javaでgzipの実装

java で gzip の実装

```java:server.java
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.util.zip.GZIPOutputStream;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.http.HttpHeaders;
import org.springframework.http.MediaType;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
@RequestMapping("/test")
public class TestController {
    
    private static final Logger LOGGER = LoggerFactory.getLogger(TestController.class);

    @GetMapping
    public void test(HttpServletRequest request, HttpServletResponse reponse) throws IOException {
        
        // 响应体
        String content = "昔日龌龊不足夸，今朝放荡思无涯。春风得意马蹄疾，一日看尽长安花。";
        
        String acceptEncooding = request.getHeader(HttpHeaders.ACCEPT_ENCODING);
        
        /**
         * 获取客户端支持的编码格式，程序可以根据这个header判断是否要对响应体进行编码
         */
        LOGGER.info(acceptEncooding);
        
        
        // 响应体使用 gzip 编码
        reponse.setHeader(HttpHeaders.CONTENT_ENCODING, "gzip");
        // 响应体类型是字符串
        reponse.setContentType(MediaType.TEXT_PLAIN_VALUE);
        // 编码是utf-8
        reponse.setCharacterEncoding(StandardCharsets.UTF_8.displayName());
        // Gzip压缩后响应
        reponse.getOutputStream().write(gZip(content.getBytes(StandardCharsets.UTF_8)));
        
    }

    /**
     * Gzip压缩数据
     * @param data
     * @return
     * @throws IOException
     */
    public static byte[] gZip(byte[] data) throws IOException {
        ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
        try (GZIPOutputStream gzipOutputStream = new GZIPOutputStream(byteArrayOutputStream)) {
            gzipOutputStream.write(data);
            gzipOutputStream.finish();
            return byteArrayOutputStream.toByteArray();
        }
    }
}
```

```java:client.java
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.nio.charset.StandardCharsets;
import java.util.zip.GZIPInputStream;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.http.HttpEntity;
import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpMethod;
import org.springframework.http.MediaType;
import org.springframework.http.ResponseEntity;
import org.springframework.web.client.RestTemplate;

public class Main {

    public static final Logger LOGGER = LoggerFactory.getLogger(Main.class);

    public static void main(String[] args) throws Exception {
        
        RestTemplate restTemplate = new RestTemplate();
        
        
        HttpHeaders httpHeaders = new HttpHeaders();
        // Accept 表示客户端支持什么格式的响应体
        httpHeaders.set(HttpHeaders.ACCEPT, MediaType.TEXT_PLAIN_VALUE);
        // Accept-Encoding 头，表示客户端接收gzip格式的压缩
        httpHeaders.set(HttpHeaders.ACCEPT_ENCODING, "gzip");
        
        ResponseEntity<byte[]> responseEntity = restTemplate.exchange("http://localhost/test", HttpMethod.GET, new HttpEntity<>(httpHeaders), byte[].class);
        
        if (!responseEntity.getStatusCode().is2xxSuccessful()) {
            // TODO 非200响应
        }

        // 获取服务器响应体编码
        String contentEncoding = responseEntity.getHeaders().getFirst(HttpHeaders.CONTENT_ENCODING);
        
        if ("gzip".equals(contentEncoding)) { // gzip编码
            // gzip解压服务器的响应体
            byte[] data = unGZip(new ByteArrayInputStream(responseEntity.getBody()));
            
            LOGGER.info(new String(data, StandardCharsets.UTF_8));
        } else {
            // TODO 其他的编码
        }
    }

    /**
     * Gzip解压缩
     * @param inputStream
     * @return
     * @throws IOException
     */
    public static byte[] unGZip(InputStream inputStream) throws IOException {
        ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
        try (GZIPInputStream gzipInputStream = new GZIPInputStream(inputStream)) {
            byte[] buf = new byte[4096];
            int len = -1;
            while ((len = gzipInputStream.read(buf, 0, buf.length)) != -1) {
                byteArrayOutputStream.write(buf, 0, len);
            }
            return byteArrayOutputStream.toByteArray();
        } finally {
            byteArrayOutputStream.close();
        }
    }
}
```
以上！