java 接口调用问题

Answer 1

It is also possible to easily solve this problem by using fastjson, jackjson and other tools.
The following is my approach. If you think it is not good, please comment.
Create a Batch class with fields batchNo, List<Detail> detail;

public class Batch{

    private String batchNo;
    private List<Detail> detail;
    
    //下面省略Get和Set方法……
}

public class Detail{
    private String contractCode;
    private int repayAmt;
    private String  repayType;
    
        //下面省略Get和Set方法……
}

import org.codehaus.jackson.*; //这里我随便写的，反正就是用JackJson

public class BeanToJson{

    public static void main(String[] args){

        Batch  batch = new Batch();
        batch.setBatchNo("XX_20170120113655");
        Detail detailA = new Detail();
        Detail detailB = new Detail();
    
        detailA.setContractCode("2017012001");
        detailA.setRepayAmt(6600);
        detailA.setRepayType("REPAY");
    
        detailB.setContractCode("2017012002");
        detailB.setRepayAmt(7600);
        detailB.setRepayType("REPAY");
    
        List<Detail> details = new ArrayList<Detail>();
        details.add(detailA);
        details.add(detailB);
        
        batch.setDetail(details);
    
        //上面都是一些设置数据的东西，下面才是要说的

        ObejctMapper mapper = new ObjectMapper();
    
        String s = mapper.writeValueAsString(batch);
    
        // 现在 s 就是楼主想要的格式了。代码纯手打，不保证没有问题，想表达的是方法！
    }
}

If you often want to change Bean into Json, this method is simple and clear.

Answer 2

ArrayList<Map<String,String>> detail = new ArrayList<Map<String,String>>();
Pack a Map in a list

Answer 3

fastjson, you deserve it.