安卓App使用HttpURLConnection发送请求与上传文件

安卓原生App开发时常用的http开发工具

• 系统内置http请求工具为 HttpURLConnection
• httpClient 是 apache 的开源工具
• okHttp 使用更简单，语法相对HttpURLConnection也简洁了许多，需要在graddle添加依赖。

本文主要讲解如何使用HttpURConnection向服务器发送Reqest, 保存Response内容，如何上传文件等内容。

1. 使用 HttpURLConnection 发送http GET请求

step-1: 创建1个URL 对象

URL url = new URL("http://www.yahoo.com");

step-2: 创建1个 HttpURLConnection对象，并绑定URL对象 object,

HttpURLConnection httpConn = (HttpURLConnection)url.openConnection();

step-3: 设置请求方法，以及其它必要选项

httpConn.setConnectTimeout(10000);
httpConn.setRequestMethod("GET");

设置了请求方法后，就开始发送

step-4: 读取 Response
在httpConn对象上打开1个input stream, 用BufferReader的方式从httpConnect中读字节

InputStream inputStream = httpConn.getInputStream();
InputStreamReader inputStreamReader = new InputStreamReader(inputStream);
BufferedReader bufferedReader = new BufferedReader(inputStreamReader);
//保存response内容
StringBuffer readTextBuf = new StringBuffer();
String line = bufferedReader.readLine();
while(line != null) {
    readTextBuf.append(line);
    // Continue to read text line.
    line = bufferedReader.readLine();
}

step-5: 读完response以后，此连接就不需要了，别忘了关闭连接

httpConn.disconnect();

2. 发送 POST请求步骤

与GET请求步骤不同在于，POST 需要在消息体内携带请求参数，因此要在httpConn连接上打开ouput stream，才能发出
将第1节的step-3 改为如下：

httpConn.setRequestMethod("GET");
httpConn.setRequestProperty(“Key”,”Value”);
httpConn.setDoOutput(true);

Output the stream to the server
OutputStream outputPost = new BufferedOutputStream(httpConn.getOutputStream());
writeStream(outputPost);
outputPost.flush();
outputPost.close();

至此，POST消息发送完成。 读取Response响应体的方法与上节相同。

下面是1个完整的发送POST 示例

(1)准备1个HashMap(类似于python字典）保存请求参数

HashMap params;
//此处添加
params.put("name", "Jack");
params.put("company", "Baidu");

(2)将HashMap转为stringBuild类型

 StringBuilder sbParams = new StringBuilder();
    int i = 0;
    for (String key : params.keySet()) {
        try {
            if (i != 0){
                sbParams.append("&");
            }
            sbParams.append(key).append("=")
                    .append(URLEncoder.encode(params.get(key), "UTF-8"));

        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        }
        i++;
    }

(3) 创建 HttpURLConnection 对象，打开连接，发送POST请求参数

try{
    String url = "http://www.example.com/test.php";
    URL urlObj = new URL(url);
    HttpURLConnection conn = (HttpURLConnection) urlObj.openConnection();
    conn.setDoOutput(true);
    conn.setRequestMethod("POST");
    conn.setRequestProperty("Accept-Charset", "UTF-8");
    
    conn.setReadTimeout(10000);
    conn.setConnectTimeout(15000);
    
    conn.connect();
    
    String paramsString = sbParams.toString();  //sbParams是前面准备好的
    
    DataOutputStream wr = new DataOutputStream(conn.getOutputStream());
    wr.writeBytes(paramsString);
    wr.flush();
    wr.close();
} catch (IOException e) {
  e.printStackTrace();
}

(4)接收response, 保存body 内容

try {
  InputStream in = new BufferedInputStream(conn.getInputStream());
  BufferedReader reader = new BufferedReader(new InputStreamReader(in));
  StringBuilder result = new StringBuilder();
  String line;
  while ((line = reader.readLine()) != null) {
    result.append(line);
  }

  Log.d("test", "result from server: " + result.toString());

} catch (IOException e) {
  e.printStackTrace();
} finally {
    if (conn != null) {
        conn.disconnect();
    }
}

3. 发送Json POST request

与普通的POST请求不同，JSON POST请求参数为json格式, 因此需要修改请求头部参数Content-Type与Accept参数

修改step-3步骤:

httpConn.setRequestMethod("POST");

设置Content-Type头部参数为“application/json”

httpConn.setRequestProperty("Content-Type", "application/json");

设置“Accept”头部参数为“application/json”

httpConn.setRequestProperty("Accept", "application/json");

设置连接准备发送数据

httpConn.setDoOutput(true);

创建1个json body

String jsonInputString = "{"name": "Upendra", "job": "Programmer"}";

将json字符串写入output stream

try(OutputStream os = httpConn.getOutputStream()) {
   byte[] input = jsonInputString.getBytes("utf-8");
   os.write(input, 0, input.length); 
}

4. 用POST请求上传文件

上传文件时，POST请求头部参数Content-Type使用 multipart/form-data, 实现也比较容易

URL url = new URL(postTarget);
HttpURLConnection connection = (HttpURLConnection) url.openConnection();

String auth = "Bearer " + oauthToken;
connection.setRequestProperty("Authorization", basicAuth);

String boundary = UUID.randomUUID().toString();
connection.setRequestMethod("POST");
connection.setDoOutput(true);
connection.setRequestProperty("Content-Type", "multipart/form-data;boundary=" + boundary);

DataOutputStream request = new DataOutputStream(uc.getOutputStream());

request.writeBytes("--" + boundary + "\r\n");
request.writeBytes("Content-Disposition: form-data; name=\"description\"\r\n\r\n");
request.writeBytes(fileDescription + "\r\n");

request.writeBytes("--" + boundary + "\r\n");
request.writeBytes("Content-Disposition: form-data; name=\"file\"; filename=\"" + file.fileName + "\"\r\n\r\n");
request.write(FileUtils.readFileToByteArray(file));
request.writeBytes("\r\n");

request.writeBytes("--" + boundary + "--\r\n");
request.flush();
int respCode = connection.getResponseCode();

switch(respCode) {
    case 200:
        //all went ok - read response
        ...
        break;
    case 301:
    case 302:
    case 307:
        //handle redirect - for example, re-post to the new location
        ...
        break;
    ...
    default:
        //do something sensible
}

总结

使用 HttpURLConnection 发送请求流程还是比较清晰，GET, POST,主要的区别在Step-3 步骤，发送 JSON类型参数，上传 file 还需要修改头部参数。
在Android App开发时，可以在Activity用按钮事件来触发请求，也可以使用service 在后台发送请求。 本文就不列出那些示例代码了。