Json libraries. Complete home task

src/com/company/json/Ignore.java

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+package com.company.json;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+/**
+ * Mark its annotated field to be ignored during serialization or other operation that needs access to the field.
+ */
+@Target(ElementType.FIELD)
+@Retention(RetentionPolicy.RUNTIME)
+public @interface Ignore {
+
+}

src/com/company/json/JsonSerializer.java

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+package com.company.json;
+
+import com.company.json.adapters.JsonDataAdapter;
+import com.company.json.adapters.UseDataAdapter;
+import org.json.JSONArray;
+import org.json.JSONException;
+import org.json.JSONObject;
+
+import java.lang.reflect.Field;
+import java.util.Arrays;
+import java.util.HashSet;
+import java.util.Set;
+
+
+/**
+ * JsonSerializer converts Java objects to JSON representation.
+ *
+ */
+public class JsonSerializer {
+
+    /**
+     * simpleTypes contains java classes for which we should not make any deeper serialization and we should return object as is
+     * and use toString() method to get it serialized representation
+     */
+    private static Set<Class> simpleTypes = new HashSet<Class>(Arrays.asList(
+            JSONObject.class,
+            JSONArray.class,
+            String.class,
+            Integer.class,
+            Short.class,
+            Long.class,
+            Byte.class,
+            Double.class,
+            Float.class,
+            Character.class,
+            Boolean.class,
+            int.class,
+            short.class,
+            long.class,
+            byte.class,
+            double.class,
+            float.class,
+            char.class,
+            boolean.class
+    ));
+
+    /**
+     * Main method to convert Java object to JSON. If type of the object is part of the simpleTypes object itself will be returned.
+     * If object is null String value "null" will be returned.
+     * @param o object to serialize.
+     * @return JSON representation of the object.
+     */
+    public static Object serialize(Object o) {
+        if (null == o) {
+            return "null";
+        }
+        if (simpleTypes.contains(o.getClass())) {
+            return o;
+        } else {
+            try {
+                return toJsonObject(o);
+            } catch (Exception e) {
+                e.printStackTrace();
+                return null;
+            }
+        }
+    }
+
+    /**
+     * Converts Java object to JSON. Uses reflection to access object fields.
+     * Uses JsonDataAdapter to serialize complex values. Ignores @Ignore annotated fields.
+     * @param o object to serialize to JSON
+     * @return JSON object.
+     * @throws IllegalAccessException
+     * @throws InstantiationException
+     */
+    private static JSONObject toJsonObject(Object o) throws Exception {
+        //implement me
+        Class<?> clases = o.getClass();
+        Field [] fields = clases.getDeclaredFields();
+        JSONObject jsonObject = new JSONObject();
+        for (Field field : fields) {
+            try {
+                field.setAccessible(true);
+                if (!field.isAnnotationPresent(Ignore.class)) {
+                    if (!field.isAnnotationPresent(UseDataAdapter.class)) {
+                        jsonObject.put(field.getName(), field.get(o));
+                    } else {
+                        UseDataAdapter annotation = field.getAnnotation(UseDataAdapter.class);
+                        Class annotationClass = annotation.value();
+                        JsonDataAdapter dataAdapter = (JsonDataAdapter) annotationClass.newInstance();
+                        jsonObject.put(field.getName(), dataAdapter.toJson(field.get(o)));
+                    }
+                }
+            } catch (JSONException e) {
+                e.printStackTrace();
+            }
+        }
+        return jsonObject;
+    }
+}

src/com/company/json/adapters/CollectionAdapter.java

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+package com.company.json.adapters;
+
+import com.company.json.JsonSerializer;
+import org.json.JSONArray;
+import org.json.JSONException;
+
+import java.util.Collection;
+
+/**
+ * Converts all objects that extends java.util.Collections to JSONArray.
+ */
+public class CollectionAdapter implements com.company.json.adapters.JsonDataAdapter<Collection> {
+    @Override
+    public Object toJson(Collection c) throws JSONException{
+        //implement me
+        JSONArray jsonArray = new JSONArray();
+        c.stream().forEach(object -> jsonArray.put(JsonSerializer.serialize (object)));
+        return jsonArray;
+    }
+}

src/com/company/json/adapters/ColorAdapter.java

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+package com.company.json.adapters;
+
+import java.awt.Color;
+
+/**
+ * Converts object of type java.awt.Color to its String representation. i.e. Color.GRAY = "(128,128,128)"
+ */
+public class ColorAdapter implements JsonDataAdapter<Color> {
+    @Override
+    public Object toJson(Color o) {
+        return "(" + o.getRed() + "," + o.getGreen() + "," + o.getBlue() + ")";
+    }
+}

src/com/company/json/adapters/DateAdapter.java

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+package com.company.json.adapters;
+
+import sun.util.calendar.BaseCalendar;
+
+import java.text.DateFormat;
+import java.text.SimpleDateFormat;
+import java.util.Date;
+
+/**
+ * Converts object of type java.util.Date to String by using dd/MM/yyyy format
+ */
+public class DateAdapter implements JsonDataAdapter<Date> {
+    @Override
+    public Object toJson(Date date) {
+        //implement me
+        DateFormat newFormat = new SimpleDateFormat();
+        String formated = newFormat.format(date);
+        return formated;
+    }
+}

src/com/company/json/adapters/JsonDataAdapter.java

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+package com.company.json.adapters;
+
+import org.json.JSONException;
+
+/**
+ * JsonDataAdapter contains instructions how to serialize Java object to Json representation.
+ * @param <T> determines type adapter works with.
+ */
+public interface JsonDataAdapter<T> {
+    Object toJson(T o) throws JSONException;
+}

src/com/company/json/adapters/MapAdapter.java

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+package com.company.json.adapters;
+
+import com.company.json.JsonSerializer;
+import org.json.JSONException;
+import org.json.JSONObject;
+
+import java.util.Map;
+
+/**
+ * Converts all objects that extends java.util.Map to JSONObject.
+ */
+
+public class MapAdapter implements JsonDataAdapter<Map> {
+    @Override
+    public Object toJson(Map map) throws JSONException {
+        JSONObject m = new JSONObject();
+        for (Object key : map.keySet()) {
+            m.put(key.toString(), JsonSerializer.serialize(map.get(key)));
+        }
+        return m;
+    }
+}

src/com/company/json/adapters/UseDataAdapter.java

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+package com.company.json.adapters;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+/**
+ * Determines class of JsonDataAdapter that should be used to serialize annotated field value.
+ */
+@Target(ElementType.FIELD)
+@Retention(RetentionPolicy.RUNTIME)
+public @interface UseDataAdapter {
+    Class<? extends JsonDataAdapter> value();
+}

src/com/company/test/Cat.java

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+package com.company.test;
+
+import com.company.json.adapters.*;
+
+import java.awt.*;
+import java.util.*;
+import java.util.List;
+
+/**
+ * Simple Cat that will be used for testing JSON serialization.
+ */
+public class Cat {
+    private int age;
+    private String name;
+    private Cat myself;
+
+    private Date birthDate;
+
+    @UseDataAdapter(ColorAdapter.class)
+    private Color color;
+
+    private List<Integer> whiskers = new ArrayList<>();
+
+    @UseDataAdapter(MapAdapter.class)
+    private Map<String, com.company.test.Paw> paws = new HashMap<>();
+
+    public Cat() {
+        myself = this;
+    }
+
+    public int getAge() {
+        return age;
+    }
+
+    public void setAge(int age) {
+        this.age = age;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public Date getBirthDate() {
+        return birthDate;
+    }
+
+    public void setBirthDate(Date birthDate) {
+        this.birthDate = birthDate;
+    }
+
+    public Color getColor() {
+        return color;
+    }
+
+    public void setColor(Color color) {
+        this.color = color;
+    }
+
+    public Map<String, com.company.test.Paw> getPaws() {
+        return paws;
+    }
+
+    public void setPaws(Map<String, com.company.test.Paw> paws) {
+        this.paws = paws;
+    }
+
+    public List<Integer> getWhiskers() {
+        return whiskers;
+    }
+
+    public void setWhiskers(List<Integer> whiskers) {
+        this.whiskers = whiskers;
+    }
+
+    public Cat getMyself() {
+        return myself;
+    }
+
+    public void setMyself(Cat myself) {
+        this.myself = myself;
+    }
+}

src/com/company/test/Paw.java

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+package com.company.test;
+
+import java.awt.*;
+
+public class Paw {
+    private Integer length;
+
+    private Color color;
+
+    public Paw(Integer length, Color color) {
+        this.length = length;
+        this.color = color;
+    }
+
+    public Integer getLength() {
+        return length;
+    }
+
+    public void setLength(Integer length) {
+        this.length = length;
+    }
+
+    public Color getColor() {
+        return color;
+    }
+
+    public void setColor(Color color) {
+        this.color = color;
+    }
+}

src/com/company/test/Test.java

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+package com.company.test;
+
+import com.company.json.JsonSerializer;
+
+import java.awt.*;
+import java.util.*;
+import java.util.List;
+
+public class Test {
+    public static void main(String[] args) throws IllegalAccessException {
+        Cat cat = new Cat();
+        cat.setColor(Color.GRAY);
+        cat.setAge(4);
+        cat.setName("Tom");
+
+        List<Integer> whiskers = cat.getWhiskers();
+        whiskers.add(1);
+        whiskers.add(2);
+        whiskers.add(3);
+        whiskers.add(4);
+        whiskers.add(5);
+        whiskers.add(6);
+
+        cat.setBirthDate(new Date());
+        cat.getPaws().put("front-left", new Paw(23, Color.GRAY));
+        cat.getPaws().put("front-right", new Paw(24, Color.WHITE));
+        cat.getPaws().put("back-left", new Paw(23, Color.BLACK));
+        cat.getPaws().put("back-right", new Paw(22, Color.GRAY));
+
+        System.out.println(JsonSerializer.serialize(cat));
+    }
+}