gson flat json到嵌套对象需要序列化器/解串器吗？

Question

我有一些JSON进来(我没有任何控制或能力来改变JSON中的结构和/或命名...这个问题中要记住这一点很重要),它具有类似于此的"扁平"结构:

{
  "name": "...",
  "email": "...",
  "box_background_color": "...",
  "box_border_color": "...",
  "box_text_color": "...",
  ...
}

现在,我可以创建一个简单的对象来保持一切平坦,如下所示:

public class Settings {

  @SerializedName("name")
  private String _name;

  @SerializedName("email")
  private String _emailAddress;

  @SerializedName("box_background_color")
  private String _boxBackgroundColor;

  @SerializedName("box_border_color")
  private String _boxBorderColor;

  @SerializedName("box_text_color")
  private String _boxTextColor;

  ...
}

但是,我希望与box设置相关的所有内容都在它自己的类(BoxSettings)中.这更像我想要的:

public class Settings {

  @SerializedName("name")
  private String _name;

  @SerializedName("email")
  private String _emailAddress;

  private BoxSettings _boxSettings

  ...
}

public class BoxSettings {

  @SerializedName("box_background_color")
  private String _boxBackgroundColor;

  @SerializedName("box_border_color")
  private String _boxBorderColor;

  @SerializedName("box_text_color")
  private String _boxTextColor;

  ...
}

我知道如果JSON的结构使得盒子设置是嵌套的,那么很容易实现我想要的,但是,我没有能力改变JSON的结构,所以请不要建议(如果可以,我会这样做).

我的问题是:创建一个完整的TypeAdapter 是实现我想要的唯一方法,还是我仍然可以通过注释完成大部分工作？如果不是唯一的方法,我怎么能在不改变JSON的情况下完成这个呢？

以下是"创建整个TypeAdapter"的含义示例:

public class SettingsTypeAdapter implements JsonDeserializer<Settings>, JsonSerializer<Settings> {

  @Override
  public JsonElement serialize(Settings src, Type typeOfSrc, JsonSerializationContext context) {
    // Add _name
    // Add _emailAddress
    // Add BoxSettings._boxBackgroundColor
    // Add BoxSettings._boxBorderColor
    // Add BoxSettings._boxTextColor
    return jsonElement;
  }

  @Override
  public Settings deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
    // Read _name
    // Read _emailAddress
    // Read BoxSettings._boxBackgroundColor
    // Read BoxSettings._boxBorderColor
    // Read BoxSettings._boxTextColor
    return settings;
  }
}

Answer 1

TypeAdapter 不是唯一的方法，但在这种情况下将是最好的方法，因为您可以将适配器与 Gson 实例（或您正在使用的任何库）关联起来，并将所有映射代码放在那里。

另一种方法是使用JAVA反射。我之前在我的项目中使用过以下代码的一个版本，但从未使用过 JSON，也从未使用过嵌套对象（主要是在没有其他选择的情况下，或者如果我想将 SQL 结果集映射到 Java 对象而不调用resultSet.get...大量次）。

在这种情况下这将起作用。

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import java.lang.reflect.Field;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;

import org.json.JSONObject;

public class Main {

    public static void main(String[] args) {

        try {
            String json = "{\"name\": \"test name\", \"email\": \"email@email.com\", \"box_background_color\": \"red\", \"box_border_color\": \"orange\", \"box_text_color\": \"white\", \"test3_var2\":3}";

            JSONObject jsonObject = new JSONObject(json);

            System.out.println(jsonObject);
            System.out.println();

            /*
             * need to parse JSON into a map of String, Object
             */

            Map<String, Object> mapAll = new HashMap<String, Object>();
            Iterator<String> iter = jsonObject.keys();

            while (iter.hasNext()) {
                String key = (String) iter.next();
                Object value = jsonObject.get(key);

                mapAll.put(key, value);

                System.out.println(key + "::::" + value);
            }

            System.out.println();

            /*
             * use the mapper to generate the objects
             */

            MyMapper<TestClass1> myMapper = new MyMapper<TestClass1>();
            TestClass1 result = myMapper.mapToObject(mapAll, TestClass1.class);

            System.out.println(result);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

    class MyMapper<T> {

        @SuppressWarnings("unchecked")
        public T mapToObject(Map<String, Object> flatStructure, Class<T> objectClass) {
            T result = null;
            Field[] fields = null;

            try {
                // new base object
                result = objectClass.newInstance();

                // get all of its fields
                fields = objectClass.getDeclaredFields();

                for (Field field : fields) {
                    // normal variable
                    if (field.isAnnotationPresent(MyColumn.class)) {
                        String variableKey = field.getAnnotation(MyColumn.class).variableKey();

                        setJavaFieldValue(result, field.getName(), flatStructure.get(variableKey));
                    } 
                    // variable that is an object and itself has to be mapped
                    else if (field.isAnnotationPresent(MyInnerColumn.class)) {
                        String startsWith = field.getAnnotation(MyInnerColumn.class).startsWith();

                        // reduce the map to only have attributes that are related to this field
                        Map<String, Object> reducedMap = reduceMap(startsWith, flatStructure);

                        // make sure that there are attributes for the inner object
                        if (reducedMap != null) {
                            // map the inner object
                            MyMapper<T> myMapper = new MyMapper<T>();
                            T t2 = myMapper.mapToObject(reducedMap, (Class<T>) field.getType());

                            // set the mapped object to the base objecct
                            setJavaFieldValue(result, field.getName(), t2);
                        }
                    } else {
                        // no annotation on the field so ignored
                    }
                }
            } catch (Exception e) {
                e.printStackTrace();
            }

            return result;
        }

        private Map<String, Object> reduceMap(String startsWith, Map<String, Object> mapToReduce) {
            Map<String, Object> result = new HashMap<String, Object>();

            for (Map.Entry<String, Object> entry : mapToReduce.entrySet()) {
                if (entry.getKey().toLowerCase().startsWith(startsWith.toLowerCase())) {
                    result.put(entry.getKey(), entry.getValue());
                }
            }

            return result.size() == 0 ? null : result;
        }

        private void setJavaFieldValue(Object object, String fieldName, Object fieldValue) {
            try {
                Field field = object.getClass().getDeclaredField(fieldName);

                boolean fieldAccess = field.isAccessible();

                // make the field accessible
                field.setAccessible(true);
                field.set(object, fieldValue);

                // put it back to the way it was
                field.setAccessible(fieldAccess);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

    /*
     * Annotation for a regular variable / field
     */
    @Target(ElementType.FIELD)
    @Retention(RetentionPolicy.RUNTIME)
    @interface MyColumn {

        // the variable's JSON key
        String variableKey() default "";
    }

    /*
     * Annotation for an inner / nested variable / field
     */
    @Target(ElementType.FIELD)
    @Retention(RetentionPolicy.RUNTIME)
    @interface MyInnerColumn {

        /*
         *  JSON keys that start with this string will be 
         *  associated with this nested field
         */
        String startsWith() default "";
    }

    class TestClass1 {
        @MyColumn(variableKey = "name")
        private String _name;

        @MyColumn(variableKey = "email")
        private String _emailAddress;

        @MyInnerColumn(startsWith = "box_")
        private TestClass2 innerClass;

        @MyInnerColumn(startsWith = "test3_")
        private TestClass3 innerClass2;

        @Override
        public String toString() {
            return "TestClass1 [_name=" + _name + ", _emailAddress=" + _emailAddress + ", innerClass=" + innerClass + ", innerClass2=" + innerClass2 + "]";
        }
    }

    class TestClass2 {
        @MyColumn(variableKey = "box_background_color")
        private String _boxBackgroundColor;

        @MyColumn(variableKey = "box_border_color")
        private String _boxBorderColor;

        @MyColumn(variableKey = "box_text_color")
        private String _boxTextColor;

        @Override
        public String toString() {
            return "TestClass2 [_boxBackgroundColor=" + _boxBackgroundColor + ", _boxBorderColor=" + _boxBorderColor
                    + ", _boxTextColor=" + _boxTextColor + "]";
        }
    }

    class TestClass3 {
        @MyColumn(variableKey = "test3_var1")
        private String _test3Var1;

        @MyColumn(variableKey = "test3_var2")
        private int _test3Var2;

        @Override
        public String toString() {
            return "TestClass3 [_test3Var1=" + _test3Var1 + ", _test3Var2=" + _test3Var2 + "]";
        }
    }

输出

{"box_background_color":"red","box_text_color":"white","test3_var2":3,"name":"test name","email":"email@email.com","box_border_color":"orange"}

box_background_color::::red
box_text_color::::white
test3_var2::::3
name::::test name
email::::email@email.com
box_border_color::::orange

TestClass1 [_name=test name, _emailAddress=email@email.com, innerClass=TestClass2 [_boxBackgroundColor=red, _boxBorderColor=orange, _boxTextColor=white], innerClass2=TestClass3 [_test3Var1=null, _test3Var2=3]]