Android Java Serialisierungsbeispiele

// Android Java JSON Serialization Examples
// Using Gson library and JSONObject

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.reflect.TypeToken;
import com.google.gson.ExclusionStrategy;
import com.google.gson.FieldAttributes;
import org.json.JSONObject;
import org.json.JSONArray;
import org.json.JSONException;
import java.lang.reflect.Type;
import java.util.Date;
import java.util.List;
import java.util.Map;

// Data model classes
class User {
    public int id;
    public String username;
    public String email;
    public Integer age;
    public boolean isActive;
    public Date createdAt;

    public User() {}

    public User(int id, String username, String email, Integer age, boolean isActive, Date createdAt) {
        this.id = id;
        this.username = username;
        this.email = email;
        this.age = age;
        this.isActive = isActive;
        this.createdAt = createdAt;
    }
}

class Product {
    public String productId;
    public String name;
    public double price;
    public List<String> tags;
    public boolean inStock;

    public Product() {}

    public Product(String productId, String name, double price, List<String> tags, boolean inStock) {
        this.productId = productId;
        this.name = name;
        this.price = price;
        this.tags = tags;
        this.inStock = inStock;
    }
}

class Order {
    public int orderId;
    public User user;
    public List<Product> products;
    public double totalAmount;
    public String orderDate;

    public Order() {}

    public Order(int orderId, User user, List<Product> products, double totalAmount, String orderDate) {
        this.orderId = orderId;
        this.user = user;
        this.products = products;
        this.totalAmount = totalAmount;
        this.orderDate = orderDate;
    }
}

// 1. Basic JSON Serialization with Gson
class BasicJsonSerializer {
    private Gson gson = new Gson();

    // Serialize simple object
    public String serializeObject(Object obj) {
        String json = gson.toJson(obj);
        System.out.println("Serialized: " + json);
        return json;
    }

    // Serialize with pretty printing
    public String serializeObjectPretty(Object obj) {
        Gson prettyGson = new GsonBuilder()
            .setPrettyPrinting()
            .create();

        String json = prettyGson.toJson(obj);
        System.out.println("Serialized (pretty):\n" + json);
        return json;
    }

    // Serialize null values explicitly
    public String serializeWithNulls(Object obj) {
        Gson gsonWithNulls = new GsonBuilder()
            .serializeNulls()
            .create();

        return gsonWithNulls.toJson(obj);
    }

    // Serialize date in custom format
    public String serializeWithDateFormat(Object obj, String dateFormat) {
        Gson gsonWithDateFormat = new GsonBuilder()
            .setDateFormat(dateFormat)
            .create();

        return gsonWithDateFormat.toJson(obj);
    }

    // Serialize with custom field naming
    public String serializeWithFieldNaming(Object obj) {
        Gson gsonWithLowercase = new GsonBuilder()
            .setFieldNamingPolicy(com.google.gson.FieldNamingPolicy.LOWER_CASE_WITH_UNDERSCORES)
            .create();

        return gsonWithLowercase.toJson(obj);
    }
}

// 2. Serialization with JSONObject
class JSONObjectSerializer {

    // Serialize simple object to JSONObject
    public JSONObject serializeToJsonObject(User user) {
        try {
            JSONObject json = new JSONObject();
            json.put("id", user.id);
            json.put("username", user.username);
            json.put("email", user.email);
            json.put("age", user.age);
            json.put("isActive", user.isActive);
            if (user.createdAt != null) {
                json.put("createdAt", user.createdAt.getTime());
            }
            return json;
        } catch (JSONException e) {
            System.out.println("JSON error: " + e.getMessage());
            return null;
        }
    }

    // Serialize to JSON string
    public String serializeToString(User user) {
        JSONObject json = serializeToJsonObject(user);
        return json != null ? json.toString() : null;
    }

    // Serialize list to JSONArray
    public JSONArray serializeList(List<User> users) {
        JSONArray array = new JSONArray();
        for (User user : users) {
            try {
                JSONObject json = new JSONObject();
                json.put("id", user.id);
                json.put("username", user.username);
                json.put("email", user.email);
                array.put(json);
            } catch (JSONException e) {
                System.out.println("Error: " + e.getMessage());
            }
        }
        return array;
    }
}

// 3. Advanced JSON Serialization
class AdvancedJsonSerializer {

    // Serialize with exclusion strategy
    public String serializeWithExclusion(Object obj) {
        Gson gson = new GsonBuilder()
            .setExclusionStrategies(new ExclusionStrategy() {
                @Override
                public boolean shouldSkipField(FieldAttributes field) {
                    // Skip transient fields
                    return java.lang.reflect.Modifier.isTransient(field.getDeclaringClass());
                }

                @Override
                public boolean shouldSkipClass(Class<?> clazz) {
                    return false;
                }
            })
            .create();

        return gson.toJson(obj);
    }

    // Serialize to file
    public boolean serializeToFile(Object obj, String filePath) {
        try {
            Gson gson = new Gson();
            String json = gson.toJson(obj);

            java.io.FileWriter writer = new java.io.FileWriter(filePath);
            writer.write(json);
            writer.close();

            System.out.println("Serialized to file: " + filePath);
            return true;
        } catch (Exception e) {
            System.out.println("Error serializing to file: " + e.getMessage());
            return false;
        }
    }

    // Serialize with versioning
    public String serializeWithVersion(Object obj, double version) {
        Gson gson = new GsonBuilder()
            .setVersion(version)
            .create();

        return gson.toJson(obj);
    }

    // Serialize HTML-safe
    public String serializeHtmlSafe(Object obj) {
        Gson gson = new GsonBuilder()
            .disableHtmlEscaping()
            .create();

        return gson.toJson(obj);
    }
}

// 4. Collection Serialization
class CollectionSerializer {
    private Gson gson = new Gson();

    // Serialize list
    public String serializeList(List<Object> list) {
        return gson.toJson(list);
    }

    // Serialize map
    public String serializeMap(Map<String, Object> map) {
        return gson.toJson(map);
    }

    // Serialize set
    public String serializeSet(java.util.Set<Object> set) {
        return gson.toJson(set);
    }

    // Serialize nested collections
    public String serializeNested(Map<String, List<Object>> data) {
        return gson.toJson(data);
    }

    // Serialize array
    public String serializeArray(Object[] array) {
        return gson.toJson(array);
    }

    // Serialize list with TypeToken
    public String serializeTypedList(List<User> users) {
        Type userListType = new TypeToken<List<User>>() {}.getType();
        return gson.toJson(users, userListType);
    }
}

// 5. Streaming JSON Serialization
class StreamingJsonSerializer {

    // Serialize using JsonWriter (for large datasets)
    public boolean serializeUsingJsonWriter(List<User> data, String filePath) {
        try {
            java.io.FileWriter writer = new java.io.FileWriter(filePath);
            com.google.gson.stream.JsonWriter jsonWriter = new com.google.gson.stream.JsonWriter(writer);

            jsonWriter.beginArray();
            for (User user : data) {
                jsonWriter.beginObject();

                jsonWriter.name("id").value(user.id);
                jsonWriter.name("username").value(user.username);
                jsonWriter.name("email").value(user.email);
                if (user.age != null) {
                    jsonWriter.name("age").value(user.age);
                }
                jsonWriter.name("isActive").value(user.isActive);

                jsonWriter.endObject();
            }
            jsonWriter.endArray();

            jsonWriter.close();
            writer.close();

            System.out.println("Streamed " + data.size() + " items to " + filePath);
            return true;
        } catch (Exception e) {
            System.out.println("Error streaming JSON: " + e.getMessage());
            return false;
        }
    }

    // Serialize with buffering
    public List<String> serializeWithBuffer(List<Object> data, int bufferSize) {
        List<String> chunks = new java.util.ArrayList<>();
        Gson gson = new Gson();

        for (int i = 0; i < data.size(); i += bufferSize) {
            int end = Math.min(i + bufferSize, data.size());
            List<Object> chunk = data.subList(i, end);
            chunks.add(gson.toJson(chunk));
        }

        return chunks;
    }
}

// 6. Android JSONObject (Built-in)
class BuiltInJsonSerializer {

    // Using Android's built-in JSONObject
    public String serializeWithBuiltIn(User user) {
        try {
            JSONObject json = new JSONObject();
            json.put("id", user.id);
            json.put("username", user.username);
            json.put("email", user.email);
            json.put("age", user.age);
            json.put("isActive", user.isActive);

            return json.toString();
        } catch (JSONException e) {
            System.out.println("JSON error: " + e.getMessage());
            return null;
        }
    }

    // Serialize collection
    public String serializeCollection(List<User> users) {
        try {
            JSONArray array = new JSONArray();
            for (User user : users) {
                JSONObject json = new JSONObject();
                json.put("id", user.id);
                json.put("username", user.username);
                json.put("email", user.email);
                array.put(json);
            }
            return array.toString();
        } catch (JSONException e) {
            System.out.println("Error: " + e.getMessage());
            return null;
        }
    }

    // Serialize map
    public String serializeMap(Map<String, Object> data) {
        try {
            JSONObject json = new JSONObject();
            for (Map.Entry<String, Object> entry : data.entrySet()) {
                json.put(entry.getKey(), entry.getValue());
            }
            return json.toString();
        } catch (JSONException e) {
            System.out.println("Error: " + e.getMessage());
            return null;
        }
    }
}

// Main demonstration
class JsonSerializationDemo {
    public static void demonstrateJsonSerialization() {
        System.out.println("=== Android Java JSON Serialization Examples ===\n");

        // 1. Basic serialization
        System.out.println("--- 1. Basic Serialization ---");
        BasicJsonSerializer basicSerializer = new BasicJsonSerializer();

        User user = new User(1, "alice", "[email protected]", 25, true, new Date());

        String json1 = basicSerializer.serializeObject(user);
        System.out.println("Simple: " + json1);

        // 2. Pretty printing
        System.out.println("\n--- 2. Pretty Printing ---");
        String json2 = basicSerializer.serializeObjectPretty(user);

        // 3. Serialization with nulls
        System.out.println("\n--- 3. Serialize with Nulls ---");
        User userWithNulls = new User(2, "bob", "[email protected]", null, true, null);
        String json3 = basicSerializer.serializeWithNulls(userWithNulls);
        System.out.println("With nulls: " + json3);

        // 4. Date formatting
        System.out.println("\n--- 4. Date Formatting ---");
        String json4 = basicSerializer.serializeWithDateFormat(user, "yyyy-MM-dd HH:mm:ss");
        System.out.println("Custom date format: " + json4);

        // 5. Complex object
        System.out.println("\n--- 5. Complex Object Serialization ---");
        List<Product> products = new java.util.ArrayList<>();
        products.add(new Product("P001", "Laptop", 999.99,
            new java.util.ArrayList<>(java.util.Arrays.asList("Electronics", "Computers")), true));
        products.add(new Product("P002", "Mouse", 29.99,
            new java.util.ArrayList<>(java.util.Arrays.asList("Electronics", "Accessories")), true));

        Order order = new Order(1001, user, products, 1029.98, "2025-12-28");
        String json5 = basicSerializer.serializeObjectPretty(order);
        System.out.println("Order:\n" + json5);

        // 6. Collections
        System.out.println("\n--- 6. Collection Serialization ---");
        CollectionSerializer collectionSerializer = new CollectionSerializer();

        List<User> users = new java.util.ArrayList<>();
        users.add(new User(1, "alice", "[email protected]", 25, true, new Date()));
        users.add(new User(2, "bob", "[email protected]", 30, true, new Date()));
        users.add(new User(3, "charlie", "[email protected]", 28, true, new Date()));

        String usersJson = collectionSerializer.serializeTypedList(users);
        System.out.println("Users list: " + usersJson);

        // 7. Field naming policy
        System.out.println("\n--- 7. Field Naming Policy ---");
        String json6 = basicSerializer.serializeWithFieldNaming(user);
        System.out.println("Lowercase with underscores: " + json6);

        // 8. Built-in JSONObject
        System.out.println("\n--- 8. Built-in JSONObject ---");
        BuiltInJsonSerializer builtInSerializer = new BuiltInJsonSerializer();
        String builtInJson = builtInSerializer.serializeWithBuiltIn(user);
        System.out.println("Built-in: " + builtInJson);

        System.out.println("\n=== All JSON Serialization Examples Completed ===");
    }
}

// Android Java JSON Deserialization Examples
// Using Gson library for parsing JSON

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.reflect.TypeToken;
import com.google.gson.JsonSyntaxException;
import org.json.JSONObject;
import org.json.JSONArray;
import org.json.JSONException;
import java.lang.reflect.Type;
import java.util.List;
import java.util.Map;

// Data model classes
class User {
    public int id;
    public String username;
    public String email;
    public Integer age;
    public boolean isActive;
    public String createdAt;

    public User() {}
}

class Product {
    public String productId;
    public String name;
    public double price;
    public List<String> tags;
    public boolean inStock;

    public Product() {}
}

class Order {
    public int orderId;
    public User user;
    public List<Product> products;
    public double totalAmount;
    public String orderDate;

    public Order() {}
}

// 1. Basic JSON Deserialization
class BasicJsonDeserializer {
    private Gson gson = new Gson();

    // Deserialize simple object
    public User deserializeUser(String json) {
        try {
            User user = gson.fromJson(json, User.class);
            System.out.println("Deserialized: " + user.username);
            return user;
        } catch (JsonSyntaxException e) {
            System.out.println("Parse error: " + e.getMessage());
            return null;
        }
    }

    // Deserialize with custom date format
    public User deserializeWithDateFormat(String json, String dateFormat) {
        Gson gsonWithFormat = new GsonBuilder()
            .setDateFormat(dateFormat)
            .create();

        return gsonWithFormat.fromJson(json, User.class);
    }

    // Deserialize to generic object
    public Object deserializeToObject(String json) {
        return gson.fromJson(json, Object.class);
    }
}

// 2. Collection Deserialization
class CollectionDeserializer {
    private Gson gson = new Gson();

    // Deserialize list
    public List<User> deserializeUserList(String json) {
        Type userListType = new TypeToken<List<User>>() {}.getType();
        return gson.fromJson(json, userListType);
    }

    // Deserialize map
    public Map<String, Object> deserializeToMap(String json) {
        Type mapType = new TypeToken<Map<String, Object>>() {}.getType();
        return gson.fromJson(json, mapType);
    }

    // Deserialize array of objects
    public User[] deserializeUserArray(String json) {
        return gson.fromJson(json, User[].class);
    }

    // Deserialize nested structures
    public Map<String, List<String>> deserializeNestedMap(String json) {
        Type nestedMapType = new TypeToken<Map<String, List<String>>>() {}.getType();
        return gson.fromJson(json, nestedMapType);
    }
}

// 3. Safe Deserialization
class SafeJsonDeserializer {
    private Gson gson = new Gson();

    // Safe parse with error handling
    public User safeDeserializeUser(String json) {
        try {
            return gson.fromJson(json, User.class);
        } catch (JsonSyntaxException e) {
            System.out.println("Deserialization error: " + e.getMessage());
            return null;
        }
    }

    // Parse with default value
    public User deserializeOrDefault(String json, User defaultValue) {
        try {
            return gson.fromJson(json, User.class);
        } catch (JsonSyntaxException e) {
            System.out.println("Using default value");
            return defaultValue;
        }
    }

    // Validate JSON structure
    public boolean isValidJson(String json) {
        try {
            gson.fromJson(json, Object.class);
            return true;
        } catch (JsonSyntaxException e) {
            return false;
        }
    }

    // Safe collection parsing
    public List<User> safeDeserializeList(String json) {
        try {
            Type userListType = new TypeToken<List<User>>() {}.getType();
            return gson.fromJson(json, userListType);
        } catch (JsonSyntaxException e) {
            System.out.println("List parse error: " + e.getMessage());
            return new java.util.ArrayList<>();
        }
    }
}

// 4. Deserialization with JSONObject
class JSONObjectDeserializer {

    // Parse User from JSONObject
    public User parseUser(JSONObject json) {
        User user = new User();
        try {
            user.id = json.getInt("id");
            user.username = json.getString("username");
            user.email = json.getString("email");
            user.age = json.optInt("age");
            user.isActive = json.optBoolean("isActive", true);
            user.createdAt = json.optString("createdAt", null);
        } catch (JSONException e) {
            System.out.println("Parse error: " + e.getMessage());
        }
        return user;
    }

    // Parse from JSON string
    public User parseFromString(String jsonString) {
        try {
            JSONObject json = new JSONObject(jsonString);
            return parseUser(json);
        } catch (JSONException e) {
            System.out.println("Parse error: " + e.getMessage());
            return null;
        }
    }

    // Parse list from JSONArray
    public List<User> parseUserList(JSONArray jsonArray) {
        List<User> users = new java.util.ArrayList<>();
        for (int i = 0; i < jsonArray.length(); i++) {
            try {
                JSONObject json = jsonArray.getJSONObject(i);
                users.add(parseUser(json));
            } catch (JSONException e) {
                System.out.println("Error parsing item " + i + ": " + e.getMessage());
            }
        }
        return users;
    }

    // Parse list from JSON array string
    public List<User> parseUserList(String jsonArrayString) {
        try {
            JSONArray jsonArray = new JSONArray(jsonArrayString);
            return parseUserList(jsonArray);
        } catch (JSONException e) {
            System.out.println("Array parse error: " + e.getMessage());
            return new java.util.ArrayList<>();
        }
    }

    // Parse with fallback values
    public User parseWithFallbacks(String jsonString) {
        try {
            JSONObject json = new JSONObject(jsonString);
            User user = new User();

            user.id = json.optInt("id", 0);
            user.username = json.optString("username", "unknown");
            user.email = json.optString("email", "");
            user.age = json.optInt("age", 0);
            user.isActive = json.optBoolean("isActive", true);

            return user;
        } catch (JSONException e) {
            System.out.println("Fallback parse error: " + e.getMessage());
            return new User();
        }
    }
}

// 5. Partial Deserialization
class PartialJsonDeserializer {

    // Extract specific fields
    public String extractField(String json, String fieldName) {
        try {
            JSONObject jsonObject = new JSONObject(json);
            if (jsonObject.has(fieldName)) {
                return jsonObject.getString(fieldName);
            }
            return null;
        } catch (JSONException e) {
            System.out.println("Extract error: " + e.getMessage());
            return null;
        }
    }

    // Extract multiple fields
    public Map<String, String> extractFields(String json, String[] fieldNames) {
        Map<String, String> result = new java.util.HashMap<>();
        try {
            JSONObject jsonObject = new JSONObject(json);
            for (String fieldName : fieldNames) {
                if (jsonObject.has(fieldName)) {
                    try {
                        result.put(fieldName, jsonObject.getString(fieldName));
                    } catch (JSONException e) {
                        result.put(fieldName, jsonObject.opt(fieldName));
                    }
                }
            }
        } catch (JSONException e) {
            System.out.println("Extract fields error: " + e.getMessage());
        }
        return result;
    }

    // Get JSON array at path
    public List<String> extractArrayAtPath(String json, String arrayField) {
        List<String> result = new java.util.ArrayList<>();
        try {
            JSONObject jsonObject = new JSONObject(json);
            if (jsonObject.has(arrayField)) {
                JSONArray jsonArray = jsonObject.getJSONArray(arrayField);
                for (int i = 0; i < jsonArray.length(); i++) {
                    result.add(jsonArray.getString(i));
                }
            }
        } catch (JSONException e) {
            System.out.println("Array extract error: " + e.getMessage());
        }
        return result;
    }
}

// 6. Streaming JSON Deserialization
class StreamingJsonDeserializer {

    // Parse using JsonReader (for large JSON files)
    public List<User> parseLargeJsonFile(String filePath) {
        List<User> users = new java.util.ArrayList<>();

        try {
            java.io.FileReader reader = new java.io.FileReader(filePath);
            com.google.gson.stream.JsonReader jsonReader = new com.google.gson.stream.JsonReader(reader);

            jsonReader.beginArray();
            while (jsonReader.hasNext()) {
                User user = new User();
                jsonReader.beginObject();

                while (jsonReader.hasNext()) {
                    String name = jsonReader.nextName();
                    switch (name) {
                        case "id":
                            user.id = jsonReader.nextInt();
                            break;
                        case "username":
                            user.username = jsonReader.nextString();
                            break;
                        case "email":
                            user.email = jsonReader.nextString();
                            break;
                        case "age":
                            user.age = jsonReader.nextInt();
                            break;
                        case "isActive":
                            user.isActive = jsonReader.nextBoolean();
                            break;
                        case "createdAt":
                            user.createdAt = jsonReader.nextString();
                            break;
                        default:
                            jsonReader.skipValue();
                    }
                }

                jsonReader.endObject();
                users.add(user);
            }
            jsonReader.endArray();

            jsonReader.close();
            reader.close();
        } catch (Exception e) {
            System.out.println("Streaming parse error: " + e.getMessage());
        }

        return users;
    }
}

// 7. Type Adapters
class CustomTypeAdapterDeserializer {

    // Deserialize with custom type adapter
    public static class DateDeserializer implements com.google.gson.JsonDeserializer<Date> {
        @Override
        public Date deserialize(com.google.gson.JsonElement json, Type typeOfT,
                                com.google.gson.JsonDeserializationContext context) {
            try {
                String dateStr = json.getAsString();
                java.text.SimpleDateFormat formatter = new java.text.SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss");
                return formatter.parse(dateStr);
            } catch (Exception e) {
                return null;
            }
        }
    }

    // Register and deserialize with custom adapter
    public User deserializeWithCustomAdapter(String json) {
        Gson gson = new GsonBuilder()
            .registerTypeAdapter(Date.class, new DateDeserializer())
            .create();

        return gson.fromJson(json, User.class);
    }
}

// Main demonstration
class JsonDeserializationDemo {
    public static void demonstrateJsonDeserialization() {
        System.out.println("=== Android Java JSON Deserialization Examples ===\n");

        // 1. Basic deserialization
        System.out.println("--- 1. Basic Deserialization ---");
        BasicJsonDeserializer deserializer = new BasicJsonDeserializer();

        String userJson = '{"id":1,"username":"alice","email":"[email protected]","age":25,"isActive":true}';
        User user = deserializer.deserializeUser(userJson);
        System.out.println("User: " + user.username + ", " + user.email);

        // 2. Collection deserialization
        System.out.println("\n--- 2. Collection Deserialization ---");
        CollectionDeserializer collectionDeserializer = new CollectionDeserializer();

        String usersJson = "[{" +
            "\"id\":1,\"username\":\"alice\",\"email\":\"[email protected]\"}," +
            "{" +
            "\"id\":2,\"username\":\"bob\",\"email\":\"[email protected]\"}" +
            "]";

        List<User> users = collectionDeserializer.deserializeUserList(usersJson);
        System.out.println("Users count: " + users.size());

        // 3. Safe deserialization
        System.out.println("\n--- 3. Safe Deserialization ---");
        SafeJsonDeserializer safeDeserializer = new SafeJsonDeserializer();

        String invalidJson = "{invalid json}";
        User parsedUser = safeDeserializer.safeDeserializeUser(invalidJson);
        System.out.println("Parsed with error handling: " + (parsedUser != null ? parsedUser.username : "null"));

        boolean isValid = safeDeserializer.isValidJson(userJson);
        System.out.println("Is valid: " + isValid);

        // 4. JSONObject deserialization
        System.out.println("\n--- 4. JSONObject Deserialization ---");
        JSONObjectDeserializer jsonObjectDeserializer = new JSONObjectDeserializer();

        User userFromObj = jsonObjectDeserializer.parseFromString(userJson);
        System.out.println("Parsed from JSONObject: " + userFromObj.username);

        // 5. Partial deserialization
        System.out.println("\n--- 5. Partial Deserialization ---");
        PartialJsonDeserializer partialDeserializer = new PartialJsonDeserializer();

        String username = partialDeserializer.extractField(userJson, "username");
        System.out.println("Extracted username: " + username);

        String[] fields = {"username", "email", "age"};
        Map<String, String> extracted = partialDeserializer.extractFields(userJson, fields);
        System.out.println("Extracted fields: " + extracted);

        // 6. Complex nested object
        System.out.println("\n--- 6. Complex Nested Object ---");
        String orderJson = "{" +
            "\"orderId\": 1001," +
            "\"user\": " + userJson + "," +
            "\"totalAmount\": 1029.98," +
            "\"orderDate\": \"2025-12-28\"" +
            "}";

        Order order = new Gson().fromJson(orderJson, Order.class);
        System.out.println("Order ID: " + order.orderId);
        System.out.println("User: " + (order.user != null ? order.user.username : "null"));

        System.out.println("\n=== All JSON Deserialization Examples Completed ===");
    }
}