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我使用Grails中的Jackson庫來解析JSON對象，JSON對象中的一個鍵（來自InputStream）是hot_regions，其值是一個JSON對象數組：使用Jackson解析JSON對象數組
String regionsJsonStr = "{
"hot_regions" : [
{"region_code_1" : "America"},
{"region_code_2" : "Europe"},
{"region_code_3" : "Asia"}
]
}"
下面是嘗試使用傑克遜解析陣列Java代碼的一部分：
ObjectMapper mapper = new ObjectMapper();
JsonNode root = mapper.readTree(regionsJsonStr);
JsonNode hotRegions = root.path("hot_regions");
TypeReference<List<Region>> regionRef = new TypeReference<List<Region>>(){};
List<Region> regions = mapper.readValue(hotRegions.traverse(), regionRef);
區域被定義爲一個內部類：
private class Region {
private String regionCode;
private String regionName;
public Region() {}
public Region(String code, String name) {
this.regionCode = code;
this.regionName = name;
}
}
這不起作用，Grails報告以下錯誤，我想知道是什麼原因導致錯誤。謝謝
No suitable constructor found for type [simple type, class com.company.RegionService$Region]: can not instantiate from JSON object (need to add/enable type information?)
at [Source: N/A; line: -1, column: -1]. Stacktrace follows:
com.fasterxml.jackson.databind.JsonMappingException: No suitable constructor found for type [simple type, class com.company.RegionService$Region]: can not instantiate from JSON object (need to add/enable type information?)
at [Source: N/A; line: -1, column: -1]
at com.fasterxml.jackson.databind.JsonMappingException.from(JsonMappingException.java:164)
at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObjectUsingNonDefault(BeanDeserializer.java:400)
at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:289)
at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:121)
at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:226)
at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:203)
at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:23)
at com.fasterxml.jackson.databind.ObjectMapper._readValue(ObjectMapper.java:2768)
at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:1492)
at com.company.RegionService.getRegions(RegionService.groovy:48)
at com.company.SearchController.getRegions(SearchController.groovy:374)
at grails.plugin.cache.web.filter.PageFragmentCachingFilter.doFilter(PageFragmentCachingFilter.java:200)
at grails.plugin.cache.web.filter.AbstractFilter.doFilter(AbstractFilter.java:63)
at grails.plugin.springsecurity.web.filter.GrailsAnonymousAuthenticationFilter.doFilter(GrailsAnonymousAuthenticationFilter.java:53)
at grails.plugin.springsecurity.web.authentication.RequestHolderAuthenticationFilter.doFilter(RequestHolderAuthenticationFilter.java:49)
at grails.plugin.springsecurity.web.authentication.logout.MutableLogoutFilter.doFilter(MutableLogoutFilter.java:82)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)