Android HttpClient類的使用

一、HttpClient類的介紹

HttpClient是Apache下的一個Java開源項目，其作用是提供了一個高效、靈活、可擴展的處理HTTP請求的Java工具包，是用於Android上進行網絡通信的標準工具。

使用HttpClient可以很方便地在Android應用程序中執行HTTP請求，例如GET、POST等請求，獲取服務器發送的響應和狀態信息。

二、HttpClient請求流程

HttpClient請求的流程主要分為以下幾個步驟：

1. 創建 HttpClient 實例

    HttpClient httpClient = new DefaultHttpClient();

2. 創建 HttpGet 或 HttpPost 請求對象

    HttpGet httpGet = new HttpGet(url);
    HttpPost httpPost = new HttpPost(url);

3. 設置請求參數

    List<NameValuePair> paramList = new ArrayList<>();
    paramList.add(new BasicNameValuePair("username", "test"));
    paramList.add(new BasicNameValuePair("password", "123456"));
    UrlEncodedFormEntity entity = new UrlEncodedFormEntity(paramList, "UTF-8");
    httpPost.setEntity(entity);

4. 客戶端執行請求操作，並接收服務端返回的響應結果

    HttpResponse httpResponse = httpClient.execute(httpGet);

三、HttpClient基本請求

1、GET請求

GET請求通過在URL後添加參數來傳遞參數信息。下面是一個使用HttpClient發送GET請求的例子。

public static String sendHttpGetRequest(String url) {
    String response = "";
    try {
        HttpClient httpClient = new DefaultHttpClient();
        HttpGet httpGet = new HttpGet(url);
        HttpResponse httpResponse = httpClient.execute(httpGet);
        if (httpResponse.getStatusLine().getStatusCode() == HttpStatus.SC_OK) {
            HttpEntity entity = httpResponse.getEntity();
            if (entity != null) {
                response = EntityUtils.toString(entity, "UTF-8");
            }
        }
    } catch (Exception e) {
        e.printStackTrace();
    }
    return response;
}

2、POST請求

POST請求通過在請求體中添加參數來傳遞參數信息。下面是一個使用HttpClient發送POST請求的例子。

public static String sendHttpPostRequest(String url, Map<String, String> params) {
    String response = "";
    try {
        HttpClient httpClient = new DefaultHttpClient();
        HttpPost httpPost = new HttpPost(url);
        List<NameValuePair> paramList = new ArrayList<>();
        for (Map.Entry<String, String> entry : params.entrySet()) {
            paramList.add(new BasicNameValuePair(entry.getKey(), entry.getValue()));
        }
        UrlEncodedFormEntity entity = new UrlEncodedFormEntity(paramList, "UTF-8");
        httpPost.setEntity(entity);
        HttpResponse httpResponse = httpClient.execute(httpPost);
        if (httpResponse.getStatusLine().getStatusCode() == HttpStatus.SC_OK) {
            HttpEntity httpEntity = httpResponse.getEntity();
            if (httpEntity != null) {
                response = EntityUtils.toString(httpEntity, "UTF-8");
            }
        }
    } catch (Exception e) {
        e.printStackTrace();
    }
    return response;
}

四、HttpClient高級請求

1、HttpClient連接池

默認情況下，每次HttpClient請求操作都會創建一個新的HttpClient實例，如果在同一個應用程序中進行多次請求，這樣就會導致資源的浪費。因此，在實際開發中可以考慮使用HttpClient連接池來維護一組可用的HttpClient實例，減少資源的浪費。

public class HttpClientPool {
    private static PoolingHttpClientConnectionManager connMgr;
    private static RequestConfig requestConfig;
    private static final int MAX_TIMEOUT = 5000;

    static {
        connMgr = new PoolingHttpClientConnectionManager();
        connMgr.setMaxTotal(200);
        connMgr.setDefaultMaxPerRoute(connMgr.getMaxTotal());
        requestConfig = RequestConfig.custom()
                .setSocketTimeout(MAX_TIMEOUT)
                .setConnectTimeout(MAX_TIMEOUT)
                .setConnectionRequestTimeout(MAX_TIMEOUT)
                .build();
    }

    public static CloseableHttpClient getHttpClient() {
        CloseableHttpClient httpClient = HttpClients.custom()
                .setConnectionManager(connMgr)
                .setDefaultRequestConfig(requestConfig)
                .build();
        return httpClient;
    }
}

2、HttpClient攔截器

HttpClient攔截器是一個在請求執行前後對請求進行處理的機制。

攔截器可以在請求執行前添加一些公共屬性，比如請求頭、cookies等。也可以在請求執行成功後對返回的響應結果進行加工處理。

public class HttpHeaderInterceptor implements HttpRequestInterceptor {

    private Map<String, String> header;

    public HttpHeaderInterceptor(Map<String, String> header) {
        this.header = header;
    }

    @Override
    public void process(HttpRequest request, HttpContext context) {
        for (Map.Entry<String, String> entry : header.entrySet()) {
            request.addHeader(entry.getKey(), entry.getValue());
        }
    }
}

3、HttpClient文件上傳

HttpClient可以通過MultipartEntity來進行文件上傳操作。

public static String uploadFile(String url, Map<String, String> params, File file) {
    String response = "";
    try {
        CloseableHttpClient httpClient = HttpClients.createDefault();
        HttpPost httpPost = new HttpPost(url);
        MultipartEntityBuilder builder = MultipartEntityBuilder.create();
        builder.setMode(HttpMultipartMode.BROWSER_COMPATIBLE);
        for (Map.Entry<String, String> entry : params.entrySet()) {
            builder.addPart(entry.getKey(), new StringBody(entry.getValue(), ContentType.TEXT_PLAIN));
        }
        builder.addPart("filename", new FileBody(file));
        httpPost.setEntity(builder.build());
        CloseableHttpResponse httpResponse = httpClient.execute(httpPost);
        if (httpResponse.getStatusLine().getStatusCode() == HttpStatus.SC_OK) {
            response = EntityUtils.toString(httpResponse.getEntity(), "UTF-8");
        }
    } catch (Exception e) {
        e.printStackTrace();
    }
    return response;
}