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 HttpURLConnectionhttpClient 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
//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。
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