403禁止与Java，但不是网络浏览器？

Question

我正在编写一个小Java程序，以获取给定谷歌搜索词的结果量。出于某种原因，在Java中我得到了403，但我在web浏览器中得到了正确的结果。代码：

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.URL;


public class DataGetter {

    public static void main(String[] args) throws IOException {
        getResultAmount("test");
    }

    private static int getResultAmount(String query) throws IOException {
        BufferedReader r = new BufferedReader(new InputStreamReader(new URL("https://www.google.com/search?q=" + query).openConnection()
                .getInputStream()));
        String line;
        String src = "";
        while ((line = r.readLine()) != null) {
            src += line;
        }
        System.out.println(src);
        return 1;
    }

}

和错误：

Exception in thread "main" java.io.IOException: Server returned HTTP response code: 403 for URL: https://www.google.com/search?q=test
    at sun.net.www.protocol.http.HttpURLConnection.getInputStream(Unknown Source)
    at sun.net.www.protocol.https.HttpsURLConnectionImpl.getInputStream(Unknown Source)
    at DataGetter.getResultAmount(DataGetter.java:15)
    at DataGetter.main(DataGetter.java:10)

它为什么这样做？

Answer 1

您可能没有设置正确的标头。在浏览器中使用LiveHttpHeaders（或等效）查看浏览器发送的标头，然后在代码中模拟它们。

Answer 2

对我来说，它通过添加标题：“Accept”：“*/*”起作用

Answer 3

您只需设置用户代理标头即可使其工作：

URLConnection connection = new URL("https://www.google.com/search?q=" + query).openConnection();
connection.setRequestProperty("User-Agent", "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.11 (KHTML, like Gecko) Chrome/23.0.1271.95 Safari/537.11");
connection.connect();

BufferedReader r  = new BufferedReader(new InputStreamReader(connection.getInputStream(), Charset.forName("UTF-8")));

StringBuilder sb = new StringBuilder();
String line;
while ((line = r.readLine()) != null) {
    sb.append(line);
}
System.out.println(sb.toString());

从异常堆栈跟踪中可以看出，SSL是透明处理的。

然而，获得结果量并不是那么简单，在这之后，你必须通过获取cookie并解析重定向令牌链接来假装你是一个浏览器。

String cookie = connection.getHeaderField( "Set-Cookie").split(";")[0];
Pattern pattern = Pattern.compile("content=\\\"0;url=(.*?)\\\"");
Matcher m = pattern.matcher(response);
if( m.find() ) {
    String url = m.group(1);
    connection = new URL(url).openConnection();
    connection.setRequestProperty("User-Agent", "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.11 (KHTML, like Gecko) Chrome/23.0.1271.95 Safari/537.11");
    connection.setRequestProperty("Cookie", cookie );
    connection.connect();
    r  = new BufferedReader(new InputStreamReader(connection.getInputStream(), Charset.forName("UTF-8")));
    sb = new StringBuilder();
    while ((line = r.readLine()) != null) {
        sb.append(line);
    }
    response = sb.toString();
    pattern = Pattern.compile("<div id=\"resultStats\">About ([0-9,]+) results</div>");
    m = pattern.matcher(response);
    if( m.find() ) {
        long amount = Long.parseLong(m.group(1).replaceAll(",", ""));
        return amount;
    }

}

运行完整的代码后，我得到了29300000L。