Gson自定义反序列化以生成不同的json输出

Question

我有一个REST Api服务，它给了我以下响应

{
  "took": 3,
  "timed_out": false,
  "_shards": {
    "total": 3,
    "successful": 3,
    "failed": 0
  },
  "hits": {
    "total": 3,
    "max_score": 123,
    "hits": [
      {
        "_index": "123",
        "_type": "bar",
        "_id": "123",
        "_score": 323,
        "_source": {
          "employeeNo": 239,
          "employeeName": "John",
          "employeeRank": 21,
          "employeeNationality": "Indian",
          "employeeNickName": "KingKong"
        }
      },
      {
        "_index": "234",
        "_type": "bar",
        "_id": "124",
        "_score": 324,
        "_source": {
          "employeeNo": 241,
          "employeeName": "Sunny",
          "employeeRank": 19,
          "employeeNickName": "Jakk"
        }
      },
      {
        "_index": "235",
        "_type": "bar",
        "_id": "125",
        "_score": 325,
        "_source": {
          "employeeNo": 251,
          "employeeName": "Pollard",
          "employeeRank": 10
        }
      }
    ]
  },
  "aggregations": {
    "foo": {
      "buckets": [
        {
          "key": 123,
          "doc_count": 123
        }
      ]
    }
  }
}

实际上，我希望json的格式如下所示（应为json）

[
  {
    "employeeNo": 239,
    "employeeName": "John",
    "employeeRank": 21,
    "employeeNationality": "Indian",
    "employeeNickName": "KingKong"
  },
  {
    "employeeNo": 241,
    "employeeName": "Sunny",
    "employeeRank": 19,
    "employeeNickName": "Jakk"
  },
  {
    "employeeNo": 251,
    "employeeName": "Pollard",
    "employeeRank": 10
  }
]

为了实现这一点，我编写了以下代码

List<Map<String, String>> myResults = new ArrayList<Map<String, String>>();
Gson serializer = new GsonBuilder().create(); 
String responseDetails = doHttpPost(urlToQuery, serializer.toJson(requestBody));
Map<String,Object> restResponse = (Map<String,Object>)serializer.fromJson(responseDetails,Object.class);
if(restResponse.containsKey("hits")){
    Map<String, Object> hits = (Map<String, Object>) restResponse.get("hits");
    if(hits.containsKey("hits")) {
        List<Map<String, Object>> hitDetails = (List<Map<String, Object>>) hits.get("hits");
        for (Map<String, Object> hitDetail : hitDetails) {
            Map<String, Object> sources = (Map<String, Object>) hitDetail.get("_source");
            myResults.add(sources);
        }
    }
}

在上面的代码中，我以字符串的形式从REST Api获取响应，并将其放入变量中。此外，我将其反序列化为映射

Map<String,Object> restResponse = (Map<String,Object>)serializer.fromJson(responseDetails,Object.class);

进一步，我迭代它并形成我的预期Json响应。

我的问题是：在这种方法中，为了获得预期的json，我需要再次迭代反序列化的json，并手动形成它。

在反序列化自身的过程中，有没有什么方法可以得到响应json作为fromJson函数的返回。即如下所示

List<Map<String, String>> myResults = serializer.fromJson(responseDetails);

我们可以重写fromJson函数并编写我们自己的自定义反序列化程序来返回列表吗

期待您的建议，甚至其他可以提高性能的方法。

如果需要更多说明，请告诉我

Answer 1

对于REST服务，我通常建议您使用一些JSON到Java模型转换程序/服务，例如JSONUtils（可在Github上获得）

在此转换之后，您将拥有Java模型：

ServiceResult类

import com.fasterxml.jackson.annotation.JsonProperty;

public class ServiceResult {
    @JsonProperty("took")
    public int getTook() {
        return this.took;
    }

    public void setTook(int took) {
        this.took = took;
    }

    int took;

    @JsonProperty("timed_out")
    public boolean getTimed_out() {
        return this.timed_out;
    }

    public void setTimed_out(boolean timed_out) {
        this.timed_out = timed_out;
    }

    boolean timed_out;

    @JsonProperty("_shards")
    public Shards get_shards() {
        return this._shards;
    }

    public void set_shards(Shards _shards) {
        this._shards = _shards;
    }

    Shards _shards;

    @JsonProperty("hits")
    public Hits getHits() {
        return this.hits;
    }

    public void setHits(Hits hits) {
        this.hits = hits;
    }

    Hits hits;

    @JsonProperty("aggregations")
    public Aggregations getAggregations() {
        return this.aggregations;
    }

    public void setAggregations(Aggregations aggregations) {
        this.aggregations = aggregations;
    }

    Aggregations aggregations;

}

碎片类

import com.fasterxml.jackson.annotation.JsonProperty;

public class Shards {
    @JsonProperty("total")
    public int getTotal() {
        return this.total;
    }

    public void setTotal(int total) {
        this.total = total;
    }

    int total;

    @JsonProperty("successful")
    public int getSuccessful() {
        return this.successful;
    }

    public void setSuccessful(int successful) {
        this.successful = successful;
    }

    int successful;

    @JsonProperty("failed")
    public int getFailed() {
        return this.failed;
    }

    public void setFailed(int failed) {
        this.failed = failed;
    }

    int failed;

}

源类别

import com.fasterxml.jackson.annotation.JsonProperty;

public class Source {
    @JsonProperty("employeeNo")
    public int getEmployeeNo() {
        return this.employeeNo;
    }

    public void setEmployeeNo(int employeeNo) {
        this.employeeNo = employeeNo;
    }

    int employeeNo;

    @JsonProperty("employeeName")
    public String getEmployeeName() {
        return this.employeeName;
    }

    public void setEmployeeName(String employeeName) {
        this.employeeName = employeeName;
    }

    String employeeName;

    @JsonProperty("employeeRank")
    public int getEmployeeRank() {
        return this.employeeRank;
    }

    public void setEmployeeRank(int employeeRank) {
        this.employeeRank = employeeRank;
    }

    int employeeRank;

    @JsonProperty("employeeNationality")
    public String getEmployeeNationality() {
        return this.employeeNationality;
    }

    public void setEmployeeNationality(String employeeNationality) {
        this.employeeNationality = employeeNationality;
    }

    String employeeNationality;

    @JsonProperty("employeeNickName")
    public String getEmployeeNickName() {
        return this.employeeNickName;
    }

    public void setEmployeeNickName(String employeeNickName) {
        this.employeeNickName = employeeNickName;
    }

    String employeeNickName;

}

Hits类

import java.util.List;

import com.fasterxml.jackson.annotation.JsonProperty;

public class Hits {
    @JsonProperty("total")
    public int getTotal() {
        return this.total;
    }

    public void setTotal(int total) {
        this.total = total;
    }

    int total;

    @JsonProperty("max_score")
    public int getMax_score() {
        return this.max_score;
    }

    public void setMax_score(int max_score) {
        this.max_score = max_score;
    }

    int max_score;

    @JsonProperty("hits")
    public List<Hit> getHits() {
        return this.hits;
    }

    public void setHits(List<Hit> hits) {
        this.hits = hits;
    }

    List<Hit> hits;

}

击中类

import com.fasterxml.jackson.annotation.JsonProperty;

public class Hit {
    @JsonProperty("_index")
    public String get_index() {
        return this._index;
    }

    public void set_index(String _index) {
        this._index = _index;
    }

    String _index;

    @JsonProperty("_type")
    public String get_type() {
        return this._type;
    }

    public void set_type(String _type) {
        this._type = _type;
    }

    String _type;

    @JsonProperty("_id")
    public String get_id() {
        return this._id;
    }

    public void set_id(String _id) {
        this._id = _id;
    }

    String _id;

    @JsonProperty("_score")
    public int get_score() {
        return this._score;
    }

    public void set_score(int _score) {
        this._score = _score;
    }

    int _score;

    @JsonProperty("_source")
    public Source get_source() {
        return this._source;
    }

    public void set_source(Source _source) {
        this._source = _source;
    }

    Source _source;

}

Foo类

import java.util.List;

import com.fasterxml.jackson.annotation.JsonProperty;

public class Foo {
    @JsonProperty("buckets")
    public List<Bucket> getBuckets() {
        return this.buckets;
    }

    public void setBuckets(List<Bucket> buckets) {
        this.buckets = buckets;
    }

    List<Bucket> buckets;

}

铲斗等级

import com.fasterxml.jackson.annotation.JsonProperty;

public class Bucket {
    @JsonProperty("key")
    public int getKey() {
        return this.key;
    }

    public void setKey(int key) {
        this.key = key;
    }

    int key;

    @JsonProperty("doc_count")
    public int getDoc_count() {
        return this.doc_count;
    }

    public void setDoc_count(int doc_count) {
        this.doc_count = doc_count;
    }

    int doc_count;

}

聚合类

import com.fasterxml.jackson.annotation.JsonProperty;

public class Aggregations {
    @JsonProperty("foo")
    public Foo getFoo() {
        return this.foo;
    }

    public void setFoo(Foo foo) {
        this.foo = foo;
    }

    Foo foo;

}

现在您有了您的ServiceResult模型，您实际上只需要Source模型。您可以使用java集合流提取它，例如：

import java.io.File;
import java.util.List;
import java.util.stream.Collectors;

import org.apache.commons.io.IOUtils;

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;

public class Test {
    public static void main(String[] args) {
        try {

            // String responseDetails = doHttpPost(urlToQuery, serializer.toJson(requestBody));
            // using your json from file
            String responseDetails = new String(IOUtils.toByteArray(new File("test.json").toURI()), "UTF-8");

            Gson serializer = new GsonBuilder().create();
            ServiceResult example = serializer.fromJson(responseDetails, ServiceResult.class);

            // your expected list
            List<Source> sourceList = example.getHits()
                    .getHits()
                    .stream().map(h -> h.get_source())
                    .collect(Collectors.toList());

            // you can just serialize it to json or do whatever you want
            String json = serializer.toJson(sourceList);
            System.out.println(json);

        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}