简易JAVA爬虫练习，为新手总结的三种爬虫方法

这是想学习java爬虫的新手必经之路，也是最简单的几种JAVA爬虫爬取网页信息的方法，当然,这几种方法爬取的网页有限，对于需要登录的网页则还需进行更复杂的操作，这里就不做多余的解释，毕竟是写给新手的，希望对刚学习JAVA爬虫的人能有点帮助。

一、 通过urlconnection抓取信息：

步骤：
1.获取url
2.获取http请求
3.获取状态码
4.根据状态吗返回信息。

代码：
package com.soft.crawler;


import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.URL;
import sun.net.www.protocol.http.HttpURLConnection;


public class Crawler {
public static void main(String[] args){
String r;
//1.新建url对象，表示要访问的网页
try {
URL url = new URL("http://www.sina.com.cn");
//2.建立http连接,返回连接对象urlconnection
HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
//3.获取相应的http状态码，
int responseCode= urlConnection.getResponseCode();
//4.如果获取成功，从URLconnection对象获取输入流来获取请求网页的源代码
if(responseCode == 200){
BufferedReader reader = new BufferedReader(new InputStreamReader(urlConnection.getInputStream(), "utf-8"));
while((r=reader.readLine())!=null){
System.out.println(r);
}
}else{
System.out.println("获取不到源代码 ，服务器响应代码为："+responseCode);
}
} catch (Exception e) {
System.out.println("获取不到网页源码："+e);
}
}
}

二、通过httpclient抓取信息：

步骤：
//创建一个客户端，类似打开一个浏览器


HttpClient httpClient = new HttpClient();


//创建一个get方法，类似在浏览器中输入一个地址，path则为URL的值


GetMethod getMethod = new GetMethod(path);


//获得响应的状态码


int statusCode = httpClient.executeMethod(getMethod);


//得到返回的类容


String resoult = getMethod.gerResponseBodyAsString();


//释放资源


getMethod.releaseConnection();





代码：

import java.io.FileWriter;
import java.io.IOException;
import java.util.Scanner;

import org.apache.commons.httpclient.HttpClient;
import org.apache.commons.httpclient.HttpException;
import org.apache.commons.httpclient.HttpStatus;
import org.apache.commons.httpclient.methods.GetMethod;


public class Crawler{
private static HttpClient httpClient = new HttpClient();
static GetMethod getmethod;
public static boolean downloadPage(String path) throws HttpException,
IOException {
getmethod = new GetMethod(path);
//获得响应状态码
int statusCode = httpClient.executeMethod(getmethod);
if(statusCode == HttpStatus.SC_OK){
System.out.println("response="+getmethod.getResponseBodyAsString());
//写入本地文件
FileWriter fwrite = new FileWriter("hello.txt");
String pageString = getmethod.getResponseBodyAsString();
getmethod.releaseConnection();
fwrite.write(pageString,0,pageString.length());
fwrite.flush();
//关闭文件
fwrite.close();
//释放资源
return true;
}
return false;
}




/**
* 测试代码
*/
public static void main(String[] args) {
// 抓取制指定网页，并将其输出
try {
Scanner in = new Scanner(System.in);
System.out.println("Input the URL of the page you want to get:");
String path = in.next();
System.out.println("program start!");
Crawler.downloadPage(path);
System.out.println("Program end!");
} catch (HttpException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
}

三，通过jsoup获取网页信息:

package com.soft.test;


import java.io.File;
import java.io.IOException;


import org.jsoup.Jsoup;
import org.jsoup.nodes.Document;
import org.jsoup.nodes.Element;
import org.jsoup.select.Elements;


public class spider {
public static void main(String[] args) throws IOException{
String url = "http://www.baidu.com";
Document document = Jsoup.connect(url).timeout(3000).get();


//通过Document的select方法获取属性结点集合
Elements elements = document.select("a");
//得到节点的第一个对象
//Element element = elements.get(0);
System.out.println(element);

}

}