03、获取access_token

https://mp.weixin.qq.com/wiki?t=resource/res_main&id=mp1421140183
获取access_token
access_token是公众号的全局唯一接口调用凭据，公众号调用各接口时都需使用access_token。开发者需要进行妥善保存（存储进数据库或者缓存中）。access_token的存储至少要保留512个字符空间。access_token的有效期目前为2个小时，需定时刷新，重复获取将导致上次获取的access_token失效。
公众平台的API调用所需的access_token的使用及生成方式说明：
1、建议公众号开发者使用中控服务器统一获取和刷新Access_token，其他业务逻辑服务器所使用的access_token均来自于该中控服务器，不应该各自去刷新，否则容易造成冲突，导致access_token覆盖而影响业务；
2、目前Access_token的有效期通过返回的expire_in来传达，目前是7200秒之内的值。中控服务器需要根据这个有效时间提前去刷新新access_token。在刷新过程中，中控服务器可对外继续输出的老access_token，此时公众平台后台会保证在5分钟内，新老access_token都可用，这保证了第三方业务的平滑过渡；
3、Access_token的有效时间可能会在未来有调整，所以中控服务器不仅需要内部定时主动刷新，还需要提供被动刷新access_token的接口，这样便于业务服务器在API调用获知access_token已超时的情况下，可以触发access_token的刷新流程。
公众号可以使用AppID和AppSecret调用本接口来获取access_token。AppID和AppSecret可在“微信公众平台-开发-基本配置”页中获得（需要已经成为开发者，且帐号没有异常状态）。
调用接口时，请登录“微信公众平台-开发-基本配置”提前将服务器IP地址添加到IP白名单中，点击查看设置方法，否则将无法调用成功。

 /**
     * 获取accesstoken
     * @return
     */
    @GetMapping("/getAccessToken")
    public String getAccessToken() {
        String url = WechatUrl.GET_ACCESS_TOKEN
                .replaceAll("#APPID#", WechatConf.APPID)
                .replaceAll("#APPSECRET#", WechatConf.APPSECRET);
        return HttpConnectionUtil.get(url);
    }

package com.lm.util;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.Map;

public class HttpConnectionUtil {
    //get请求
    public static String get(String url){
        HttpURLConnection conn = null;
        BufferedReader rd = null ;
        StringBuilder sb = new StringBuilder ();
        String line = null ;
        String response = null;
        try {
            conn = (HttpURLConnection) new URL(url).openConnection();
            conn.setRequestMethod("GET");
            conn.setDoInput(true);
            conn.setReadTimeout(20000);
            conn.setConnectTimeout(20000);
            conn.setUseCaches(false);
            conn.connect();
            rd  = new BufferedReader( new InputStreamReader(conn.getInputStream(), "UTF-8"));
            while ((line = rd.readLine()) != null ) {
                sb.append(line);
            }
            response = sb.toString();
        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }finally{
            try {
                if(rd != null){
                    rd.close();
                }
                if(conn != null){
                    conn.disconnect();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return response;
    }
    //post表单请求
    public static String post(String url, Map<String, String> form){
        HttpURLConnection conn = null;
        PrintWriter pw = null ;
        BufferedReader rd = null ;
        StringBuilder out = new StringBuilder();
        StringBuilder sb = new StringBuilder();
        String line = null ;
        String response = null;
        for (String key : form.keySet()) {
            if(out.length()!=0){
                out.append("&");
            }
            out.append(key).append("=").append(form.get(key));
        }
        try {
            conn = (HttpURLConnection) new URL(url).openConnection();
            conn.setRequestMethod("POST");
            conn.setDoOutput(true);
            conn.setDoInput(true);
            conn.setReadTimeout(20000);
            conn.setConnectTimeout(20000);
            conn.setUseCaches(false);
            conn.connect();
            pw = new PrintWriter(conn.getOutputStream());
            pw.print(out.toString());
            pw.flush();
            rd  = new BufferedReader( new InputStreamReader(conn.getInputStream(), "UTF-8"));
            while ((line = rd.readLine()) != null ) {
                sb.append(line);
            }
            response = sb.toString();
        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }finally{
            try {
                if(pw != null){
                    pw.close();
                }
                if(rd != null){
                    rd.close();
                }
                if(conn != null){
                    conn.disconnect();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return response;
    }
    //post字符串请求
    public static String post(String url, String rawBody){
        HttpURLConnection conn = null;
        PrintWriter pw = null ;
        BufferedReader rd = null ;
        StringBuilder sb = new StringBuilder ();
        String line = null ;
        String response = null;
        try {
            conn = (HttpURLConnection) new URL(url).openConnection();
            conn.setRequestMethod("POST");
            conn.setDoOutput(true);
            conn.setDoInput(true);
            conn.setReadTimeout(20000);
            conn.setConnectTimeout(20000);
            conn.setUseCaches(false);
            conn.connect();
            pw = new PrintWriter(conn.getOutputStream());
            pw.print(rawBody);
            pw.flush();
            rd  = new BufferedReader( new InputStreamReader(conn.getInputStream(), "UTF-8"));
            while ((line = rd.readLine()) != null ) {
                sb.append(line);
            }
            response = sb.toString();
        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }finally{
            try {
                if(pw != null){
                    pw.close();
                }
                if(rd != null){
                    rd.close();
                }
                if(conn != null){
                    conn.disconnect();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return response;
    }



}