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);
}

运行结果:
null
OezXcEiiBSKSxW0eoylIeIVb08lFhyeFsq6cUJJNo8XYLoJjqYARJOZUrnqhfvnyuq9ojibRxolf9ElS7PSM0Kz1OTNlJ8ZKJl2BfbPi0LA-nQ9uNVUE8ujLFsdCeP79_L9FmIYcmHLXWXnl-fUsVg