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  1. /* package whatever; // don't place package name! */
  2.  
  3. import java.io.IOException;
  4. import java.lang.reflect.Constructor;
  5. import java.lang.reflect.Field;
  6. import java.lang.reflect.InvocationTargetException;
  7. import java.lang.reflect.Method;
  8. import java.util.HashMap;
  9. import java.util.Map;
  10.  
  11. class Ideone {
  12.   public static void main(String[] args) throws IOException {
  13.     String json = "{\"id\":1, \"name\":\"jsmith\"}";
  14.     NaiveObjectMapper objectMapper = new NaiveObjectMapper();
  15.     User user = objectMapper.readValue(json, User.class);
  16.     System.out.println(user);
  17.   }
  18.  
  19.   public static class NaiveObjectMapper {
  20.     private Map<String, Object> fieldsAndMethods;
  21.     private NaiveJsonParser parser;
  22.  
  23.     public <T> T readValue(String content, Class<T> valueType) {
  24.       parser = new NaiveJsonParser(content);
  25.  
  26.       try {
  27.         // aggregate all value type fields and methods inside a map
  28.         fieldsAndMethods = new HashMap<>();
  29.         for (Field field : valueType.getDeclaredFields()) {
  30.           fieldsAndMethods.put(field.getName(), field);
  31.         }
  32.         for (Method method : valueType.getMethods()) {
  33.           fieldsAndMethods.put(method.getName(), method);
  34.         }
  35.  
  36.         // create an instance of value type by calling its default constructor
  37.         Constructor<T> constructor = valueType.getConstructor();
  38.         Object bean = constructor.newInstance(new Object[0]);
  39.  
  40.         // loop through all json nodes
  41.         String propName;
  42.         while ((propName = parser.nextFieldName()) != null) {
  43.           // find the corresponding field
  44.           Field prop = (Field) fieldsAndMethods.get(propName);
  45.           // get and set field value
  46.           deserializeAndSet(prop, bean);
  47.         }
  48.         return (T) bean;
  49.       } catch (NoSuchMethodException e) {
  50.         e.printStackTrace();
  51.       } catch (IllegalAccessException e) {
  52.         e.printStackTrace();
  53.       } catch (InstantiationException e) {
  54.         e.printStackTrace();
  55.       } catch (InvocationTargetException e) {
  56.         e.printStackTrace();
  57.       }
  58.  
  59.       return null;
  60.     }
  61.  
  62.     private void deserializeAndSet(Field prop, Object bean) {
  63.       Class<?> propType = prop.getType();
  64.       Method setter = (Method) fieldsAndMethods.get(getFieldSetterName(prop));
  65.       try {
  66.         if (propType.isPrimitive()) {
  67.           if (propType.getName().equals("int")) {
  68.             setter.invoke(bean, parser.getIntValue());
  69.           }
  70.         } else if (propType == String.class) {
  71.           setter.invoke(bean, parser.getTextValue());
  72.         }
  73.       } catch (IllegalAccessException e) {
  74.         e.printStackTrace();
  75.       } catch (InvocationTargetException e) {
  76.         e.printStackTrace();
  77.       }
  78.     }
  79.  
  80.     private String getFieldSetterName(Field prop) {
  81.       String propName = prop.getName();
  82.       return "set" + propName.substring(0, 1).toUpperCase() + propName.substring(1);
  83.     }
  84.   }
  85.  
  86.   static class NaiveJsonParser {
  87.     String[] nodes;
  88.     int currentNodeIdx = -1;
  89.     String currentProperty;
  90.     String currentValueStr;
  91.  
  92.     public NaiveJsonParser(String content) {
  93.       // split the content into 'property:value' nodes
  94.       nodes = content.replaceAll("[{}]", "").split(",");
  95.     }
  96.  
  97.     public String nextFieldName() {
  98.       if ((++currentNodeIdx) >= nodes.length) {
  99.         return null;
  100.       }
  101.       String[] propertyAndValue = nodes[currentNodeIdx].split(":");
  102.       currentProperty = propertyAndValue[0].replace("\"", "").trim();
  103.       currentValueStr = propertyAndValue[1].replace("\"", "").trim();
  104.       return currentProperty;
  105.     }
  106.  
  107.     public String getTextValue() {
  108.       return String.valueOf(currentValueStr);
  109.     }
  110.  
  111.     public int getIntValue() {
  112.       return Integer.valueOf(currentValueStr).intValue();
  113.     }
  114.   }
  115.  
  116.   public static class User {
  117.     private int id;
  118.     private String name;
  119.  
  120.     public int getId() {
  121.       return id;
  122.     }
  123.  
  124.     public void setId(int id) {
  125.       this.id = id;
  126.     }
  127.  
  128.     public String getName() {
  129.       return name;
  130.     }
  131.  
  132.     public void setName(String name) {
  133.       this.name = name;
  134.     }
  135.  
  136.     @Override
  137.     public String toString() {
  138.       return "id = " + id + ", name = \"" + name + "\"";
  139.     }
  140.   }
  141. }
  142.  
Success #stdin #stdout 0.05s 4386816KB
comments (?)
stdin 
Standard input is empty
stdout 
id = 1, name = "jsmith"
https://ideone.com/v3ZuUZ
language:
Java (HotSpot 12)
created:
8 years ago
visibility:
public

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