python爬虫初步-与java爬虫的比较

相比较java来说,python的http库类更佳丰富,用java需要几十行代码才能完成的事情,python往往只需要十几行,例如打开并且存储一个网页

java代码:

import java.io.BufferedReader;

import java.io.FileOutputStream;

import java.io.FileWriter;

import java.io.IOException;

import java.io.InputStreamReader;

import java.net.MalformedURLException;

import java.net.URL;

import java.net.URLConnection;

public class HeaderTest {

public static void main(String[] args) {

new HeaderTest().downloadHtml(“ ”);

}

public void downloadHtml(String link){

BufferedReader reader = null;

FileWriter writer = null;

try {

URL url = new URL(link);

URLConnection con = url.openConnection();

reader = new BufferedReader(new InputStreamReader(con.getInputStream()));

writer = new FileWriter(“f://test1.txt”);

String buff = null;

StringBuilder sb = new StringBuilder();

while((buff = reader.readLine()) != null){

writer.write(buff);

}

} catch (MalformedURLException e) {

// TODO Auto-generated catch block

e.printStackTrace();

} catch (IOException e) {

// TODO Auto-generated catch block

e.printStackTrace();

}finally{

try {

reader.close();

writer.close();

} catch (IOException e) {

// TODO Auto-generated catch block

e.printStackTrace();

}

}

}

}

python代码:

import urllib.request

def downloadHtml(link):
    try:
        data = urllib.request.urlopen(link).read()
        text = data.decode('utf-8','ignore')
        file = open('f:\\test2.txt','w')
        file.write(text)
        file.close()
    except urllib.request.URLError as e:
        print(e.reason)
downloadHtml("http://www.bilibili.com")

然而这种爬取网站的方式是不安全的,1是网站会根据访问者的类型来屏蔽访问.2是在爬取的时候访问网站会非常频繁,网站会封掉我们的IP

我们需要欺骗网站,在java中实现这一点比较常用的是使用HttpClient的jar包来实现

java代码如下

import java.io.BufferedInputStream;

import java.io.BufferedReader;

import java.io.IOException;

import java.io.InputStreamReader;

import org.apache.http.HttpEntity;

import org.apache.http.HttpHost;

import org.apache.http.HttpRequest;

import org.apache.http.HttpResponse;

import org.apache.http.client.ClientProtocolException;

import org.apache.http.client.config.RequestConfig;

import org.apache.http.client.methods.CloseableHttpResponse;

import org.apache.http.client.methods.HttpGet;

import org.apache.http.impl.client.CloseableHttpClient;

import org.apache.http.impl.client.HttpClients;

import org.apache.http.impl.execchain.MainClientExec;

public class HttpclientTest {

public static void main(String[] args){

System.out.println(new HttpclientTest().gethtml(“ ”));

}

public String gethtml(String url){

String html = null;

//建立HttpClient类,这是HttpClient的jar包中的一个类

CloseableHttpClient httpclient = HttpClients.createDefault();

//读取html的流

BufferedReader reader = null;

//设置请求信息

HttpGet getmethod = new HttpGet(url);

//响应

HttpResponse response = null;

//设置代理IP

HttpHost proxy = new HttpHost(“124.88.67.81”,80);

//设置超时时间

RequestConfig config = RequestConfig.custom().setProxy(proxy).setConnectTimeout(5000).setConnectionRequestTimeout(5000).setSocketTimeout(5000).build();

//添加请求头

getmethod.addHeader(“User-Agent”,“Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/56.0.2924.87 Safari/537.36”);

getmethod.setConfig(config);

try {

//获得响应

response = httpclient.execute(getmethod);

//响应体

HttpEntity entity = response.getEntity();

//建立一个读取流

reader = new BufferedReader(new InputStreamReader(entity.getContent()));

//读取html

String buff = null;

StringBuilder sb = new StringBuilder();

while((buff = reader.readLine()) != null){

sb.append(buff);

}

html = sb.toString();

System.out.println();

return html;

} catch (ClientProtocolException e) {

// TODO Auto-generated catch block

e.printStackTrace();

} catch (IOException e) {

// TODO Auto-generated catch block

System.out.println(“读取异常”);

return null;

}finally{

try {

httpclient.close();

reader.close();

} catch (IOException e) {

// TODO Auto-generated catch block

System.out.println(“关闭资源失败”);

}

}

}

}

在这段代码中我们设置了代理ip,请求头中的user-agent被我们设置成谷歌浏览器的内核,这样网站会认为我们是浏览器

python代码:

import urllib.request

def downloadHtml(link):
    try:
        proxy = {"http":"123.179.128.170:8080"}
        proxy_support = urllib.request.ProxyHandler(proxy)
        headers = ( "User-Agent","Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/56.0.2924.87 Safari/537.36")
        opener = urllib.request.build_opener(proxy_support)
        opener.addheaders = [headers]

opener = urllib.request.build_opener(proxy_support)

data = opener.open(link).read()        text = data.decode('utf-8','ignore')        print(text)    except urllib.request.URLError as e:        print(e.reason)def dowmloadHtml2(link):    req = urllib.request.Request(link)    req.add_header("User-Agent","Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/56.0.2924.87 Safari/537.36")    data = urllib.request.urlopen(req,timeout=1).read()    text = data.decode("utf-8","ignore")    print(text)downloadHtml("http://blog.csdn.net/weiwei_pig/article/details/51178226")