傑克遜ResourceAccessException：I/O錯誤：無法識別領域

Question

我有了這個JSON文件

[ 
    { 
     "foo":{ 
     "comment":null, 
     "media_title":"How I Met Your Mother", 
     "user_username":"nani" 
     } 
    }, 
    { 
     "foo":{ 
     "comment":null, 
     "media_title":"Family Guy", 
     "user_username":"nani" 
     } 
    } 
] 

所以這是富實體的陣列。

然後，我有我的Foo對象：

import org.codehaus.jackson.annotate.JsonProperty; 
    import org.codehaus.jackson.map.annotate.JsonRootName; 

    @JsonRootName("foo") 
    public class Foo { 

     @JsonProperty 
     String comment; 
     @JsonProperty("media_title") 
     String mediaTitle; 
     @JsonProperty("user_username") 
     String userName; 

/** setters and getters go here **/ 

    } 

然後我有我我FooTemplate如下：

public List<Foo> getFoos() { 
    return java.util.Arrays.asList(restTemplate.getForObject(buildUri("/foos.json"), 
      Foo[].class)); 
} 

但是當我運行我的簡單測試，我得到：

org.springframework.web.client.ResourceAccessException: I/O error: Unrecognized field "foo" (Class org.my.package.impl.Foo), not marked as ignorable at [Source: java.io.ByteArrayInputStream@554d7745; line: 3, column: 14] (through reference chain: org.my.package.impl.Foo["foo"]); 

Answer 1

Exception表明它試圖反序列化JSONObject（第th at是頂級JSONArray）的元素轉換爲Foo對象。因此，您沒有一個Foo實體數組，您有一個具有Foo成員的對象數組。

這裏是什麼ObjectMapper正在試圖做的事：

[ 
    {   <---- It thinks this is a Foo. 
     "foo":{ <---- It thinks this is a member of a Foo. 
     "comment":null, 
     "media_title":"How I Met Your Mother", 
     "user_username":"nani" 
     } 
    }, 
    {   <---- It thinks this is a Foo. 
     "foo":{ <---- It thinks this is a member of a Foo. 
     "comment":null, 
     "media_title":"Family Guy", 
     "user_username":"nani" 
     } 
    } 
] 

正是因爲這一點的Exception抱怨

Unrecognized field "foo" (Class org.my.package.impl.Foo)

也許你想取出第一JSONObject，和擺脫foo標識符。

[ 
    { 
     "comment":null, 
     "media_title":"How I Met Your Mother", 
     "user_username":"nani" 
    }, 
    { 
     "comment":null, 
     "media_title":"Family Guy", 
     "user_username":"nani" 
    } 
] 

編輯

您也可以創建一個新的Bar對象，將舉行一個Foo實例，並試圖來解讀到一個數組。

class Bar { 
    @JsonProperty 
    private Foo foo; 

    // setter/getter 
} 

public List<Bar> getBars() { 
    return java.util.Arrays.asList(restTemplate.getForObject(buildUri("/foos.json"), 
      Bar[].class)); 
}