Java如何处理HTTP重定向问题

在Java中，处理HTTP重定向问题通常是通过使用HTTP客户端库来实现的。这里以Apache HttpClient和Java内置的HttpURLConnection为例，介绍如何处理HTTP重定向。

1. 使用Apache HttpClient处理HTTP重定向：

Apache HttpClient提供了一个简单的API来处理HTTP重定向。默认情况下，HttpClient会自动处理重定向，你不需要做额外的设置。下面是一个简单的示例：

import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.HttpClients;

public class HttpClientExample {
    public static void main(String[] args) {
        HttpClient httpClient = HttpClients.createDefault();
        HttpGet httpGet = new HttpGet("http://example.com");

        try {
            HttpResponse httpResponse = httpClient.execute(httpGet);
            System.out.println("Status Code: " + httpResponse.getStatusLine().getStatusCode());
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

如果你想要自定义重定向策略，可以使用HttpClientBuilder来创建一个自定义的HttpClient实例：

import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
import org.apache.http.client.config.RequestConfig;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.impl.client.LaxRedirectStrategy;

public class HttpClientExample {
    public static void main(String[] args) {
        RequestConfig requestConfig = RequestConfig.custom()
                .setCircularRedirectsAllowed(false) // 禁止循环重定向
                .build();

        HttpClient httpClient = HttpClients.custom()
                .setRedirectStrategy(new LaxRedirectStrategy()) // 使用自定义的重定向策略
                .setDefaultRequestConfig(requestConfig)
                .build();

        HttpGet httpGet = new HttpGet("http://example.com");

        try {
            HttpResponse httpResponse = httpClient.execute(httpGet);
            System.out.println("Status Code: " + httpResponse.getStatusLine().getStatusCode());
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

2. 使用Java内置的HttpURLConnection处理HTTP重定向：

Java内置的HttpURLConnection默认会自动处理重定向。下面是一个简单的示例：

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

public class HttpURLConnectionExample {
    public static void main(String[] args) {
        try {
            URL url = new URL("http://example.com");
            HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();
            httpURLConnection.setInstanceFollowRedirects(true); // 启用自动重定向

            int statusCode = httpURLConnection.getResponseCode();
            System.out.println("Status Code: " + statusCode);

            BufferedReader in = new BufferedReader(new InputStreamReader(httpURLConnection.getInputStream()));
            String inputLine;
            StringBuilder content = new StringBuilder();

            while ((inputLine = in.readLine()) != null) {
                content.append(inputLine);
            }

            in.close();
            httpURLConnection.disconnect();

            System.out.println("Content: " + content.toString());
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

如果你想要禁用自动重定向，可以将setInstanceFollowRedirects方法的参数设置为false，然后手动处理重定向：

httpURLConnection.setInstanceFollowRedirects(false); // 禁用自动重定向
String location = httpURLConnection.getHeaderField("Location"); // 获取重定向的URL

这样，你就可以根据需要处理HTTP重定向问题了。