根据Url获取json，再根据key获取值以及json字符串转json对象

//如果你得Url能返回json。可以使用以下代码。

/**
* 根据url获得json
* @param url
* @return
*/
public static String loadJson(String url)  {
StringBuilder json = new StringBuilder();

try {
URL urlObject = new URL(url);
URLConnection uc  = urlObject.openConnection();
BufferedReader in = new BufferedReader(new InputStreamReader(uc.getInputStream()));
String inputLine = null;
while((inputLine = in.readLine())!=null){
json.append(inputLine);
}
in.close();
}catch (MalformedURLException e)
{
e.printStackTrace();
}catch (IOException e)
{
e.printStackTrace();
}
return json.toString();
}

/**
* 将字符串json转换为json格式，并根据key取出value
* @param url
* @return
*/
public static String findKeytoValueFromJson(String url){
String getJosn = loadJson(url);
String j1 = "\"";
String jj = "\\";
StringBuilder ss = new StringBuilder();

for (int i = 0; i < getJosn.length(); i++) {
if (j1.equals(String.valueOf(getJosn.charAt(i)))) {
ss = ss.append(new StringBuilder(jj));
}
ss.append(getJosn.charAt(i));
}
String jsonStr = ss.toString();
jsonStr ="["+getJosn+"]";
JSONArray jkfJson =  JSONArray.fromObject(jsonStr);
String  accessToken  = jkfJson.getJSONObject(0).get("access_token").toString();
return accessToken;
}