cache.js

来自「ajax patterns 这是关于ajax设计模式方面的原代码」· JavaScript 代码 · 共 79 行

/*
    Copyright 2006 Christian Gross http://www.devspace.com
    From the book Ajax Patterns and Best Practices

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.
*/
var CacheController = {
    _cache : new Array(),
    prefetch : function( url) { },
    didNotFindETagError : function( url) { },    
    getCachedURL : function( url) {
        var func = function( status, statusText, responseText, responseXML) { }
        CacheController.getURL( url, func, true);
    },        
    getURL : function( url, complete, calledFromCache) {
        var asynchronous = new Asynchronous();
        asynchronous.openCallback = function( xmlhttp) {
            var obj = CacheController._cache[ url];
            if( obj != null) {
                xmlhttp.setRequestHeader( "If-None-Match", obj.ETag);
            }
        }
        asynchronous.userComplete = complete;
        asynchronous.complete = function( status, statusText, responseText, responseXML) {
            if( status == 200) {
                try {
                    var foundetag = this._xmlhttp.getResponseHeader( "ETag");
                    if( foundetag != null) {
                        CacheController._cache[ url] = {
                            ETag : foundetag,
                            Status : status,
                            StatusText : statusText,
                            ResponseText : responseText,
                            ResponseXML : responseXML
                        };
                    }
                    else {
                        CacheController.didNotFindETagError( url);
                    }
                }
                catch( exception) {
                    CacheController.didNotFindETagError( url);
                }
                this.userComplete( status, statusText, responseText, responseXML);
            }
            else if( status == 304) {
                var obj = CacheController._cache[ url];
                if( obj != null) {
                    this.userComplete( 304, obj.StatusText, 
                        obj.ResponseText, obj.ResponseXML);
                }
                else {
                    throw new Error( "Server indicated that this data is in the cache, but it does not seem to be");
                }
            }
            else {
                this.userComplete( status, statusText, responseText, responseXML);
            }
        }
        asynchronous.get( url);
        if( calledFromCache != true) {
            CacheController.prefetch( url);
        }
    }
}