如何使用 ApacheHttpClient 发布 JSON 请求？

Apache HttpClient doesn't know anything about JSON, so you'll need to construct your JSON separately. To do so, I recommend checking out the simple JSON-java library from json.org. (If "JSON-java" doesn't suit you, json.org has a big list of libraries available in different languages.)

Once you've generated your JSON, you can use something like the code below to POST it

StringRequestEntity requestEntity = new StringRequestEntity(
JSON_STRING,
"application/json",
"UTF-8");


PostMethod postMethod = new PostMethod("http://example.com/action");
postMethod.setRequestEntity(requestEntity);


int statusCode = httpClient.executeMethod(postMethod);

Edit

Note - The above answer, as asked for in the question, applies to Apache HttpClient 3.1. However, to help anyone looking for an implementation against the latest Apache client:

StringEntity requestEntity = new StringEntity(
JSON_STRING,
ContentType.APPLICATION_JSON);


HttpPost postMethod = new HttpPost("http://example.com/action");
postMethod.setEntity(requestEntity);


HttpResponse rawResponse = httpclient.execute(postMethod);

As mentioned in the excellent answer by janoside, you need to construct the JSON string and set it as a StringEntity.

To construct the JSON string, you can use any library or method you are comfortable with. Jackson library is one easy example:

import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.node.ObjectNode;
import org.apache.http.entity.ContentType;
import org.apache.http.entity.StringEntity;


ObjectMapper mapper = new ObjectMapper();
ObjectNode node = mapper.createObjectNode();
node.put("name", "value"); // repeat as needed
String JSON_STRING = node.toString();
postMethod.setEntity(new StringEntity(JSON_STRING, ContentType.APPLICATION_JSON));

For Apache HttpClient 4.5 or newer version:

    CloseableHttpClient httpclient = HttpClients.createDefault();
HttpPost httpPost = new HttpPost("http://targethost/login");
String JSON_STRING="";
HttpEntity stringEntity = new StringEntity(JSON_STRING,ContentType.APPLICATION_JSON);
httpPost.setEntity(stringEntity);
CloseableHttpResponse response2 = httpclient.execute(httpPost);

Note:

1 in order to make the code compile, both httpclient package and httpcore package should be imported.

2 try-catch block has been ommitted.

Reference: appache official guide

the Commons HttpClient project is now end of life, and is no longer being developed. It has been replaced by the Apache HttpComponents project in its HttpClient and HttpCore modules

I use JACKSON library to convert object to JSON and set the request body like below. Here is full example.

try (CloseableHttpClient httpclient = HttpClients.createDefault()) {


HttpPost httpPost = new HttpPost("https://jsonplaceholder.typicode.com/posts");


Post post = new Post("foo", "bar", 1);
ObjectWriter ow = new ObjectMapper().writer();
String strJson = ow.writeValueAsString(post);
System.out.println(strJson);


StringEntity strEntity = new StringEntity(strJson, ContentType.APPLICATION_JSON);
httpPost.setEntity(strEntity);
httpPost.setHeader("Content-type", "application/json");


try (CloseableHttpResponse response = httpclient.execute(httpPost)) {
System.out.println(response.getCode() + " " + response.getReasonPhrase());


HttpEntity entity = response.getEntity();
String result = EntityUtils.toString(entity);
System.out.println(result);


EntityUtils.consume(entity);
} catch (ParseException e) {
e.printStackTrace();
}


} catch (IOException e) {
System.out.println(e.getMessage());
}