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<td width="90%"><font size="4" face="Verdana, Arial, Helvetica"><b>HTTP 方法</b></font></td><td width="200" align="right"><font size="1" face="Verdana, Arial, Helvetica"><nobr> 第 1 页(共7 页)</nobr></font></td>
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<p>HTTP 方法指出了客户机发给服务器的 HTTP 请求的目的。4 个常见的 HTTP 方法是 <code>GET</code>、<code>POST</code>、<code>PUT</code> 和 <code>HEAD</code>。让我们来看一下这些方法的特性,及它们是如何触发的。</p>
<p>
<b><code>GET</code> 方法</b>
<br>
<code>GET</code> 方法用于从服务器获取资源(比如图像或 HTML 页面),该资源是在请求 URL 中指定的。当用户在浏览器的位置字段键入请求 URL,或者单击超链接时,会触发 <code>GET</code> 方法。如果使用标签,方法属性可以被指定为“<code>GET</code>”,从而导致浏览器发送 <code>GET</code> 请求。即使没有指定任何方法属性,默认情况下,浏览器也使用 <code>GET</code> 方法。</p>
<p>通过把查询字符串追加到请求 URL,我们可以传入请求参数,查询字符串是一组“名-值”对,由“&”字符隔开。例如:</p>
<pre>
<code style="font-family: Courier New, Courier, monospace; font-size: 12">http://www.testserver.com/myapp/testservlet?studname=Tom&studno=123</code>
</pre>
<p>这里,我们已经传入参数 <code>studname</code> 和 <code>studno</code>,它们分别具有值“Tom” 和 “123”。因为在 URL 内部,使用 <code>GET</code> 方法传递的数据是可见的,所以不建议以这种方式发送敏感数据。 <code>GET</code> 方法的其他限制是,它只能传递文本数据,并且不能超过 255 个字符。</p>
<p>
<b><code>POST</code> 方法</b>
<br>
<code>POST</code> 方法的目的是“投递”或发送信息给服务器。可以把不限量的数据作为 <code>POST</code> 请求的一部分发送,并且数据的类型可以是二进制或文本。</p>
<p>该方法通常用于发送大容量数据,比如上传文件或更新数据库。<code><form></code> 标签的方法属性可以被指定成“<code>POST</code>”,导致浏览器发送 <code>POST</code> 请求给服务器。</p>
<p>因为请求参数是作为请求体的一部分发送,所以它不可作为请求 URL 的一部分出现,对于 <code>GET</code> 方法,也是这样。</p>
<p>
<b><code>PUT</code> 方法</b>
<br>
<code>PUT</code> 方法在服务器上添加资源,主要用于发布页面。它类似于 <code>POST</code> 请求,因为两者都是对准服务器端资源。但区别在于,<code>POST</code> 方法导致服务器上的资源处理请求,而 <code>PUT</code> 方法把请求数据与服务器上的 URL 关联起来。</p>
<p>
<code><form></code> 标签的属性可以被指定成“<code>PUT</code>”,导致浏览器发送 <code>PUT</code> 请求给服务器。</p>
<p>
<b><code>HEAD</code> 方法</b>
<br>
<code>HEAD</code> 方法用于获取服务器上特定资源的头。通常,您将用 <code>HEAD</code> 来获取某个资源的最后修改时间或内容类型。它可以节省带宽,因为有关资源的元信息是在没有传输资源本身下获得的。</p>
<p>
<code><form></code> 标签的方法属性可以被指定为“<code>HEAD</code>” ,导致浏览器发送 <code>HEAD</code> 请求给服务器。</p>
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