Post请求的3种编码格式：application/x-www-form-urlencoded和multipart/form-data和application/json

本文主要是介绍Post请求的3种编码格式：application/x-www-form-urlencoded和multipart/form-data和application/json，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

一、前端表单提交时

application/x-www-form-urlencoded

表单代码：

<form action="http://localhost:8888/task/" method="POST">
First name: <input type="text" name="firstName" value="Mickey&"><br>
Last name: <input type="text" name="lastName" value="Mouse "><br>
<input type="submit" value="提交">
</form>

通过测试发现可以正常访问接口，在Chrome的开发者工具中可以看出，表单上传编码格式为application/x-www-form-urlencoded(Request Headers中)，参数的格式为key=value&key=value。

我们可以看出，服务器知道参数用符号&间隔，如果参数值中需要&，则必须对其进行编码。编码格式就是application/x-www-form-urlencoded（将键值对的参数用&连接起来，如果有空格，将空格转换为+加号；有特殊符号，将特殊符号转换为ASCII HEX值）。

application/x-www-form-urlencoded是浏览器默认的编码格式。对于Get请求，是将参数转换?key=value&key=value格式，连接到url后

ps：可以在这个网址测试表单：http://www.runoob.com/try/try.php?filename=tryhtml_form_submit

multipart/form-data

那么当服务器使用multipart/form-data接收POST请求时，服务器怎么知道每个参数的开始位置和结束位置呢？

<form action="http://localhost:8888/task/" method="POST" enctype="multipart/form-data">
First name: <input type="text" name="firstName" value="Mickey&"><br>
Last name: <input type="text" name="lastName" value="Mouse "><br>
<input type="submit" value="提交">
</form>

我们在开发者工具中可以看出multipart/form-data不会对参数编码，使用的boundary(分割线)，相当于&，boundary的值是----Web**AJv3。

文件上传

上传文件也要指定编码格式为multipart/form-data。

<form action="http://localhost:8888/testFile" enctype="multipart/form-data" method="POST">
<input type="file" name="file">
<input type="submit" value="提交">
</form>

如果是SpringMVC项目，要服务器能接受multipart/form-data类型参数，还要在spring上下文配置以下内容，SpringBoot项目则不需要。

<bean id="multipartResolver" class="org.springframework.web.multipart.commons.CommonsMultipartResolver"><property name="defaultEncoding" value="utf-8"></property>
</bean>

我们可以通过FormData对象模拟表单提交，用原始的XMLHttpRequest来发送数据，让我们可以在Chrome开发工具中查看到具体格式：

<form id="form">First name: <input type="text" name="firstName" value="Mickey"><br>Last name: <input type="text" name="lastName" value="Mouse"><br><input type="file" name="file"><br>
</form><button onclick="submitForm()">提交</button><script>function submitForm() {var formElement = document.getElementById("form");var xhr = new XMLHttpRequest();xhr.open("POST", "/task/testFile");xhr.send(new FormData(formElement));}
</script>

格式如下：

二、调用接口代码时

1、在代码中使用application/x-www-form-urlencoded编码格式设置Request属性调用接口，可以如下实现：

private static String doPost(String strUrl, String content) {String result = "";try {URL url = new URL(strUrl);//通过调用url.openConnection()来获得一个新的URLConnection对象，并且将其结果强制转换为HttpURLConnection.HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();urlConnection.setRequestMethod("POST");//设置连接的超时值为30000毫秒，超时将抛出SocketTimeoutException异常urlConnection.setConnectTimeout(30000);//设置读取的超时值为30000毫秒，超时将抛出SocketTimeoutException异常urlConnection.setReadTimeout(30000);//将url连接用于输出，这样才能使用getOutputStream()。getOutputStream()返回的输出流用于传输数据urlConnection.setDoOutput(true);//设置通用请求属性为默认浏览器编码类型urlConnection.setRequestProperty("content-type", "application/x-www-form-urlencoded");//getOutputStream()返回的输出流，用于写入参数数据。OutputStream outputStream = urlConnection.getOutputStream();outputStream.write(content.getBytes());outputStream.flush();outputStream.close();//此时将调用接口方法。getInputStream()返回的输入流可以读取返回的数据。InputStream inputStream = urlConnection.getInputStream();byte[] data = new byte[1024];StringBuilder sb = new StringBuilder();//inputStream每次就会将读取1024个byte到data中，当inputSteam中没有数据时，inputStream.read(data)值为-1while (inputStream.read(data) != -1) {String s = new String(data, Charset.forName("utf-8"));sb.append(s);}result = sb.toString();inputStream.close();} catch (IOException e) {e.printStackTrace();}return result;}public static void main(String[] args) {String str = doPost("http://localhost:8888/task/", "firstName=Mickey%26&lastName=Mouse ");System.out.println(str);}

2、在代码中使用multipart/form-data编码格式设置Request属性调用接口时，其中boundary的值可以在设置Content-Type时指定，让服务器知道如何拆分它接受的参数。通过以下代码的调用接口：

private static String doPost(String strUrl, Map<String, String> params, String boundary) {String result = "";try {URL url = new URL(strUrl);HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();urlConnection.setRequestMethod("POST");urlConnection.setConnectTimeout(30000);urlConnection.setReadTimeout(30000);urlConnection.setDoOutput(true);//设置通用请求属性为multipart/form-dataurlConnection.setRequestProperty("content-type", "multipart/form-data;boundary=" + boundary);DataOutputStream dataOutputStream = new DataOutputStream(urlConnection.getOutputStream());for (String key : params.keySet()) {String value = params.get(key);//注意！此处是\r(回车：将当前位置移到本行开头)、\n(换行：将当前位置移到下行开头)要一起使用dataOutputStream.writeBytes("--" + boundary + "\r\n");dataOutputStream.writeBytes("Content-Disposition: form-data; name=\"" + encode(key) + "\"\r\n");dataOutputStream.writeBytes("\r\n");dataOutputStream.writeBytes(encode(value) + "\r\n");}//最后一个分隔符的结尾后面要跟"--"dataOutputStream.writeBytes("--" + boundary + "--");dataOutputStream.flush();dataOutputStream.close();InputStream inputStream = urlConnection.getInputStream();byte[] data = new byte[1024];StringBuilder sb = new StringBuilder();while (inputStream.read(data) != -1) {String s = new String(data, Charset.forName("utf-8"));sb.append(s);}result = sb.toString();inputStream.close();} catch (Exception e) {e.printStackTrace();}return result;
}private static String encode(String value) throws UnsupportedEncodingException {return URLEncoder.encode(value, "UTF-8");
}public static void main(String[] args) {Map<String, String> params = new HashMap<>();params.put("firstName", "Mickey");params.put("lastName", "Mouse");//自定义boundary，有两个要求：使用不会出现在发送到服务器的HTTP数据中的值；并在请求消息中的分割位置都使用相同的值String boundary = "abcdefg";String str = doPost("http://localhost:8888/testFile", params, boundary);System.out.println(str);
}

通过debug，可以看出dataOutputStream的值如下：

三、使用Postman测试接口时

1、POST请求 -> Body -> x-www-form-urlencoded

当切换为x-www-form-urlencoded时，Headers会自动添加Content-Type:application/x-www-form-urlencoded

当请求Send后，此时点Code，可以查看到和Chrome开发工具中(Request Headers处的Content-Type和Form Data)一样的数据

2、POST请求 -> Body -> form-data

相当于html表单请求，value可为Text或文件。

可以不用手动指定编码格式，也可以指定编码为multipart/form-data

划线处的分割线应该是被省略了。

可以更改左上角的类型，来查看相应的Headers代码，常见的是下面三种：

Java OK HTTP：

JavaScript Jquery AJAX：

JavaScript XHR：

接口代码

@RequestMapping("/task")
public class TaskController {@RequestMapping("/")public String index(String firstName, String lastName) {//也可以从request中接收//String firstName= request.getParameter("firstName")==null?"":request.getParameter("firstName").toString();return firstName + lastName;}@RequestMapping("/testFile")public String testFile(String firstName, String lastName, MultipartFile file) {String result = firstName + lastName;if (file != null) {result += (file.getOriginalFilename() != null) ? file.getOriginalFilename() : "";}return result;}
}

POST请求的两种编码格式：application/x-www-urlencoded是浏览器默认的编码格式，用于键值对参数，参数之间用&间隔；multipart/form-data常用于文件等二进制，也可用于键值对参数，最后连接成一串字符传输(参考Java OK HTTP)。

除了这两个编码格式，还有application/json也经常使用。

application/json调用方式如下：

a) 使用httpClient

import org.apache.http.HttpResponse;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.entity.StringEntity;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.util.EntityUtils;import com.alibaba.fastjson.JSONObject;public class Sender {public static void main(String[] args) {String jsonData = "";try{CloseableHttpClient httpClient = HttpClients.createDefault();HttpPost post = new HttpPost("http://127.0.0.1:8091/json/data");post.addHeader("Content-Type", "application/json; charset=utf-8");// 设置请求body信息JSONObject body = new JSONObject();body.put("name", "wangru");body.put("address", "jinan");post.setEntity(new StringEntity(body.toString()));HttpResponse response = httpClient.execute(post);jsonData = EntityUtils.toString(response.getEntity());jsonData = UnicodeUtil.decodeUnicode(jsonData);System.out.println("接收反馈："+jsonData);}catch(Exception e){System.out.println(e.getMessage());}}}

b) 或者直接把数据写进流

public static String sendMessage4Json(){String jsonData = "";OutputStreamWriter out = null ;BufferedReader in = null;StringBuilder result = new StringBuilder();String url = "http://127.0.0.1:8091/json/data";logger.info("请求url："+url);try {URL realUrl = new URL(url);// 打开和URL之间的连接URLConnection conn = realUrl.openConnection();//设置通用的请求头属性conn.setRequestProperty("accept", "*/*");conn.setRequestProperty("connection", "Keep-Alive");conn.setRequestProperty("user-agent", "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1;SV1)");conn.setRequestProperty("Accept-Charset", "UTF-8");conn.setRequestProperty("Content-Type", "application/json;charset=UTF-8");// 发送POST请求必须设置如下两行   否则会抛异常（java.net.ProtocolException: cannot write to a URLConnection if doOutput=false - call setDoOutput(true)）conn.setDoOutput(true);conn.setDoInput(true);//获取URLConnection对象对应的输出流并开始发送参数out = new OutputStreamWriter(conn.getOutputStream(), "UTF-8");//添加参数String json = "{\"name\":\"wangru\",\"address\":\"jinan\"}";out.write(new String(json.getBytes("UTF-8")));out.flush();in = new BufferedReader(new InputStreamReader(conn.getInputStream(),"UTF-8"));String line;while ((line = in.readLine()) != null) {result.append(line);}} catch (Exception e) {e.printStackTrace();logger.info(e.getMessage());}finally {// 使用finally块来关闭输出流、输入流try {if (out != null) {out.close();}if (in != null) {in.close();}} catch (IOException ex) {ex.printStackTrace();logger.info(ex.getMessage());}}logger.info("接收反馈："+result.toString());jsonData = result.toString();return jsonData;}public static void main(String[] args) {sendMessage4Json();}

application/json接收方式如下：

@ResponseBody@RequestMapping(value = "/json/data3", method = RequestMethod.POST)public String getByJSON3 (HttpServletRequest request) {JSONObject result = new JSONObject();StringBuilder sb = new StringBuilder();InputStream is = null;try{is = request.getInputStream();byte[] b = new byte[4096];for (int n; (n = is.read(b)) != -1;){sb.append(new String(b, 0, n));}}catch (IOException e){e.printStackTrace();}finally{if (null != is){try{is.close();}catch (IOException e){e.printStackTrace();}}}result.put("json", sb);return result.toJSONString();}

或者用SpringBoot接收

    @ResponseBody@RequestMapping(value = "/json/data4", method = RequestMethod.POST, produces = "application/json;charset=UTF-8")public String getByJSON4(@RequestBody JSONObject jsonParam) {JSONObject result = new JSONObject();result.put("msg", "ok");result.put("data", jsonParam);return result.toJSONString();}