代码
import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.Reader;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLConnection;
import java.nio.charset.Charset;
public class ReadUrlTwo {
/**
* 打印 URLConnection 头部信息
* URL和URLConnection这两个类最大的不同在于:
* URLConnection提供了对HTTP首部的访问；
* URLConnection可以配置发送给服务器的请求参数；
* URLConnection除了读取服务器数据外，还可以向服务器写入数据；
*/
public static void printConnection(URLConnection connection){
System.out.println("Content-Type: " + connection.getContentType());
System.out.println("Content-Length: " + connection.getContentLength());
System.out.println("Content-LengthLong: " + connection.getContentLengthLong());
System.out.println("Content-encoding: " + connection.getContentEncoding());
System.out.println("Date: " + connection.getDate());
System.out.println("Expires: " + connection.getExpiration());
System.out.println("Last-modified: " + connection.getLastModified());
}
public static void printHeader(URLConnection connection) {
for (int i = 1; ; i++) {
String header = connection.getHeaderField(i);
if (header == null) {
break;
}
System.out.println(connection.getHeaderFieldKey(i) + ": " + header);
}
}
// 直接输出 char 类型
public static void get(URLConnection connection) {
try {
ReadUrlTwo.printHeader(connection);
InputStream in = connection.getInputStream();
//将InputStream串链到一个Reader
Reader reader = new InputStreamReader(in);
int c;
while ((c = reader.read())!= -1) {
System.out.print((char)c);
}
} catch (Exception e) {
e.printStackTrace();
}
}
public static void getString(URLConnection connection) {
try {
InputStream inputStream=connection.getInputStream();
byte[] data=new byte[1024];
StringBuffer sb = new StringBuffer();
int length = 0;
while ((length = inputStream.read(data)) != -1){
String s = new String(data, Charset.forName("utf-8"));
sb.append(s);
}
String message = sb.toString();
System.out.println(message);
} catch (Exception e) {
e.printStackTrace();
}
}
public static void main(String[] args) {
try {
URL url = new URL("http://www.baidu.com/");
URLConnection connection = url.openConnection();
System.out.println("print HTTP Header =====>> ");
ReadUrlTwo.printConnection(connection);
System.out.println("print HTTP Header Field ======>> ");
ReadUrlTwo.printHeader(connection);
// ReadUrl.get(connection);
ReadUrlTwo.getString(connection);
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (Exception e) {
e.printStackTrace();
}
}
}这个程序被static修饰的变量和方法可以被直接引用
为什么要用static关键字？
答：有一些频繁使用的东西，如果你每次使用都重新new一下，那么这个开销可能会很高，如果使用static，一直放在内存中，那么想用就直接用，而不需要重新new一块空间初始化数据。那么static就是为了实现一个系统的缓存作用的，其生命周期直到应用程序退出结束。
相关方法解释
printConnection是与服务器建立连接访问读取HTTP首部的数据printHeader是返回整个首部字段的字段名get就是发送GET请求，调用printHeader方法，connection获得的输入流将指向in使用方法getInputStream()获得的那个输出流，再通过InputStreamReader读取字节getString就是将输入流指向输出流，创建字节数组作为缓冲区，构造字符串sb，定义长度为0，当长度与读取出来的数据一致并不为-1时，则将数据以UTF-8的形式编码，sb添加了一个s,最后新建一个字符串返回该对象的字符串，打印结果
运行结果
print HTTP Header =====>>
Content-Type: text/html
Content-Length: 2381
Content-LengthLong: 2381
Content-encoding: null
Date: 1585235629000
Expires: 0
Last-modified: 0
print HTTP Header Field ======>>
Content-Length: 2381
Content-Type: text/html
Server: bfe
Date: Thu, 26 Mar 2020 15:13:49 GMT
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