用Java抓取CSDN主页上的图片

一，步骤一：获取网页源码

1，定义要爬取的页面的URL对象

//定义即将访问的链接
String url="http://www.csdn.net";
//获取CSDN的URL对象
URL realURL = new URL(url);
2，获得这个链接的一个连接对象
URLConnection connection = realURL.openConnection();

        3，开始连接
connection.connect();
4，将连接的输入流转化成BufferedReader输入流，通过BufferedReader对象存放到一个String对象中
in = new BufferedReader(new InputStreamReader(connection.getInputStream()));
String line="";
while((line=in.readLine())!=null){
result+=line+"\n";
}二，步骤二：正则匹配，存储图片
1，找出正则表达式的样板

Pattern pattern = Pattern.compile("<img \\S+\\ssrc=\"(.+?)\"");
2，匹配对象
Matcher matcher = pattern.matcher(result);
3，实例化文件输出流
imgFile= new FileOutputStream("D:\\CSDN"+i+".png");
4，获得图片链接的缓冲流

URL imgURL = new URL(img);
URLConnection imgConnection = imgURL.openConnection();
imgConnection.connect();
bufferedImage = (BufferedInputStream) new BufferedInputStream(imgConnection.getInputStream());

5，将缓冲流写入文件中

while((size=bufferedImage.read(buf))!=-1){
<span style="white-space:pre"> </span>imgFile.write(buf, 0, size);
}

6，将输入输出流关闭

in.close();
imgFile.close();
bufferedImage.close();

程序的完整源码：
import java.io.*;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLConnection;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class CrawOne {

public static void main(String[] args) throws IOException {
// TODO Auto-generated method stub
//定义即将访问的链接
String url="http://www.csdn.net";
//定义一个用来存储的字符串
String result="";
//用于存储网页源代码
BufferedReader in = null;
//用于存储图片链接
String img=null;
int i=0;
int size=0;
//定义每一次读取缓冲区的最大值
int BUFFER_SIZE = 1024;
byte[] buf = new byte[BUFFER_SIZE];
//图片文件输出流
FileOutputStream imgFile=null;
//缓冲输入流
BufferedInputStream bufferedImage =null;
try {
//获取CSDN的URL对象
URL realURL = new URL(url);
//获得这个链接的一个连接对象
URLConnection connection = realURL.openConnection();
//开始连接
connection.connect();
//将连接的输入流转化成BufferedReader输入流
in = new BufferedReader(new InputStreamReader(connection.getInputStream()));
String line="";
while((line=in.readLine())!=null){
result+=line+"\n";
}

//找出正则表达式的样板
Pattern pattern = Pattern.compile("<img \\S+\\ssrc=\"(.+?)\"");

//匹配对象
Matcher matcher = pattern.matcher(result);

while(matcher.find()){
System.out.println("find one");
//获得匹配的值，由于只定义了一个群组，即正则表达式中打括号的组数，所以是group（1），group（0）表示的是整个匹配
img = matcher.group(1);
//实例化文件输出流
imgFile= new FileOutputStream("D:\\CSDN"+i+".png");
i++;
//获得图片链接的缓冲流
URL imgURL = new URL(img); URLConnection imgConnection = imgURL.openConnection(); imgConnection.connect(); bufferedImage = (BufferedInputStream) new BufferedInputStream(imgConnection.getInputStream());
//将缓冲流写入文件中
while((size=bufferedImage.read(buf))!=-1){
imgFile.write(buf, 0, size);
}

}

} catch (MalformedURLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}finally {
if (in!=null) {
//将输入输出流关闭
in.close();
imgFile.close();
bufferedImage.close();
}
}
System.out.println("Get some picture.");
}

}