(調査中)Apache HttpClient 4.5 でGZIP 圧縮されたレスポンスを処理

自動解凍の場合

import org.apache.http.HttpEntity;
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.util.EntityUtils;

public class GzipClientAuto {
    public static void main(String[] args) throws Exception {
        try (CloseableHttpClient client = HttpClients.createDefault()) {
            HttpGet request = new HttpGet("http://localhost:8080/gzip");
            request.addHeader("Accept-Encoding", "gzip");

            try (CloseableHttpResponse response = client.execute(request)) {
                HttpEntity entity = response.getEntity();
                String body = EntityUtils.toString(entity, "UTF-8");
                System.out.println("Response: " + body);
            }
        }
    }
}

手動で GZIP 解凍する場合

import org.apache.http.HttpEntity;
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 java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.InputStream;
import java.util.zip.GZIPInputStream;

public class GzipClientManual {
    public static void main(String[] args) throws Exception {
        try (CloseableHttpClient client = HttpClients.createDefault()) {
            HttpGet request = new HttpGet("http://localhost:8080/gzip");
            request.addHeader("Accept-Encoding", "gzip");

            try (CloseableHttpResponse response = client.execute(request)) {
                HttpEntity entity = response.getEntity();
                String contentEncoding = response.getFirstHeader("Content-Encoding") != null
                        ? response.getFirstHeader("Content-Encoding").getValue()
                        : "";

                InputStream inputStream = entity.getContent();
                if ("gzip".equalsIgnoreCase(contentEncoding)) {
                    inputStream = new GZIPInputStream(inputStream);
                }

                BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream, "UTF-8"));
                String line;
                while ((line = reader.readLine()) != null) {
                    System.out.println("Response: " + line);
                }
            }
        }
    }
}

まとめ

解凍方法	特徴
自動（EntityUtils.toString()）	一般的で簡単。Content-Encoding を自動処理。
手動（GZIPInputStream）	カスタム処理や細かい制御が必要な場合に適用。