安卓通过json格式将数据传到服务器（后端）。

1.后端返回值要是json格式，
2.安卓端要以json格式传到服务器

创建 andriod项目
在 build.gradle下面添加 两个jar包

implementation 'commons-httpclient:commons-httpclient:3.1'
    implementation 'com.alibaba:fastjson:1.2.44'

下面是一个写的完成安卓将数据传送到服务器的一个class

`package com.example.cashbookforapp.service;

import com.alibaba.fastjson.JSONObject;
import com.example.cashbookforapp.pojo.Orderitem;
import com.example.cashbookforapp.pojo.User;

import org.apache.commons.httpclient.HttpClient;
import org.apache.commons.httpclient.HttpException;
import org.apache.commons.httpclient.methods.PostMethod;
import org.apache.commons.httpclient.params.HttpMethodParams;

import java.io.IOException;
import java.util.Map;
import java.util.Set;

public class AddOrderItemService {
    //你要訪問的地址
    static String url="http://10.0.2.2:8080/项目名称/xxxx";
   这里的class是自己定义的一个实体对象
    public static String postHttp(Class class) {
        //方法一,将class转为json
    String body = JSONObject.toJSONString(class);
	//定义返回的结果 
    String mesg = null;
    //构建HttpClient实例
    HttpClient httpClient = new HttpClient();
    //设置请求超时时间
    httpClient.getHttpConnectionManager().getParams().setConnectionTimeout(60000);
    //设置响应超时时间
    httpClient.getHttpConnectionManager().getParams().setSoTimeout(60000);

    //构造PostMethod的实例
    PostMethod postMethod=new PostMethod(url);
    postMethod.getParams().setParameter(HttpMethodParams.HTTP_CONTENT_CHARSET,"utf-8");
    Map map = JSONObject.parseObject(body,Map.class);
    Set set = map.keySet();
    for(String s : set){
        System.out.println(map.get(s).toString());
        postMethod.addParameter(s,map.get(s).toString());
    }
    try {
        //执行post请求
        httpClient.executeMethod(postMethod);
        //可以对响应回来的报文进行处理
        mesg = postMethod.getResponseBodyAsString();
        System.out.printf(mesg);
    } catch (HttpException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }finally{
        //关闭连接释放资源的方法
        postMethod.releaseConnection();
        //((SimpleHttpConnectionManager)httpClient.getHttpConnectionManager()).shutdown();
        httpClient.getHttpConnectionManager().closeIdleConnections(0);
    }
    return mesg;
}

}
`