HttpURLConnection可以post上传任意格式的raw文本，包括text、json、xml、html等数据。其实就是post的时候，不指定key键，直接将需要传参的数据输出，即是 getOutputStream().write(data)。

实现代码

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLEncoder;
import java.util.Iterator;
import java.util.Map;

public class HttpPostRaw {
    // 设置连接主机服务器的超时时间：15000毫秒
    private final int CONNECT_TIMEOUT = 15000;
    // 设置读取远程返回的数据时间：60000毫秒
    private final int READ_TIMEOUT = 60000;

    private HttpURLConnection httpConn;
    private String postData;
    private String charset;

    /**
     * 构造方法
     *
     * @param requestURL  请求地址
     * @param charset     请求的编码
     * @param headers     请求头
     * @param postData    请求字段
     * @throws IOException
     */
    public HttpPostRaw(String requestURL, String charset, Map<String, String> headers, String postData) throws IOException {
        this.charset = charset;
        this.postData = postData;
        URL url = new URL(requestURL);
        httpConn = (HttpURLConnection) url.openConnection();
        httpConn.setConnectTimeout(CONNECT_TIMEOUT);
        httpConn.setReadTimeout(READ_TIMEOUT);
        httpConn.setUseCaches(false);
        httpConn.setDoOutput(true);    // 表明是post请求
        httpConn.setDoInput(true);
        httpConn.setRequestProperty("Content-Type", "text/plain");
        if (headers != null && headers.size() > 0) {
            Iterator<String> it = headers.keySet().iterator();
            while (it.hasNext()) {
                String key = it.next();
                String value = headers.get(key);
                httpConn.setRequestProperty(key, value);
            }
        }
    }

    public HttpPostRaw(String requestURL, String charset, Map<String, String> headers) throws IOException {
        this(requestURL, charset, headers, null);
    }

    public HttpPostRaw(String requestURL, String charset) throws IOException {
        this(requestURL, charset, null, null);
    }

    /**
     * 添加请求头
     *
     * @param key
     * @param value
     */
    public void addHeader(String key, String value) {
        httpConn.setRequestProperty(key, value);
    }

    /**
     * 设置请求数据
     * @param postData
     */
    public void setPostData(String postData) {
        this.postData = postData;
    }

    /**
     * 将请求字段转化成byte数组
     *
     * @return
     */
    private byte[] getParamsByte() {
        byte[] result = null;
        try {
            result = this.postData.toString().getBytes("UTF-8");
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        }
        return result;
    }

    /**
     * 对键和值进行url编码
     *
     * @param data
     * @return
     */
    private String encodeParam(String data) {
        String result = "";
        try {
            result = URLEncoder.encode(data, "UTF-8");
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        }
        return result;
    }

    /**
     * 完成请求，并接受服务器的回应
     *
     * @return 如果请求成功，状态码是200，返回服务器返回的字符串，否则抛出异常
     * @throws IOException
     */
    public String finish() throws IOException {
        String response = "";
        byte[] postDataBytes = this.getParamsByte();
        httpConn.getOutputStream().write(postDataBytes);
        // 检查服务器返回状态
        int status = httpConn.getResponseCode();
        if (status == HttpURLConnection.HTTP_OK) {
            ByteArrayOutputStream result = new ByteArrayOutputStream();
            byte[] buffer = new byte[1024];
            int length;
            while ((length = httpConn.getInputStream().read(buffer)) != -1) {
                result.write(buffer, 0, length);
            }
            response = result.toString(this.charset);
            httpConn.disconnect();
        } else {
            throw new IOException("Server returned non-OK status: " + status);
        }
        return response;
    }
}

调用示例

try {
    HttpPostRaw post = new HttpPostRaw("http://localhost/json", "utf-8");
    String json = "{\"id\":\"288285\",\"value\":\"测试\"}";
    post.setPostData(json);
    post.addHeader("Content-Type", "application/json");
    String out = post.finish();
    System.out.println(out);
} catch (Exception e) {
    e.printStackTrace();
}