#IT明星不是夢#【從0開始Web開發實戰】SpringBoot集成HttpClient，開發進階

目錄：

1. SpringBoot集成HttpClient

2. 封裝服務HttpService.java，處理請求參數

3. 封裝ResponseHandler<T>，處理返回結果

4. 單元測試

5. 功能調用

6. 常見問題和解決方法

HttpClient是Apache Jakarta Common下的子項目，是一個高效的、功能豐富的HTTP客戶端編程工具包，以編程的方式通過API傳輸和接收HTTP消息。主要功能：

l 支持HTTP方法：GET, POST, PUT, DELETE, HEAD, OPTIONS等

l 支持HTTPS協議

l 支持多線程應用和連接管理，可設置最大連接數

l 支持KeepAlive持久連接

l 支持自定義Cookie策略

l 支持代理服務器：ngnix等

l 支持自動跳轉

l ......

本文分享SpringBoot集成和配置HttpClient的方法，並封裝HttpService調用請求和ResponseHandler處理返回結果，添加REST接口，演示項目中實際應用。

	代碼文件	功能要點
SpringBoot集成HttpClient	pom.xml	引入HttpClient依賴：org.apache.httpcomponents包裏的httpclient, httpcore, httpmime
	application.yml	配置HTTP連接屬性
	HttpConfig.java	配置Bean: HttpClient，以及RequestConfig和HttpClientConnectionManager
封裝服務HttpService	HttpService.java	處理HTTP請求參數，調用HttpClient發送請求
處理返回結果ResponseHandler<T>	RespStr.java RespJsonObj.java RespJsonArr.java RespFile.java	對HttpResponse進行處理，讀取HttpEntity並對返回內容進行轉換
單元測試	HttpServiceTest.java	測試HttpService發送請求和處理返回結果
功能調用	CheckController.java	增加REST接口/chk/http，發送HTTP請求並返回結果。

代碼下載：https://github.com/jextop/StarterApi/

一，SpringBoot集成HttpClient

1. 在pom.xml中添加httpclient, httpcore, httpmime依賴。

<dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpclient</artifactId>
    <version>4.5.2</version>
</dependency>
<dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpcore</artifactId>
    <version>4.4.4</version>
</dependency>
<dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpmime</artifactId>
    <version>4.5</version>
</dependency>

2. 在application.yml中配置HTTP連接屬性，指定最大連接數、超時時間等：

http:
  maxTotal: 100
  maxPerRoute: 20
  socketTimeout: 5000
  connectTimeout: 5000
  requestTimeout: 5000

3. 在HttpConfig.java中配置Bean，讀取HTTP連接屬性配置，聲明RequestConfig和HttpClientConnectionManager，並且創建HttpClient實例：

@Configuration
@ConfigurationProperties("http")
public class HttpConfig {
    private Integer maxTotal;
    private Integer maxPerRoute;
    private Integer socketTimeout;
    private Integer connectTimeout;
    private Integer requestTimeout;

    @Bean
    public HttpClientConnectionManager httpClientConnectionManager() {
        PoolingHttpClientConnectionManager connMgr = new PoolingHttpClientConnectionManager();
        connMgr.setMaxTotal(maxTotal);
        connMgr.setDefaultMaxPerRoute(maxPerRoute);
        return connMgr;
    }

    @Bean
    public RequestConfig requestConfig() {
        return RequestConfig.custom()
                .setSocketTimeout(socketTimeout)
                .setConnectTimeout(connectTimeout)
                .setConnectionRequestTimeout(requestTimeout)
                .build();
    }

    @Bean
    public HttpClient httpClient(HttpClientConnectionManager manager, RequestConfig config) {
        return HttpClientBuilder.create()
                .setConnectionManager(manager)
                .setDefaultRequestConfig(config)
                .build();
    }

}

二，封裝服務HttpService.java，處理請求參數，調用HttpClient發送請求。

@Service
public class HttpService {
    @Autowired
    private HttpClient httpClient;

    public <T> T sendRequest(HttpRequestBase httpRequest, ResponseHandler<T> handler) {
        try {
            return httpClient.execute(httpRequest, handler);
        } catch (ClientProtocolException e) {
            LogUtil.error("Error when sendRequest", e.getMessage());
        } catch (IOException e) {
            LogUtil.error("Error when sendRequest", e.getMessage());
        }
        return null;
    }

    public <T> T sendHttpGet(String url, ResponseHandler<T> handler) {
        return sendRequest(new HttpGet(url), handler);
    }

    public String sendHttpGet(String url) {
        return sendHttpGet(url, new RespStr());
    }

    public <T> T sendHttpGet(String url, Map<String, String> headers, ResponseHandler<T> handler) {
        HttpGet httpGet = new HttpGet(url);
        fillHeaders(httpGet, headers);
        return sendRequest(httpGet, handler);
    }

    private static void fillHeaders(HttpRequestBase request, Map<String, String> headers) {
        for (Map.Entry<String, String> header : headers.entrySet()) {
            request.addHeader(header.getKey(), header.getValue());
        }
    }
}

HttpService中使用RespStr處理HttpResponse，返回字符串。

三，封裝ResponseHandler<T>，處理返回結果

ResponseHandler<T>是httpclient包內提供的接口，實現函數handleResponse()處理HTTP返回結果，封裝處理邏輯。

package org.apache.http.client;

import java.io.IOException;
import org.apache.http.HttpResponse;

public interface ResponseHandler<T> {
    T handleResponse(HttpResponse var1) throws ClientProtocolException, IOException;
}

封裝的4個HTTP返回結果處理類，簡化邏輯，提高開發效率。

代碼文件	HTTP返回結果類型
RespStr.java	返回字符串
RespJsonObj.java	返回JSONObject
RespJsonArr.java	返回JSONArray
RespFile.java	返回二進制文件

1. RespStr.java：讀取HttpResponse返回的內容，格式化爲String字符串

- 調用httpResponse.getEntiry()獲取返回結果

- 調用ContentType.get()獲取內容類型

- 調用ContentType.getCharset()獲取編碼格式

- 調用EntityUtils.toString()將返回結果格式化爲字符串

public class RespStr implements ResponseHandler<String> {
    @Override
    public String handleResponse(HttpResponse httpResponse) throws ClientProtocolException, IOException {
        HttpEntity entity = httpResponse.getEntity();
        ContentType contentType = ContentType.getOrDefault(entity);
        Charset charset = contentType.getCharset();
        return EntityUtils.toString(entity, charset);
    }
}

2. RespJsonObj.java：在返回結果爲JSON對象時，轉換成JSONObject返回

public class RespJsonObj implements ResponseHandler<JSONObject> {
    @Override
    public JSONObject handleResponse(HttpResponse resp) throws ClientProtocolException, IOException {
        HttpEntity entity = resp.getEntity();
        ContentType contentType = ContentType.getOrDefault(entity);
        Charset charset = contentType.getCharset();
        String jsonStr = EntityUtils.toString(entity, charset);

        // parse JSON object
        return JsonUtil.parseObj(jsonStr);
    }
}

3. RespJsonArr.java：將HTTP請求返回結果轉換成JSONArray返回

public class RespJsonArr implements ResponseHandler<JSONArray> {
    @Override
    public JSONArray handleResponse(HttpResponse resp) throws ClientProtocolException, IOException {
        HttpEntity entity = resp.getEntity();
        ContentType contentType = ContentType.getOrDefault(entity);
        Charset charset = contentType.getCharset();
        String jsonStr = EntityUtils.toString(entity, charset);

        // parse JSON array
        return JsonUtil.parseArr(jsonStr);
    }
}

4. RespFile.java：在HTTP返回二進制文件時，從Entity中讀取二進制內容，並可從Header中獲取文件名稱。

public class RespFile implements ResponseHandler<byte[]> {
    private static final String fileNameFlag = "attachment;fileName=";

    private byte[] bytes;
    private String fileName;

    public byte[] getBytes() {
        return bytes;
    }

    public String getFileName() {
        return fileName;
    }

    @Override
    public byte[] handleResponse(HttpResponse response) throws ClientProtocolException, IOException {
        // Header: Content-Disposition: attachment;fileName=abc.txt
        Header header = response.getFirstHeader("Content-Disposition");
        String headerValue = header.getValue();
        if (headerValue.startsWith(fileNameFlag)) {
            fileName = headerValue.substring(fileNameFlag.length(), headerValue.length());
        }

        HttpEntity entity = response.getEntity();
        bytes = EntityUtils.toByteArray(entity);
        return bytes;
    }
}

四，單元測試，調用HttpService發送請求和處理返回結果

 

五，功能調用

1. 增加RestController：CheckController.java

2. 增加REST接口/chk/http，發送HTTP請求並返回結果。

@GetMapping(value = "/chk/http", produces = "application/json")
public Object http() {
    String strCourse = httpService.sendHttpGet("https://edu.51cto.com/lecturer/13841865.html");
    String[] courses = StrUtil.parse(strCourse, "[1-9]\\d*人學習");

    return new HashMap<String, Object>() {{
        put("chk", "http");
        put("course", courses);
    }};
}

3. REST接口調用HttpSevice示例

 

六，常見問題和解決方法

l HTTP返回結果亂碼，設置UTF-8仍然不能解決？

原因：處理HTTP請求返回結果時，出現亂碼是因爲設置Charset編碼格式不正確，通常設置UTF-8可以解決大部分情況，但並不是所有HTTP服務器都一定使用UTF-8格式。

解決：正確的方法是獲取內容編碼時的格式：

- 調用httpResponse.getEntiry()獲取返回結果

- 調用ContentType.get()獲取內容類型

- 調用ContentType.getCharset()獲取編碼格式

- 調用EntityUtils.toString()將返回結果格式化爲字符串

public class RespStr implements ResponseHandler<String> {
    @Override
    public String handleResponse(HttpResponse httpResponse) throws ClientProtocolException, IOException {
        HttpEntity entity = httpResponse.getEntity();
        ContentType contentType = ContentType.getOrDefault(entity);
        Charset charset = contentType.getCharset();
        return EntityUtils.toString(entity, charset);
    }
}

ResponseHandler<T>是httpclient包內提供的接口，實現函數handleResponse()處理HTTP返回結果。