java - bean 和 Jackson 库的问题

Question

嗨!

我正在处理 .json 文件，如下所示:

[{  
  "SourceFile": "videos/KobeAlleyOop.flv",  
  "ExifTool": {  
    "ExifToolVersion": 8.22,  
    "Warning": "Truncated 'mdat' data"  
  },  
  "System": {  
    "FileName": "KobeAlleyOop.flv",  
    "Directory": "videos",  
    "FileSize": "4.8 MB",  
    "FileModifyDate": "2010:06:15 14:57:24+02:00",  
    "FilePermissions": "rwxr-xr-x"  
  },  
  "File": {  
    "FileType": "MP4",  
    "MIMEType": "video/mp4"  
  }]  

我制作了一个包含 3 个组件的 Bean:

 public class MetadataContentBean {   
 SourceFileBean sourceFileBean;  
     FileBean fileBean;    
     SystemBean systemBean;   

     public FileBean getFileBean() {   return fileBean;  }   
 @JsonProperty("File")    
public void setFileBean(FileBean fileBean) {    
 this.fileBean = fileBean;    }   
 public SystemBean getSystemBean() {   
 return systemBean;    }   
 @JsonProperty("System")    
public void setSystemBean(SystemBean systemBean) {
 this.systemBean = systemBean;    }   
 public SourceFileBean
 getSourceFileBean() {    
 sourceFileBean.getSource();     return
 sourceFileBean;    }     
 @JsonProperty("SourceFile")    
public void setSourceFileBean(SourceFileBean
 sourceFileBean) {    
 this.sourceFileBean = sourceFileBean; 
 }   }

并且我添加了一个SourceFileBean的例子，其他类似:

public class SourceFileBean {

 private String source;
 public String getSource() {
  return source;
 }
 @JsonProperty("SourceFile")
 public void setSource(String source) {
  this.source = source;
 }
}

在主程序中我调用了:

InputStream is = this.getClass().getClassLoader().getResourceAsStream(filename);  
    String jsonTxt = IOUtils.toString(is);  
    JSONArray json = (JSONArray) JSONSerializer.toJSON(jsonTxt);  
    JSONObject metadatacontent = json.getJSONObject(0);  
    ObjectMapper mapper = new ObjectMapper();  mapper.readValue(metadatacontent.toString(),MetadataContentBean.class);

但是我运行的时候出现这个错误，我不知道为什么:

org.codehaus.jackson.map.JsonMappingException: Can not construct instance of com.path.bean.SourceFileBean, problem: no suitable creator method found at [Source: java.io.StringReader@12d7a10; line: 1, column: 2] at org.codehaus.jackson.map.JsonMappingException.from(JsonMappingException.java:159) at org.codehaus.jackson.map.deser.StdDeserializationContext.instantiationException(StdDeserializationContext.java:212) at org.codehaus.jackson.map.deser.BeanDeserializer.deserializeFromString(BeanDeserializer.java:415) at org.codehaus.jackson.map.deser.BeanDeserializer.deserialize(BeanDeserializer.java:291) at org.codehaus.jackson.map.deser.SettableBeanProperty.deserialize(SettableBeanProperty.java:135) at org.codehaus.jackson.map.deser.SettableBeanProperty$MethodProperty.deserializeAndSet(SettableBeanProperty.java:221) at org.codehaus.jackson.map.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:390) at org.codehaus.jackson.map.deser.BeanDeserializer.deserialize(BeanDeserializer.java:286) at org.codehaus.jackson.map.ObjectMapper._readMapAndClose(ObjectMapper.java:1588) at org.codehaus.jackson.map.ObjectMapper.readValue(ObjectMapper.java:1116) at com.path.parser.JSon.Parser(JSon.java:65) at com.path.parser.JSon.main(JSon.java:29)

有什么帮助吗？提前致谢!

Answer 1

我猜这只是因为您的 JSON 表示一个数组，其中包含一个对象。您要求 Jackson 将此数组数据反序列化到 MetadataContentBean 的单个实例中，这是它做不到的。

尝试从 JSOn 周围移除 [] 括号，然后重试。