HTML5 Web 客户端五种离线存储方式汇总

zjnig的信息仓库 2014-12-22

最近折腾HTML5游戏需要离线存储功能,便把目前可用的几种HTML5存储方式研究了下,基于HT for Web写了个综合的实例,分别利用了Cookie、WebStorage、IndexedDB以及FileSystem四种本地离线存储方式,对燃气监控系统的表计位置、朝向、开关以及表值等信息做了CURD的存取操作。

HTML5的存储还有一种Web SQL Database方式,虽然还有浏览器支持,是唯一的关系数据库结构的存储,但W3C以及停止对其的维护和发展,所以这里我们也不再对其进行介绍:Beware. This specification is no longer in active maintenance and the Web Applications Working Group does not intend to maintain it further.

HTML5 Web 客户端五种离线存储方式汇总

整个示例主要就是将HT for WebDataModel数据模型信息进行序列化和反序列化,这个过程很简单通过dataModel.serialize()将模型序列化成JSON字符串,通过dataModel.deserialize(jsonString)将JSON字符串内存反序列化出模型信息,而存储主要就是主要就是针对JSON字符串进行操作。

先介绍最简单的存储方式LocalStorage,代码如下,几乎不用介绍就是Key-Value的简单键值对存储结构,Web Storage除了localStorage的持久性存储外,还有针对本次回话的sessionStorage方式,一般情况下localStorage较为常用,更多可参考 http://www.w3.org/TR/webstorage/

function save(dataModel){
    var value = dataModel.serialize();
    window.localStorage['DataModel'] = value;
    window.localStorage['DataCount'] = dataModel.size();
    console.log(dataModel.size() + ' datas are saved');
    return value;
}
function restore(dataModel){  
    var value = window.localStorage['DataModel'];
    if(value){
        dataModel.deserialize(value);
        console.log(window.localStorage['DataCount'] + ' datas are restored');
        return value;
    }    
    return '';
}
function clear(){
    if(window.localStorage['DataModel']){
        console.log(window.localStorage['DataCount'] + ' datas are cleared');
        delete window.localStorage['DataModel'];
        delete window.localStorage['DataCount'];         
    }   
}

 最古老的存储方式为Cookie,本例中我只能保存一个图元的信息,这种存储方式存储内容很有限,只适合做简单信息存储,存取接口设计得极其反人类,为了介绍HTML5存储方案的完整性我顺便把他给列上:

function getCookieValue(name) {
    if (document.cookie.length > 0) {
        var start = document.cookie.indexOf(name + "=");
        if (start !== -1) {
            start = start + name.length + 1;
            var end = document.cookie.indexOf(";", start);
            if (end === -1){
                end = document.cookie.length;
            }
            return unescape(document.cookie.substring(start, end));
        }
    }
    return '';
}
function save(dataModel) {
    var value = dataModel.serialize();
    document.cookie = 'DataModel=' + escape(value);
    document.cookie = 'DataCount=' + dataModel.size();    
    console.log(dataModel.size() + ' datas are saved');
    return value;
}
function restore(dataModel){  
    var value = getCookieValue('DataModel');
    if(value){
        dataModel.deserialize(value);
        console.log(getCookieValue('DataCount') + ' datas are restored');
        return value;
    }    
    return '';
}
function clear() {
    if(getCookieValue('DataModel')){
        console.log(getCookieValue('DataCount') + ' datas are cleared');
        document.cookie = "DataModel=; expires=Thu, 01 Jan 1970 00:00:00 UTC";
        document.cookie = "DataCount=; expires=Thu, 01 Jan 1970 00:00:00 UTC";   
    }
}

 如今比较实用强大的存储方式为Indexed Database API,IndexedDB可以存储结构对象,可构建key和index的索引方式查找,目前各浏览器的已经逐渐支持IndexedDB的存储方式,其使用代码如下,需注意IndexedDB的很多操作接口类似NodeJS的异步回调方式,特别是查询时连cursor的continue都是异步再次回调onsuccess函数的操作方式,因此和NodeJS一样使用上不如同步的代码容易。

request = indexedDB.open("DataModel");
request.onupgradeneeded = function() {  
    db = request.result;
    var store = db.createObjectStore("meters", {keyPath: "id"});
    store.createIndex("by_tag", "tag", {unique: true});
    store.createIndex("by_name", "name");  
};
request.onsuccess = function() {
    db = request.result;
};

function save(dataModel){
    var tx = db.transaction("meters", "readwrite");
    var store = tx.objectStore("meters");
    dataModel.each(function(data){
        store.put({
            id: data.getId(),
            tag: data.getTag(),
            name: data.getName(),
            meterValue: data.a('meter.value'),
            meterAngle: data.a('meter.angle'),
            p3: data.p3(),
            r3: data.r3(),
            s3: data.s3()
        });    
    });   
    tx.oncomplete = function() {
        console.log(dataModel.size() + ' datas are saved');
    };    
    return dataModel.serialize();
}
function restore(dataModel){     
    var tx = db.transaction("meters", "readonly");
    var store = tx.objectStore("meters");
    var req = store.openCursor();  
    var nodes = [];
    req.onsuccess = function() {        
        var res = req.result;
        if(res){
            var value = res.value;
            var node = createNode();
            node.setId(value.id);
            node.setTag(value.tag);
            node.setName(value.name);                        
            node.a({
                'meter.value': value.meterValue,
                'meter.angle': value.meterAngle
            });
            node.p3(value.p3);                    
            node.r3(value.r3);
            node.s3(value.s3);
            nodes.push(node);             
            res.continue();
        }else{
            if(nodes.length){
                dataModel.clear();
                nodes.forEach(function(node){
                    dataModel.add(node);                         
                });
                console.log(dataModel.size() + ' datas are restored');
            }             
        }       
    };    
    return '';
}
function clear(){
    var tx = db.transaction("meters", "readwrite");
    var store = tx.objectStore("meters");
    var req = store.openCursor();
    var count = 0;
    req.onsuccess = function(event) {        
        var res = event.target.result;
        if(res){
            store.delete(res.value.id);
            res.continue();
            count++;
        }else{
            console.log(count + ' datas are cleared');
        }         
    };

}

 最后是FileSystem API相当于操作本地文件的存储方式,目前支持浏览器不多,其接口标准也在发展制定变化中,例如在我写这个代码时大部分文献使用的webkitStorageInfo已被navigator.webkitPersistentStorage和navigator.webkitTemporaryStorage替代,存储的文件可通过filesystem:http://www.hightopo.com/persistent/meters.txt’的URL方式在chrome浏览器中查找到,甚至可通过filesystem:http://www.hightopo.com/persistent/类似目录的访问,因此也可以动态生成图片到本地文件,然后通过filesystem:http:***的URL方式直接赋值给img的html元素的src访问,因此本地存储打开了一扇新的门,相信以后会冒出更多稀奇古怪的奇葩应用。

navigator.webkitPersistentStorage.queryUsageAndQuota(function (usage, quota) {
        console.log('PERSISTENT: ' + usage + '/' + quota + ' - ' + usage / quota + '%');
    }
);
navigator.webkitPersistentStorage.requestQuota(2 * 1024 * 1024,
    function (grantedBytes) {
        window.webkitRequestFileSystem(window.PERSISTENT, grantedBytes,
            function (fs) {
                window.fs = fs;
            });
    }
);
function save(dataModel) {
    var value = dataModel.serialize();
    fs.root.getFile('meters.txt', {create: true}, function (fileEntry) {
        console.log(fileEntry.toURL());
        fileEntry.createWriter(function (fileWriter) {
            fileWriter.onwriteend = function () {
                console.log(dataModel.size() + ' datas are saved');
            };
            var blob = new Blob([value], {type: 'text/plain'});
            fileWriter.write(blob);
        });
    });
    return value;
}
function restore(dataModel) {
    fs.root.getFile('meters.txt', {}, function (fileEntry) {
        fileEntry.file(function (file) {
            var reader = new FileReader();
            reader.onloadend = function (e) {
                dataModel.clear();
                dataModel.deserialize(reader.result);
                console.log(dataModel.size() + ' datas are restored');
            };
            reader.readAsText(file);
        });
    });
    return '';
}
function clear() {
    fs.root.getFile('meters.txt', {create: false}, function(fileEntry) {
        fileEntry.remove(function() {
            console.log(fileEntry.toURL() + ' is removed');
        });
    });    
}

 HTML5 Web 客户端五种离线存储方式汇总

Browser-Side的存储方式还在快速的发展中,其实除了以上几种外还有Application Cache,相信将来还会有新秀出现,虽然“云”是大趋势,但客户端并非要走极端的“瘦”方案,这么多年冒出了这么多客户端存储方式,说明让客户端更强大的市场需求是强烈的,当然目前动荡阶段苦逼的是客户端程序员,除了要适配Mouse和Touch,还要适配各种屏,如今还得考虑适配各种存储,希望本文能在大家选型客户端存储方案时有点帮助,最后上段基于HT for Web操作HTML5存储示例的视频效果:http://v.youku.com/v_show/id_XODUzODU2MTY0.html
<iframe src="http://player.youku.com/embed/XODUzODU2MTY0" frameborder="0" width="510" height="498"></iframe>

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