JSON取值前判断

　　public static void main(String[] args)throws Exception{

　　String jsonStr1="{\"access_token\":\"OezXcEiiBSKSxW0eoylIeIVb08lFhyeFsq6cUJJNo8XYLoJjqYARJOZUrnqhfvnyMKOSjz5SHPHGUmt6f09_762MWQ0HLnZtffDPyD2A6TgCqWlZAEsHLhIaaQVYx1lywxOWQTrr7rX13i_w1INGnw\",\"expires_in\":7200,\"openid\":\"owYTUs68SXYX83wBvm_uN4Ya****\",\"scope\":\"snsapi_base\"}";

　　String jsonStr2="{\"access_token\":\"OezXcEiiBSKSxW0eoylIeIVb08lFhyeFsq6cUJJNo8XYLoJjqYARJOZUrnqhfvnyMKOSjz5SHPHGUmt6f09_762MWQ0HLnZtffDPyD2A6TgCqWlZAEsHLhIaaQVYx1lywxOWQTrr7rX13i_w1INGnw\",\"expires_in\":7200,\"refresh_token\":\"OezXcEiiBSKSxW0eoylIeIVb08lFhyeFsq6cUJJNo8XYLoJjqYARJOZUrnqhfvnyuq9ojibRxolf9ElS7PSM0Kz1OTNlJ8ZKJl2BfbPi0LA-nQ9uNVUE8ujLFsdCeP79_L9FmIYcmHLXWXnl-fUsVg\",\"openid\":\"owYTUs68SXYX83wBvm_uN4Y****\",\"scope\":\"snsapi_base\"}";

　　JSONObject json1=JSONObject.fromObject(jsonStr1);

　　JSONObject json2=JSONObject.fromObject(jsonStr2);

　　String refresh_token_1=null;

　　String refresh_token_2=null;

　　if(json1.containsKey("refresh_token")){

　　refresh_token_1=json1.getString("refresh_token");

　　}

　　if(json2.containsKey("refresh_token")){

　　refresh_token_2=json2.getString("refresh_token");

　　}

　　System.out.println(refresh_token_1);

　　System.out.println(refresh_token_2);

　　}

　　null

　　OezXcEiiBSKSxW0eoylIeIVb08lFhyeFsq6cUJJNo8XYLoJjqYARJOZUrnqhfvnyuq9ojibRxolf9ElS7PSM0Kz1OTNlJ8ZKJl2BfbPi0LA-nQ9uNVUE8ujLFsdCeP79_L9FmIYcmHLXWXnl-fUsVg