaincode(peers, channelName, chaincodeName, fcn, args, req.username, req.orgname)
.then(function(message) {
    res.send(message);
});
 });

当我尝试使用curl查询发布数据时，一切都很好。这是我在发出post请求时使用的curl查询

curl -s -X POST \
  http://localhost:4000/channels/mychannel/chaincodes/mycc \
  -H "authorization: Bearer $ORG1_TOKEN" \
  -H "content-type: application/json" \
  -d '{
    "peers": ["localhost:7051", "localhost:8051"],
    "fcn":"initDegree",
    "args":["Khurrum","software","Ned11831314","3.5","Ned"]
}'

我在angular2服务中做错了什么？
在angular2服务代码中，不要将请求主体创建为URLSearchParams实例，请尝试以下操作：

let body1 = {
 peers: ["localhost:10151","localhost:10351"],
 fcn: fcn,
 args: argument
}
let body = JSON.stringify(body1);