如何将已解析的JSON的Java列表解析为Big JSON? [英] How to parse a Java List of already parsed JSON into a Big JSON?

问题描述

我使用Jackson到serialize/deserialize JSON.

我有一个List<String>，其中所有内部元素已经以JSON格式serialized.我想从该List生成一个大的JSON.

I have a List<String> in which all elements inside are already serialized in JSON format. I would like to generate a big JSON from that List.

换句话说，我有:

List<String> a = new ArrayList<>();
a[0] = JSON_0
a[1] = JSON_1
...
a[N] = JSON_N

我想渲染:

[
   {JSON_0},
   {JSON_1},
   ...
   {JSON_N}
]

使用Jackson的最佳方法是什么?

What is the best way to do so using Jackson?

推荐答案

可能更简单的解决方案是创建ArrayNode并使用

Probably the simpler solution would be to create ArrayNode and use addRawValue method:

import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.node.ArrayNode;
import com.fasterxml.jackson.databind.util.RawValue;

public class JsonApp {

    public static void main(String[] args) throws Exception {
        ObjectMapper mapper = new ObjectMapper();

        ArrayNode nodes = mapper.getNodeFactory().arrayNode();
        nodes.addRawValue(new RawValue("{}"));
        nodes.addRawValue(new RawValue("true"));
        nodes.addRawValue(new RawValue("{\"id\":1}"));

        System.out.println(mapper.writeValueAsString(nodes));
    }
}

上面的代码显示:

[{},true,{"id":1}]

您也可以使用列表创建POJO并使用@JsonRawValue批注.但是，如果您没有多余的根对象，则需要为其实现自定义序列化程序. POJO和自定义序列化程序的示例:

You can also, create a POJO with list and use @JsonRawValue annotation. But if you can not have extra root object you need to implement custom serialiser for it. Example with POJO and custom serialiser:

import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.databind.JsonSerializer;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializerProvider;
import com.fasterxml.jackson.databind.annotation.JsonSerialize;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

public class JsonApp {

    public static void main(String[] args) throws Exception {
        ObjectMapper mapper = new ObjectMapper();

        List<String> jsons = new ArrayList<>();
        jsons.add("{}");
        jsons.add("true");
        jsons.add("{\"id\":1}");

        RawJsons root = new RawJsons();
        root.setJsons(jsons);
        System.out.println(mapper.writeValueAsString(root));
    }
}

@JsonSerialize(using = RawJsonSerializer.class)
class RawJsons {

    private List<String> jsons;

    public List<String> getJsons() {
        return jsons;
    }

    public void setJsons(List<String> jsons) {
        this.jsons = jsons;
    }
}

class RawJsonSerializer extends JsonSerializer<RawJsons> {

    @Override
    public void serialize(RawJsons value, JsonGenerator gen, SerializerProvider serializers) throws IOException {
        gen.writeStartArray();
        if (value != null && value.getJsons() != null) {
            for (String json : value.getJsons()) {
                gen.writeRawValue(json);
            }
        }
        gen.writeEndArray();
    }
}

如果需要为数组中的所有项目启用SerializationFeature.INDENT_OUTPUT功能，则需要对所有内部对象进行反序列化，然后再次对其进行序列化.

If you need to have SerializationFeature.INDENT_OUTPUT feature enabled for all items in array, you need to deserialise all inner objects and serialise them again.

另请参阅:

• 如何在其中包含原始JSON使用杰克逊的物体?
• 使用杰克逊处理原始JSON值

• How can I include raw JSON in an object using Jackson?
• Handling raw JSON values using Jackson

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