使用JAVA发送post请求，一个试了两次，一次是400一次是415

Question

这个是415

httpURLConnection.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");

这个是400

httpURLConnection.setRequestProperty("Content-Type", "application/json; charset=utf-8");

package com.bulldozer.utils;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.UnsupportedEncodingException;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLEncoder;
import java.util.HashMap;
import java.util.Map;

public class HttpUtil {

    // 表示服务器端的url
    private static String PATH = "http://8.140.147.123:9090/v1/refuse-treatment-plant";
    private static URL url;

    public HttpUtil() {
        // TODO Auto-generated constructor stub
    }

    static {
        try {
            url = new URL(PATH);
        } catch (MalformedURLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    /*
     * params 填写的URL的参数 encode 字节编码
     */
    public static String sendPostMessage(Map<String, String> params,
                                         String encode) {

        StringBuffer stringBuffer = new StringBuffer();

        if (params != null && !params.isEmpty()) {
            for (Map.Entry<String, String> entry : params.entrySet()) {
                try {
                    stringBuffer
                            .append(entry.getKey())
                            .append("=")
                            .append(URLEncoder.encode(entry.getValue(), encode))
                            .append("&");

                } catch (UnsupportedEncodingException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
            // 删掉最后一个 & 字符
            stringBuffer.deleteCharAt(stringBuffer.length() - 1);
            System.out.println("-->>" + stringBuffer.toString());

            try {
                HttpURLConnection httpURLConnection = (HttpURLConnection) url
                        .openConnection();
                httpURLConnection.setConnectTimeout(3000);
                httpURLConnection.setDoInput(true);// 从服务器获取数据
                httpURLConnection.setDoOutput(true);// 向服务器写入数据

                // 获得上传信息的字节大小及长度
                byte[] mydata = stringBuffer.toString().getBytes();
                // 设置请求体的类型
//                httpURLConnection.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");
                httpURLConnection.setRequestProperty("Content-Type", "application/json; charset=utf-8");
                httpURLConnection.setRequestProperty("Content-Lenth",
                        String.valueOf(mydata.length));

                // 获得输出流，向服务器输出数据
                OutputStream outputStream = (OutputStream) httpURLConnection
                        .getOutputStream();
                outputStream.write(mydata);

                // 获得服务器响应的结果和状态码
                int responseCode = httpURLConnection.getResponseCode();
                System.out.println("responseCode == " + responseCode);
                if (responseCode == 200) {

                    // 获得输入流，从服务器端获得数据
                    InputStream inputStream = (InputStream) httpURLConnection
                            .getInputStream();
                    return (changeInputStream(inputStream, encode));

                }

            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }

        return "";
    }

    /*
     * // 把从输入流InputStream按指定编码格式encode变成字符串String
     */
    public static String changeInputStream(InputStream inputStream,
                                           String encode) {

        // ByteArrayOutputStream 一般叫做内存流
        ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
        byte[] data = new byte[1024];
        int len = 0;
        String result = "";
        if (inputStream != null) {

            try {
                while ((len = inputStream.read(data)) != -1) {
                    byteArrayOutputStream.write(data, 0, len);

                }
                result = new String(byteArrayOutputStream.toByteArray(), encode);

            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

        }

        return result;
    }

    /**
     * @param args
     */
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Map<String, String> params = new HashMap<String, String>();
        params.put("licenseNumber", "FTYYUTYA");
        params.put("plantName", "中国");
        String result = sendPostMessage(params, "utf-8");
        System.out.println("-result->>" + result);


    }
}

Answer 1

415(不支持的媒体类型)，post请求 需要设置请求头

json.xhr.setRequestHeader('Content-Type','application/json')

400指的是请求无效（请求有语法问题或者不能满足请求）
解决办法：对传递的数据进行json序列

已参与了 SegmentFault 思否「问答」打卡，欢迎正在阅读的你也加入。

Answer 2

这个415和400的话，你只是贴你的客户端代码是没用的，但是也可以从错误里面猜出个大概

415是说服务端不接受你的媒体格式，也就是application/x-www-form-urlencoded
这说明你不能用application/x-www-form-urlencoded了
用application/json; charset=utf-8返回400，说明服务端接受了你的请求，但是处理错误了，然后看你的代码，你发的还是form表单类的数据，你可以尝试把数据已json字符串发送，看看服务端是否正常处理

Answer 3

建议不要把实际环境的请求地址暴露出来，我点了一下竟然能返回数据。。。