To do this, make a HEAD request and then check for a 404 error in your callback function; Listing 11 shows a sample callback.
要实现这种功能，生成一个HEAD请求，然后在回调函数中检查404错误；清单11给出了一个简单的回调函数。
Still, sometimes it's useful to know exactly what is available; you never know when creativity will strike and you'll need the HEAD request!
不过，有时确切地了解目前什么可用也是非常有用的；您永远不会知道何时创造力就会迸发或者何时需要 HEAD 请求！
What is the value in making a HEAD request?
生成HEAD请求的价值是什么呢？
Joao Leite, head of investment at Portugal's Banco Carregosa, said the request for aid was unlikely to lead to any significant reduction in the country's long-term debt yields.
葡萄牙的卡雷·戈萨银行的投资部主管若昂·雷特表示，请求援助是不可能导致任何国家的长期债券收益率显着减少的。
According to media reports, the head of General Motors, Rick Wagoner, has agreed to step down at the request of the White House, as part of a restructuring plan.
媒体报道说，通用汽车公司的总裁里克·瓦格纳已经同意，作为重组计划的一部分，他接受白宫提出的要他辞职的要求。
The child may respond to a teacher's request for quiet or control by looking away, putting his or her head down on the desk, orsimply ignoring the teacher.
孩子可能以冷漠和撇过去不看他们作为对老师要求的回应，低头对着桌子，直接无视老师的存在。
When you make a HEAD request like this, the server doesn't return an actual response as it would for a GET or POST request.
当您这样生成一个HEAD请求时，服务器并不会像对GET或POST请求一样返回一个真正的响应。
He rejected my request with an emphatic shake of his head.
他很坚决地摇头，拒绝了我的要求。
The HEAD request returns no HTTP message body but rather the request file's meta-information (size, etc.).
HEAD请求会返回空的HTTP消息体，但是会返回所请求文件的元数据信息(如，大小等)。
I also use the -i option to ask it to use an HTTP head request, getting just the response headers.
我还使用了- i选项来要求它使用HTTPHEAD请求，只获得响应头。
If the incoming request is either get or head, then the header in the response object is set and then forwards this request to the get method.
如果进入的请求是get或head，那么将设置响应对象的头部(header)，然后将此请求转发给get方法。
Listing 10 provides a simple callback function to output all the response headers from a head request.
清单10提供了一个简单的回调函数，用来输出从HEAD请求中获得的响应头的内容。
The first in our group to have a go, I was seated in a photographic booth and, after tilting my head at an appropriate Angle and lifting an eyebrow at the cameraman's request, he snapped away.
作为我们这个旅行团中第一个尝试的人，我被安排坐在一个拍照亭里，我按摄影师的要求将脑袋扭向了合适的角度并抬了抬眉头，他按动了快门儿。
Selects the request with the minimum seek time from the current head position.
选择从当前磁头位置所需寻道时间最短的请求。
He refused my request with a shake of his head.
他头一摇拒绝了我的要求。
Except when responding to a HEAD request, the server shouldinclude an entity containing an explanation of the error situation, and whether it is a temporary or permanent condition.
除非这是一个HEAD请求，否则服务器应当包含一个解释当前错误状态以及这个状况是临时的还是永久的解释信息实体。
But the material particle DNA sharp separation purification to the ultra centrifugal equipment (supercentrifuge, turned the head with appurtenance) to set a higher request.
而质粒dna的快速分离纯化又对超离心设备(超速离心机、转头和附属设备)提出了更高要求。
Simple HTTP request handler with GET and HEAD commands.
简单的HTTP请求处理方法，使用GET和HEAD命令。
Except when responding to a HEAD request, the server shouldinclude an entity containing an explanation of the error situation, and whether it is a temporary or permanent condition.
除非响应的是一个HEAD请求，否则服务器就应该返回一个解释当前错误状况的实体，以及这是临时的还是永久性的状况。 这些状态码适用于任何请求方法。
Digital display device or grinding head of electric spindle can be provided according to custom's request.
根据用户需求，可提供数显装置，电主轴磨头装置。
From above study, it would be concluded that the NC machining can meet the request of industrialization of femoral head prosthesis for alumina ceramic.
上述研究表明：从材料的制备与加工工艺、数控编程方法、加工成本等因素考虑，氧化铝陶瓷人工关节股骨头的数控加工技术能适应产业化的要求。
Village head: Inside the tunnel, there is a monster. Because you are the best warrior in our village, the villagers request you to fight the monster.
村长：因为隧道里面有怪物，我要征求勇士一名，而你是村里最厉害的勇士，所以村民就拜托你去消灭它。
The aesthetics and nutrient qualities of 19 common head cabbage materials were studied. The results showed that the aesthetics quality of the 19 materials all accorded with the breeding request.
研究了19份结球甘蓝材料的感官品质和营养品质，结果表明：19份材料的感官品质均符合育种要求。
The aesthetics and nutrient qualities of 19 common head cabbage materials were studied. The results showed that the aesthetics quality of the 19 materials all accorded with the breeding request.
研究了19份结球甘蓝材料的感官品质和营养品质，结果表明：19份材料的感官品质均符合育种要求。
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