node.js前端运行在localhost:3000,
通过ajax获取运行在8080端口的java服务返回的数据报了这个错误：
（local:8080/wechat/api/alarms/1）

XMLHttpRequest cannot load http://localhost:8080/wechat/api/alarms/1. Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://localhost:3000' is therefore not allowed access.

js---------------------------------------------------------------------
var alarmUrl='http://localhost:8080/wechat/api/alarms';
mui.ajax({

                    url:alarmUrl+'/'+page,
                    type:'GET',
                    dataType:'json',
                    success:function(data){
                        console.log(data);
                    },
                    error:function(xhr,type,errorThrown){
                        //打印报错
                        console.log(xhr+'\n'+type+'\n'+errorThrown);
                    }
                    
                    

java-------------------------------------------------------------------
通过RESTful API接口对外提供数据

接口uri：
/wechat/api/alarms/{page}

node--app.js代码-----------------------------------------------------------
var express=require('express');
var app=express();
var path=require('path');
var logger = require('morgan');//logger（记录器），在控制台中，显示req请求的信息。
var http=require('http')
//bodyParser用于解析客户端请求的body中的内容,内部使用JSON编码处理,url编码处理以及对于文件的上传处理.
var bodyParser=require('body-parser');
var favicon=require('serve-favicon');
var cookieParser=require('cookie-parser');
var session=require('express-session');

var news_main=require('./routes/news_main');
var pullrefresh_sub=require('./routes/pullrefresh_sub');
var boiler_alarm=require('./routes/boiler_alarm')
var login=require('./routes/login');

app.use(session({

secret:'a~Kf?)P{3490*&(',//密码字符串
maxAge:3600000,//定制session的会话时长
resave:true,//是否每次都保存
saveUninitialized:true

}));

//var news_page=require('./routes/news_page');
// app.get('/',function(req,res){
// res.render('news_main');
// });

// 定义模板
app.set('views',path.join(__dirname,'views'));
app.engine('html',require('ejs').renderFile);
app.set('view engine','html');
//静态文件目录，
app.use(express.static(path.join(__dirname,'public')));

app.use(logger('dev'));
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({

extended:false

}));

app.use(cookieParser());

/**
*路由配置
*/
app.use('/',news_main);
app.use('/pull',pullrefresh_sub);
app.use('/alarm',boiler_alarm);
app.use('/',login);

var server=app.listen(3000,function(){

var host=server.address().address;
var port=server.address().port;
console.log("Example boiler listing at http://%s:%s",host,port);

});

node---boiler_alarm.js(路由部分代码) -------------------------------------------------------

var express=require('express');
var router=express.Router();
router.get('/',function(req,res,next){

res.render('boiler_alarm',{
    title:'报警模块'
});

});

这里网上看到加这个，但是没用
//router.use(function (req, res, next) {
//res.header("Access-Control-Allow-Origin", "*");
//res.header("Access-Control-Allow-Headers", "X-Requested-With");
//res.header("Access-Control-Allow-Methods", "PUT,POST,GET,DELETE,OPTIONS");
//next();
//});

module.exports=router;