将JSON响应转换为Java对象

Question

我需要将JSON响应转换为Java对象，但我却是nullpointerException。 这是我的模型课：

public class Cheque {

private String payeeName;
private String accountNumber;
private String ifsCode;
private String micr;
private String bankName;

public Cheque() {
    super();
    // TODO Auto-generated constructor stub
}

public Cheque(String payeeName, String accountNumber, String ifsCode, String micr, String bankName) {
    super();
    this.payeeName = payeeName;
    this.accountNumber = accountNumber;
    this.ifsCode = ifsCode;
    this.micr = micr;
    this.bankName = bankName;
}


public String getPayeeName() {
    return payeeName;
}

public void setPayeeName(String payeeName) {
    this.payeeName = payeeName;
}

public String getAccountNumber() {
    return accountNumber;
}

public void setAccountNumber(String accountNumber) {
    this.accountNumber = accountNumber;
}

public String getIfsCode() {
    return ifsCode;
}

public void setIfscCode(String ifsCode) {
    this.ifsCode = ifsCode;
}

public String getMicr() {
    return micr;
}

public void setMicr(String micr) {
    this.micr = micr;
}

public String getBankName() {
    return bankName;
}

public void setBankName(String bankName) {
    this.bankName = bankName;
}

在下面，我发布了调用Python程序并从中获取Json响应的方法：

public class RunPython {

public static void main(String[] args) throws IOException,ScriptException,NullPointerException{
    // TODO Auto-generated method stub
    Process p = Runtime.getRuntime().exec("python <path to file>/reg.py");
    BufferedReader in = new BufferedReader(new InputStreamReader(p.getInputStream()));
    String line ;
    try {
        while((line =in.readLine()) != null) {
            System.out.println(line);
        }
   } finally {
     in.close();
   }

    ObjectMapper mapper = new ObjectMapper();
    try { 

        Cheque cheque = mapper.readValue(line, Cheque.class); 
        System.out.println("Java object :"); 
        System.out.println(cheque); 
        }
    catch (JsonGenerationException ex) { 
        ex.printStackTrace(); 
        } 
    catch (JsonMappingException ex) {
        ex.printStackTrace(); 
        } 
    catch (IOException ex) { 
        ex.printStackTrace(); 
        }}}

我得到的JSON响应是：

{
"bankName": [
    "Bank"
],
"accountNumber": [
    "989898989898"
],
"ifsCode": [
    "0000000"
],
"micr": [
    "0000000"
],
"payeeName": [
    "name"
]

}

运行该程序后，我得到了预期的JSON响应，但是在将其转换为Java对象时，它在主线程中显示了nullPointerException。 帮助我找出错误所在。

Answer 1

在打印时，您在这里消耗/耗尽所有Process Inputstream：

 try {
        while((line =in.readLine()) != null) {
            System.out.println(line);
        }

后来当您调用下面的内容时，它已经是null了：

Cheque cheque = mapper.readValue(line, Cheque.class); 

您必须在上述while循环中处理它，而不是仅将其打印出来

Answer 2

当您到达以下语句时：

    Cheque cheque = mapper.readValue(line, Cheque.class); 

可变line null。

因此，您既可以使用StringBuilder重建JSON字符串，也可以删除打印响应的代码，然后直接从p.getInputStream()解析JSON。

Answer 3

您的Java对象具有String值，但是JSON具有数组类型（[]）