Spring Boot - 将 JSON 转换为 JAVA

Posted 2023-02-27

【中文标题】Spring Boot - 将 JSON 转换为 JAVA

【英文标题】：Springboot - convert JSON to JAVA

【发布时间】：2019-04-19 21:21:49

【问题描述】：

我需要从 rest API 获取货币汇率到我的 spring boot 应用程序，并将 JSON 响应转换为 Java 类。 API 会给我如下响应：-

    "USD_INR": 
        "val": 71.884966
    

代码如下：

@RestController
public class MainController 

  @Autowired
  private RestTemplate restTemplate;

  @GetMapping("/hello")
  public float hello()

     ExchangeRate exchangeRate = restTemplate.getForObject("https://free.currencyconverterapi.com/api/v6/convert?q=Source_Target&compact=y",ExchangeRate.class);
     return exchangeRate.getSource_Target().getVal();
  

-

@JsonIgnoreProperties(ignoreUnknown = true)
public class ExchangeRate 
Source_Target SourceTargetObject;

  public Source_Target getSource_Target() 
      return SourceTargetObject;
  


  public void setSource_Target(Source_Target SourceTargetObject) 
      this.SourceTargetObject = SourceTargetObject;
  



@JsonIgnoreProperties(ignoreUnknown = true)
public class Source_Target 
private float val;

  public float getVal() 
    return val;
  

  public void setVal(float val) 
    this.val = val;
  

执行 REST 调用后，我得到空异常。什么都没有返回。我无法在这里弄清楚这个问题。请帮忙

【问题讨论】：

您能否将确切的NullPointerException 堆栈跟踪发布到您的问题？

【参考方案1】：

您可以使用jsonscheme2pojo 轻松地从 json 生成 java bean。

JSON：

"USD_INR": 
    "val": 71.884966

对应的Java bean：

-----------------------------------com.example.Example.java-----------------------------------

package com.example;

import java.io.Serializable;
import java.util.HashMap;
import java.util.Map;
import com.fasterxml.jackson.annotation.JsonAnyGetter;
import com.fasterxml.jackson.annotation.JsonAnySetter;
import com.fasterxml.jackson.annotation.JsonIgnore;
import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.annotation.JsonPropertyOrder;

@JsonInclude(JsonInclude.Include.NON_NULL)
@JsonPropertyOrder(
"USD_INR"
)
public class Example implements Serializable


@JsonProperty("USD_INR")
private USDINR uSDINR;
@JsonIgnore
private Map<String, Object> additionalProperties = new HashMap<String, Object>();
private final static long serialVersionUID = -932753391825750904L;

@JsonProperty("USD_INR")
public USDINR getUSDINR() 
return uSDINR;


@JsonProperty("USD_INR")
public void setUSDINR(USDINR uSDINR) 
this.uSDINR = uSDINR;


public Example withUSDINR(USDINR uSDINR) 
this.uSDINR = uSDINR;
return this;


@JsonAnyGetter
public Map<String, Object> getAdditionalProperties() 
return this.additionalProperties;


@JsonAnySetter
public void setAdditionalProperty(String name, Object value) 
this.additionalProperties.put(name, value);


public Example withAdditionalProperty(String name, Object value) 
this.additionalProperties.put(name, value);
return this;



-----------------------------------com.example.USDINR.java-----------------------------------

package com.example;

import java.io.Serializable;
import java.util.HashMap;
import java.util.Map;
import com.fasterxml.jackson.annotation.JsonAnyGetter;
import com.fasterxml.jackson.annotation.JsonAnySetter;
import com.fasterxml.jackson.annotation.JsonIgnore;
import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.annotation.JsonPropertyOrder;

@JsonInclude(JsonInclude.Include.NON_NULL)
@JsonPropertyOrder(
"val"
)
public class USDINR implements Serializable


@JsonProperty("val")
private Double val;
@JsonIgnore
private Map<String, Object> additionalProperties = new HashMap<String, Object>();
private final static long serialVersionUID = -6384976748235176082L;

@JsonProperty("val")
public Double getVal() 
return val;


@JsonProperty("val")
public void setVal(Double val) 
this.val = val;


public USDINR withVal(Double val) 
this.val = val;
return this;


@JsonAnyGetter
public Map<String, Object> getAdditionalProperties() 
return this.additionalProperties;


@JsonAnySetter
public void setAdditionalProperty(String name, Object value) 
this.additionalProperties.put(name, value);


public USDINR withAdditionalProperty(String name, Object value) 
this.additionalProperties.put(name, value);
return this;

【讨论】：

@JsonProperty("USD_INR") - 不能这样给出，因为属性会随着不同的来源和目标货币而变化..

【参考方案2】：

您的 ExchangeRate 类应该是：

@JsonInclude(JsonInclude.Include.NON_NULL)
@JsonIgnoreProperties(ignoreUnknown = true)
public class ExchangeRate 
    @JsonProperty("USD_INR")
    Source_Target SourceTargetObject;

    public Source_Target getSource_Target() 
        return SourceTargetObject;
    

    public void setSource_Target(Source_Target SourceTargetObject) 
        this.SourceTargetObject = SourceTargetObject;
    

那么你的 Source_Target 类应该是：

@JsonInclude(JsonInclude.Include.NON_NULL)
@JsonIgnoreProperties(ignoreUnknown = true)
public class Source_Target 
    @JsonProperty("val")
    private float val;

    public float getVal() 
         return val;
    

    public void setVal(float val) 
        this.val = val;
    

请注意您的类命名约定。我会将 Source_Target 重命名为 SourceTarget 以遵循 Java 命名约定

【讨论】：

@JsonProperty("USD_INR") - 不能这样给出，因为属性会随着不同的来源和目标货币而变化..

【参考方案3】：

您创建一个自定义地图：

public class ExchangeRate extends HashMap<String, ExchangeRateValue> implements Serializable         


public class ExchangeRateValue implements Serializable 

    private float val;

    public float getVal() 
        return val;
    

    public void setVal(float val) 
        this.val = val;
    

然后称呼它：

 ExchangeRate exchangeRate = restTemplate.getForObject("https://free.currencyconverterapi.com/api/v6/convert?q=Source_Target&compact=y", ExchangeRate.class);
 float data = exchangeRate.get("USD_INR").getVal();