代理模式在图书馆系统中的应用-优快云博客

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        <script type=text/javascript charset=utf-8 src=../commons/CommonUtil.js ></script>
        <script type=text/javascript charset=utf-8>    
                //代理模式（proxy）：代理也是对象，他的目的就是为了节制（控制）对本体对象的访问
                
                var LibraryInterface = new BH.Interface('LibraryInterface' ,['addbook','findbook','checkoutbook','returnbook']);
                
                var Book = function(id , title , author){
                    this.id = id;
                    this.title = title ; 
                    this.author = author;
                };
                
                //图书馆(本体对象 , 实例化图书馆需要消耗很多的资源)
                var Library = function(books){
                    this.books = books;//{bookid : book}
                };
                Library.prototype = {
                    constructor:Library , 
                    addbook:function(book){
                        this.books[book.id] = book;//访问json用中括号
                    },
                    findbook:function(id){
                        if(this.books[id]){
                            return this.books[id];
                        }
                        return null;
                    },
                    checkoutbook:function(id){
                        //电脑登记..交押金
                        return this.findbook(id);
                    },
                    returnbook:function(book){
                        //电脑登记(...已还)
                        //计算费用(计算余额)
                        this.books[book.id] = book;
                    }
                };
                
                //图书馆的代理对象
                var LibraryProxy = function(books){
                    alert('产生代理对象，但是并没有产生真正的本体对象!');
                    this.books = books;
                    this.library = null; //定义一个空对象
                };
                LibraryProxy.prototype = {
                    constructor:LibraryProxy ,
                    initializeLibrary:function(){
                        if(this.library == null){
                            alert('真正的本体对象!');
                            this.library = new Library(this.books);
                        }
                    },
                    addbook:function(book){
                        this.initializeLibrary();
                        //实际上具体做事情的还是本体对象自己本身
                        this.library.addbook(book);
                    },
                    findbook:function(id){
                        this.initializeLibrary();
                        return this.library.findbook(id);
                    },
                    checkoutbook:function(id){
                        this.initializeLibrary();
                        return this.findbook(id);
                    },
                    returnbook:function(book){
                        this.initializeLibrary();
                        this.library.returnbook(book);
                    }
                };                
                
                //实例化的是代理对象：推迟本体对象实例化的时间，什么时候具体去做事情了，再去实例化它
                // hibernate： get(全查询出来)   load(返回代理对象)
                var proxy = new LibraryProxy({
                    "01":new Book('01','java','z3'),
                    "02":new Book('02','js','z4')
                });
                
                alert(proxy.findbook('01').title);
            
        </script>
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