网络编程之URL和URLConnection

网络编程之URL和URLConnection

介绍

URL和URLConnection类是完成http网络请求时所用到的两个对象

The java.net package contains two interesting classes: The URL class and the URLConnection class.
these classes can be used to create client connections to web servers (HTTP servers).

URL

java中URL类代表了日常所使用的url(统一资源定位符),我们当然也可以使用字符串来代替url,
不过java是面向对象编程语言因此使用URL对象来表示。

Class URL represents a Uniform Resource Locator, a pointer to a "resource" on the World Wide Web.
A resource can be something as simple as a file or a directory, or it can be a reference to
a more complicated object,such as a query to a database or to a search engine.

/**
* URL类中定义了很多方法,能够操作大部分url里面的内容,URL类定义和url语法格式一致。所以操作起来也很方便。
*
* 最常用的两个方法
*     URL(String url);构造方法 URLConnection
*     openConnection();获得URLConnection连接对象
*/
// 初始化URL对象
URL url = new URL("url 地址");

// 根据URL对象获得连接对象
URLConnection connection = url.openConnection();

URLConnection

URLConnection表示一个连接对象,通过这个对象我们可以做很多事情(获得响应信息)。
URLConnection其实是一个抽象类,其主要实现有HttpURLConnection和JarURLConnection类,
绝大多数情况下我们是使用HttpURLConnection类的。

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.

abstract public class HttpURLConnection extends URLConnection {

public void setRequestMethod(String method) throws ProtocolException {}//重点掌握

public int getResponseCode() throws IOException {}//重点掌握

//Returns an input stream that reads from this open connection.
//设置输入流就是为了获得请求体里的数据
public InputStream getInputStream() throws IOException {}//重点掌握

//Returns an output stream that writes to this connection.
//获得这个输出流其实就是为了向请求体里增加数据
public OutputStream getOutputStream() throws IOException {}//重点掌握

//设置从HttpURLConnection对象能否获得输入和输出流
public void setDoInput(boolean doinput) {}//默认为true(因为很常用所以设置为true),重点掌握
//如果是post方法时,就一定要设置为true
public void setDoOutput(boolean dooutput) {}//默认为false,重点掌握

//Sets the general request property. If a property with the key already
//exists, overwrite its value with the new value.
//就是设置请求头信息
public void setRequestProperty(String key, String value) {}

public Map<String,List<String>> getRequestProperties() {}

}

我们可以使用URL和URLConnection来完成http请求组件工具,具体参考之前写的一篇文章

参考