从firebase中获取Json，因为字符串在java中不起作用 [英] Fetching Json from firebase as string not working in java

问题描述

使用其他的Firebase数据：

控制台中的FireBase数据：

从firebase获取数据的Java代码

  PoolingHttpClientConnectionManager cm = new PoolingHttpClientConnectionManager （）; 
 cm.setMaxTotal（100）; 
 cm.setDefaultMaxPerRoute（100）; 
 httpClient = HttpClients.custom（）
 .setConnectionManager（cm）
 .build（）; 
 CloseableHttpResponse响应; 
试试{
 String url =https://testcustom-a1a4d.firebaseio.com/1719126/1719130/1719121.json?auth=myauthId; 
 HttpGet httpGet = new HttpGet（url）; 
 response = httpClient.execute（httpGet）; 
 HttpEntity entity = response.getEntity（）; 
 SolutionDto solutionDto = objectMapper.readValue（entity.getContent（），SolutionDto.class）; 
 System.out.println（solutionDto）; 
 $ b $ catch（IOException e）{
 log.error（处理请求到fireBase时出错了，e）; 
 
  

java错误：

  com.fasterxml.jackson.databind.JsonMappingException：无法从字符串value（'{testId）实例化类型为[simple type，com.web.dtos.SolutionDto的类的值1719126}）;没有单个字符串的构造函数/工厂方法
 at [Source：org.apache.http.conn.EofSensorInputStream@554083;行：1，列：1] 
在com.fasterxml.jackson.databind.JsonMappingException.from（JsonMappingException.java:148）〜[jackson-databind-2.4.3.jar：2.4.3] 
在com.fasterxml.jackson.databind.DeserializationContext.mappingException（DeserializationContext.java:757）〜[jackson-databind-2.4.3.jar：2.4.3] 
在com.fasterxml.jackson.databind.deser .ValueInstantiator._createFromStringFallbacks（ValueInstantiator.java:277）〜[jackson-databind-2.4.3.jar：2.4.3] 
 at com.fasterxml.jackson.databind.deser.std.StdValueInstantiator.createFromString（StdValueInstantiator。 java：289）〜[jackson-databind-2.4.3.jar：2.4.3] 
 at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.deserializeFromString（BeanDeserializerBase.java:1133）〜[jackson-databind -2.4.3.jar：2.4.3] 
 at com.fasterxml.jackson.databind.deser.BeanDeserializer._deserializeOther（BeanDeserializer.java:135）〜[jackson-databind-2.4.3.jar：2.4。 3] 
在com.fasterxml.jackson.module。 afterburner.deser.SuperSonicBeanDeserializer.deserialize（SuperSonicBeanDeserializer.java:123）〜[jackson-module-afterburner-2.4.3.jar：2.4.3] 
 at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose（ObjectMapper .java：3051）〜[jackson-databind-2.4.3.jar：2.4.3] 
 at com.fasterxml.jackson.databind.ObjectMapper.readValue（ObjectMapper.java:2192）〜[jackson-databind- 2.4.3.jar：2.4.3] 
  

为什么不能解析字符串如何对象？

编辑：
SolutionDto.java

  @JsonInclude（Include.NON_NULL）
 @JsonIgnoreProperties（ignoreUnknown = true）
 public class SolutionDto {
 private long testId; 
 public SolutionDto（）{} 
 public SolutionDto（Long testId）{
 this.testId = testId; 
} 
 public void setTestId（Long testId）{
 this.testId = testId; 
} 
 public Long getTestId（）{
 return testId; 
 
 
 
 
 $ b 
从firebase导出Json：
  {
1719126：{
1719130：{
1719121：{\ testId \：\1719126\}
} 
} 
} 
  
下面的代码可以和上面的solutionDto一起工作，但是当从firebase中使用apache获取时，它是行不通的 
 
 
  String s ={\testId \：\1719126 \}; 
 objectMapper.readValue（s，SolutionDto.class）; 
  
 
 
解决方案
没有单个字符串的构造函数/工厂方法 
 
 
 
您需要提供一个单个字符串构造函数 b 
 $ b 
  public SolutionDto（String data）
  
或按照 @JsonCreator 注释的工厂。 on-deserialize-requests-single-string-constr>  here   
 
Firebase data using rest:


FireBase data in console:

Java code to fetch data from firebase 
PoolingHttpClientConnectionManager cm = new PoolingHttpClientConnectionManager();
        cm.setMaxTotal(100);
        cm.setDefaultMaxPerRoute(100);
        httpClient =  HttpClients.custom()
        .setConnectionManager(cm)               
        .build();
        CloseableHttpResponse response;
        try {
            String url = "https://testcustom-a1a4d.firebaseio.com/1719126/1719130/1719121.json?auth=myauthId";
            HttpGet httpGet = new HttpGet(url);         
            response = httpClient.execute(httpGet);
            HttpEntity entity = response.getEntity();
            SolutionDto solutionDto = objectMapper.readValue(entity.getContent(), SolutionDto.class);
            System.out.println(solutionDto);

        } catch (IOException e) {
            log.error("something went wrong while processing requrest to fireBase", e);         
        }
Error in java:
    com.fasterxml.jackson.databind.JsonMappingException: Can not instantiate value of type [simple type, class com.web.dtos.SolutionDto] from String value ('{"testId":"1719126"}'); no single-String constructor/factory method
 at [Source: org.apache.http.conn.EofSensorInputStream@554083; line: 1, column: 1]
        at com.fasterxml.jackson.databind.JsonMappingException.from(JsonMappingException.java:148) ~[jackson-databind-2.4.3.jar:2.4.3]
        at com.fasterxml.jackson.databind.DeserializationContext.mappingException(DeserializationContext.java:757) ~[jackson-databind-2.4.3.jar:2.4.3]
        at com.fasterxml.jackson.databind.deser.ValueInstantiator._createFromStringFallbacks(ValueInstantiator.java:277) ~[jackson-databind-2.4.3.jar:2.4.3]
        at com.fasterxml.jackson.databind.deser.std.StdValueInstantiator.createFromString(StdValueInstantiator.java:289) ~[jackson-databind-2.4.3.jar:2.4.3]
        at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.deserializeFromString(BeanDeserializerBase.java:1133) ~[jackson-databind-2.4.3.jar:2.4.3]
        at com.fasterxml.jackson.databind.deser.BeanDeserializer._deserializeOther(BeanDeserializer.java:135) ~[jackson-databind-2.4.3.jar:2.4.3]
        at com.fasterxml.jackson.module.afterburner.deser.SuperSonicBeanDeserializer.deserialize(SuperSonicBeanDeserializer.java:123) ~[jackson-module-afterburner-2.4.3.jar:2.4.3]
        at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:3051) ~[jackson-databind-2.4.3.jar:2.4.3]
        at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2192) ~[jackson-databind-2.4.3.jar:2.4.3]
Why it is not able to parse string to object?

EDIT:
SolutionDto.java
@JsonInclude(Include.NON_NULL)
@JsonIgnoreProperties(ignoreUnknown=true)
public class SolutionDto {
    private Long testId;
    public SolutionDto(){}
    public SolutionDto(Long testId) {
       this.testId = testId;
    }
    public void setTestId(Long testId) {
        this.testId = testId;
    }
    public Long getTestId() {
        return testId;
    }
}
Export of Json from firebase:
{
  "1719126" : {
    "1719130" : {
      "1719121" : "{\"testId\":\"1719126\"}"
    }
  }
}
The below code work fine with above solutionDto, but when the same is fetch using apache from firebase it does not work
String s = "{\"testId\":\"1719126\"}";
objectMapper.readValue(s, SolutionDto.class);

解决方案
As your exception says.... no single-String constructor/factory method

You need to provide a single-String constructor i.e:
public SolutionDto(String data)
Or create a factory annotated by @JsonCreator as described here

                        
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