URLConnection类的使用和总结

URLConnection类

URLConnection类概述

The abstract class URLConnection is the superclass of all classes that represent a communications link between the application and a URL. Instances of this class can be used both to read from and to write to the resource referenced by the URL. In general, creating a connection to a URL is a multistep process:

抽象类URLConnection 是所有应用程序和 URL 之间的通信链接的超类。此类的实例可以读取和写入被url引用的资源。通常，创建一个连接需要如下几个步骤：

1、The connection object is created by invoking the openConnection method on a URL.
——-通过在 URL 上调用 openConnection 方法创建连接对象。
2、The setup parameters and general request properties are manipulated.
——-处理设置参数和一般请求属性。
3、The actual connection to the remote object is made, using the connect method.
——-使用 connect 方法建立到远程对象的实际连接。
4、The remote object becomes available. The header fields and the contents of the remote object can be accessed.
——-远程对象变为可用。远程对象的头字段和内容变为可访问。

The setup parameters are modified using the following methods:
——-设置参数方法如下：
setAllowUserInteraction
setDoInput
setDoOutput
setIfModifiedSince
setUseCaches
and the general request properties are modified using the method:
通常设置request 属性使用如下方法
setRequestProperty

Default values for the AllowUserInteraction and UseCaches parameters can be set using the methods
对AllowUserInteraction 和UseCaches 设置默认值， 可以使用如下方法：
setDefaultAllowUserInteraction and setDefaultUseCaches.

Each of the above set methods has a corresponding get method to retrieve the value of the parameter or general request property. The specific parameters and general request properties that are applicable are protocol specific.
上面每一个set方法都有一个相应的get方法来取参数的值或者request的属性。用的特定参数和通用请求属性使用专用的协议。

The following methods are used to access the header fields and the contents after the connection is made to the remote object:
在链接远程成功之后，用下面的方法用来访问header和content
getContent
getHeaderField
getInputStream
getOutputStream
Certain header fields are accessed frequently. The methods:

getContentEncoding
getContentLength
getContentType
getDate
getExpiration
getLastModifed