Implementation method of JS front-end cache and introduction to the characteristics of Cookie

In the front-end browser, some data (such as the data in the data dictionary) can be retrieved and saved in the js object during the first request, so that you do not need to request the server every time when needed in the future. . For pages that heavily use data dictionaries to populate drop-down boxes, this approach can greatly reduce server visits. This method works especially well with frames using iframes.

This article mainly introduces the method of JS to implement front-end caching in detail. It has certain reference value. Interested friends can refer to it. I hope it can help everyone.

Specific implementation ideas and methods:

Create a cache.js file:

1. Front-end page, define which data needs to be obtained from the front-end cache at one time, and define an object To save this data:

/**
 * 定义需要在用户登录的时候获取到本地的数据字典类别
 */
var clsCodes = {clsCodes :
    [BOOL,
     STATUS,
     USER_TYPE,
     REPORT_STATUS
   ]
};
 
/**
 * 获取数据字典到本地
 */
var dicts;

2. On the front-end page, define a function to call the back-end interface to obtain the data, and then save it to the local cache object (dicts).

function getDicts() {
  $.post(getContextPath() + /api/sys/getDictList,
      clsCodes,
      function(resultBean, status, xhRequest) {
        if (resultBean.data != undefined) {
          dicts = resultBean.data;
        }
      }, 
      'json');
}

Call this method to obtain the data at once and cache it when the main page is loaded. In this way, if you need the same data in the future, you can get it directly from the local object dicts.

Backend Controller:

3. Define an interface to query the database (or query the server cache, as in the following example) according to the front-end request to obtain data and return it to the front-end:

/**
 * 根据多个分类编号获取多个字典集合
 * @param clsCodes
 * @return {{clsCode : {code1:name1,code2:name2...}}, ...}
 */
@SuppressWarnings({ unchecked, rawtypes })
@ResponseBody
@RequestMapping(getDictList)
public ResultBean getDictList(@RequestParam(value = clsCodes[], required = true) String[] clsCodes) {
  ResultBean rb = new ResultBean();
   
  Map<string, string="">> dictCache = (Map<string, string="">>) CacheManager.getInstance().get(CacheConstants.DICT);
  Map dictMap = new LinkedHashMap<>(); //使用LinkedHashMap保证顺序
 
  if(dictCache != null){
    for(String clsCode: clsCodes){
      dictMap.put(clsCode, dictCache.get(clsCode));
    }
  }else{
    rb.setMessage(缓存中拿不到字典信息！);
    rb.setSuccess(false);
  }
 
  rb.setData(dictMap);
  return rb;
}</string,></string,>

1. Characteristics of Cookie

1) The size of the cookie is limited. The cookie size is limited to 4KB and cannot accept big data like large files or emails.

2) As long as there is a request involving cookies, cookies will be sent back and forth between the server and the browser (this explains why local files cannot test cookies). Moreover, the cookie data is always carried in the http request from the same origin (even if it is not needed), which is also an important reason why the cookie cannot be too large. Orthodox cookie distribution is achieved by extending the HTTP protocol. The server adds a special line of instructions to the HTTP response header to prompt the browser to generate the corresponding cookie according to the instructions.

3) Every time a user requests server data, cookies will be sent to the server along with these requests. Server scripting languages ​​such as PHP can process the data sent by cookies, which can be said to be very convenient. Of course, the front end can also generate cookies. Using js to operate cookies is quite cumbersome. The browser only provides an object such as document.cookie, and assigning and obtaining cookies is troublesome. In PHP, we can set cookies through setcookie() and obtain cookies through the super-global array $_COOKIE.

The content of cookie mainly includes: name, value, expiration time, path and domain. The path and domain together form the scope of the cookie. If the expiration time is not set, it means that the lifetime of this cookie is during the browser session. When the browser window is closed, the cookie disappears. This type of cookie that lasts for the duration of the browser session is called a session cookie. Session cookies are generally not stored on the hard disk but in memory. Of course, this behavior is not specified by the specification. If an expiration time is set, the browser will save the cookies to the hard disk. If you close and open the browser again, these cookies will still be valid until the set expiration time is exceeded. Cookies stored on the hard drive can be shared between different browser processes, such as two IE windows. Different browsers have different ways of handling cookies stored in memory.

Related recommendations:

Use JS to implement front-end caching

The above is the detailed content of Implementation method of JS front-end cache and introduction to the characteristics of Cookie. For more information, please follow other related articles on the PHP Chinese website!