Java - 解析 JSON 有效负载，省略数组中损坏的对象

Question

将 JSON 负载解析为 POJO 时是否可以省略损坏的对象？

示例有效负载:

[
     {
        "someField": "this_object_seems_to_be_ok"
     },
     { 
        "someBrokenStructure"= "equals_sign_instead_of_colon_here"
     }
]

我想获取只有一个结构正确的对象的列表。现有的框架可以实现吗？

Answer 1

为无效的 JSON 有效负载编写反序列化器在所有情况下都获得预期结果确实很困难。具有许多嵌套 JSON 对象和 JSON 数组的 JSON 有效负载可以通过多种方式进行破坏。在您的情况下，它的结构非常简单，并且应该易于维护。

因此，您需要实现自定义 List 反序列化器，如下所示:

import com.fasterxml.jackson.core.JsonParseException;
import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.core.JsonToken;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.JsonDeserializer;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.module.SimpleModule;
import com.fasterxml.jackson.databind.type.MapType;

import java.io.File;
import java.io.IOException;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class JsonApp {

    public static void main(String[] args) throws Exception {
        File jsonFile = new File("./src/main/resources/test.json");

        SimpleModule skipInvalidObjectsModule = new SimpleModule();
        skipInvalidObjectsModule.addDeserializer(List.class, new ListJsonDeserializer());

        ObjectMapper mapper = new ObjectMapper();
        mapper.registerModule(skipInvalidObjectsModule);

        List<Map<String, Object>> result = mapper.readValue(jsonFile, List.class);
        System.out.println(result);
    }
}

class ListJsonDeserializer extends JsonDeserializer<List<Object>> {

    @Override
    public List<Object> deserialize(JsonParser p, DeserializationContext ctxt) throws IOException {
        MapType mapType = ctxt.getTypeFactory().constructMapType(HashMap.class, String.class, Object.class);
        JsonDeserializer<Object> mapDeserializer = ctxt.findRootValueDeserializer(mapType);

        List<Object> result = new ArrayList<>();

        p.nextToken();
        while (p.currentToken() != JsonToken.END_ARRAY) {
            if (p.currentToken() == JsonToken.START_OBJECT) {
                try {
                    result.add(mapDeserializer.deserialize(p, ctxt));
                } catch (JsonParseException e) {
                    System.err.println(e.getMessage());
                }
            }
            try {
                p.nextToken();
            } catch (JsonParseException e) {
                System.err.println(e.getMessage());
            }
        }

        return result;
    }
}

上面的代码打印第一个错误:

Unexpected character ('=' (code 61)): was expecting a colon to separate field name and value
 at [Source: (File); line: 6, column: 27]
Unexpected character ('"' (code 34)): was expecting comma to separate Object entries
 at [Source: (File); line: 6, column: 29]
Unexpected character ('e' (code 101)): was expecting comma to separate Object entries
 at [Source: (File); line: 6, column: 30]
Unexpected character ('q' (code 113)): was expecting comma to separate Object entries
 at [Source: (File); line: 6, column: 31]
Unexpected character ('u' (code 117)): was expecting comma to separate Object entries
 at [Source: (File); line: 6, column: 32]
Unexpected character ('a' (code 97)): was expecting comma to separate Object entries
 at [Source: (File); line: 6, column: 33]
Unexpected character ('l' (code 108)): was expecting comma to separate Object entries
 at [Source: (File); line: 6, column: 34]
Unexpected character ('s' (code 115)): was expecting comma to separate Object entries
 at [Source: (File); line: 6, column: 35]
Unexpected character ('_' (code 95)): was expecting comma to separate Object entries
 at [Source: (File); line: 6, column: 36]
Unexpected character ('s' (code 115)): was expecting comma to separate Object entries
 at [Source: (File); line: 6, column: 37]
Unexpected character ('i' (code 105)): was expecting comma to separate Object entries
 at [Source: (File); line: 6, column: 38]
Unexpected character ('g' (code 103)): was expecting comma to separate Object entries
 at [Source: (File); line: 6, column: 39]
Unexpected character ('n' (code 110)): was expecting comma to separate Object entries
 at [Source: (File); line: 6, column: 40]
Unexpected character ('_' (code 95)): was expecting comma to separate Object entries
 at [Source: (File); line: 6, column: 41]
Unexpected character ('i' (code 105)): was expecting comma to separate Object entries
 at [Source: (File); line: 6, column: 42]
Unexpected character ('n' (code 110)): was expecting comma to separate Object entries
 at [Source: (File); line: 6, column: 43]
Unexpected character ('s' (code 115)): was expecting comma to separate Object entries
 at [Source: (File); line: 6, column: 44]
Unexpected character ('t' (code 116)): was expecting comma to separate Object entries
 at [Source: (File); line: 6, column: 45]
Unexpected character ('e' (code 101)): was expecting comma to separate Object entries
 at [Source: (File); line: 6, column: 46]
Unexpected character ('a' (code 97)): was expecting comma to separate Object entries
 at [Source: (File); line: 6, column: 47]
Unexpected character ('d' (code 100)): was expecting comma to separate Object entries
 at [Source: (File); line: 6, column: 48]
Unexpected character ('_' (code 95)): was expecting comma to separate Object entries
 at [Source: (File); line: 6, column: 49]
Unexpected character ('o' (code 111)): was expecting comma to separate Object entries
 at [Source: (File); line: 6, column: 50]
Unexpected character ('f' (code 102)): was expecting comma to separate Object entries
 at [Source: (File); line: 6, column: 51]
Unexpected character ('_' (code 95)): was expecting comma to separate Object entries
 at [Source: (File); line: 6, column: 52]
Unexpected character ('c' (code 99)): was expecting comma to separate Object entries
 at [Source: (File); line: 6, column: 53]
Unexpected character ('o' (code 111)): was expecting comma to separate Object entries
 at [Source: (File); line: 6, column: 54]
Unexpected character ('l' (code 108)): was expecting comma to separate Object entries
 at [Source: (File); line: 6, column: 55]
Unexpected character ('o' (code 111)): was expecting comma to separate Object entries
 at [Source: (File); line: 6, column: 56]
Unexpected character ('n' (code 110)): was expecting comma to separate Object entries
 at [Source: (File); line: 6, column: 57]
Unexpected character ('_' (code 95)): was expecting comma to separate Object entries
 at [Source: (File); line: 6, column: 58]
Unexpected character ('h' (code 104)): was expecting comma to separate Object entries
 at [Source: (File); line: 6, column: 59]
Unexpected character ('e' (code 101)): was expecting comma to separate Object entries
 at [Source: (File); line: 6, column: 60]
Unexpected character ('r' (code 114)): was expecting comma to separate Object entries
 at [Source: (File); line: 6, column: 61]
Unexpected character ('e' (code 101)): was expecting comma to separate Object entries
 at [Source: (File); line: 6, column: 62]
Unexpected character ('"' (code 34)): was expecting comma to separate Object entries
 at [Source: (File); line: 6, column: 63]

最终结果:

[{someField=this_object_seems_to_be_ok}]