# Java

## json 操作

JSONObject object = new JSONObject();   //new 空的JSONObject
JSONArray array = new JSONArray();        //new JSONArray

JSONArray res = dbpool.toJSONArray(sql);   
    
for (int i = 0; i < res.length(); i++) {
    JSONObject obj = res.getJSONObject(i);
    
    JSONArray arrays = obj.getJSONArray("arrays");
}

## Regex

String.matches("regex")
String testString = "ABCaaabcaac";
System.out.println("String.matches():\t"+testString.matches(".*aa.*"));

## Timestamp to Date

long currentTime = System.currentTimeMillis();  
Date date = new Date(currentTime);
SimpleDateFormat formatter = new SimpleDateFormat("yyyy年-MM月dd日-HH时mm分ss秒");
System.out.println(formatter.format(date));

## java-jwt
創建token

Algorithm al = Algorithm.HMAC256("secretkey");
    String token = JWT.create()
            .withIssuer("簽發者")
            .withSubject("用戶")
            .withClaim("userid", "string123")
            .withExpiresAt(new Date(System.currentTimeMillis()+360000))
            .sign(al);

解析token

Algorithm algorithm = Algorithm.HMAC256("emailauthority");
        JWTVerifier verifier = JWT.require(algorithm).build();
        DecodedJWT jwt = verifier.verify(key);

        long exp = jwt.getExpiresAt().getTime();
        String account = jwt.getClaim("userid").asString();

## Hashmap

HashMap<String,Integer> hashMap = new HashMap<>();

遍歷元素

Iterator iterator = hashMap.keySet().iterator();
        while (iterator.hasNext()){
            String key = (String)iterator.next();
            System.out.println(key+"="+hashMap.get(key));
        }

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