map.keySet()获取map全部的key值

public static String getUrlWithQueryString(String url, Map<String, String> params) {
if (params == null) {
return url;
} StringBuilder builder = new StringBuilder(url);
if (url.contains("?")) {
builder.append("&");
} else {
builder.append("?");
} int i = 0;
for (String key : params.keySet()) {
String value = params.get(key);
if (value == null) { // 过滤空的key
continue;
} if (i != 0) {
builder.append('&');
} builder.append(key);
builder.append('=');
builder.append(encode(value)); i++;
} return builder.toString();
}