Java 反射（二）：应用示例

1. 写一个利用反射实现简单的通用序列化/反序列化的类 SimpleMap，其提供两个静态方法：public static String toString(Object obj)/public static Object fromString(String str)

• toString() 方法：将对象 obj 转换为字符串

  public static String toString(Object obj) {
      try {
          Class<?> cls = obj.getClass();
          StringBuilder sb = new StringBuilder();
          sb.append(cls.getName() + "\n");
          for(Field f : cls.getDeclaredFields()) {
              if(!f.isAccessible()) {
                  f.setAccessible(true);
              }
              sb.append(f.getName() + "=" + f.get(obj).toString() + "\n");
          }
          return sb.toString();
      } catch(IllegalAccessException e) {
          throw new RuntimeException;
      }
  }

• fromString() 方法：将字符串转换为对象

  public static Object fromString(String str) {
      try {
          String[] lines = str.split("\n");
          if(lines.length < 1) {
              throw new IllegalArgumentException(str);
          }
          Class<?> cls = Class.forName(lines[0]);
          Object obj = cls.newInstance();
          if(lines.length > 1) {
              for(int i = 1; i<lines.length:i++) {
                  String[] fv = lines[i].split("=");
                  if(fv.length != 2) {
                      throw new IllegalArgumentException(lines[i]);
                  }
                  Field f = cls.getDeclaredField(fv[0]);
                  if(!f.isAccessible()) {
                      f.setAccessible(true);
                  }
                  setFieldValue(f, obj, fv[1]);
              }
          }
          return obj;
      } catch(Exception e) {
          throw new RuntimeException(e);
      }
  }

• setFieldValue() 方法

  private static void setFieldValue(Field f, Object obj, String value) throws Exception {
      Class<?> type = f.getType();
      if(type == int.class) {
          f.setInt(obj, Integer.parseInt(value));
      } else if(type == byte.class) {
          f.setByte(obj, Byte.parseByte(value));
      } else if(type == short.class) {
          f.setShort(obj, Short.parseShort(value));
      } else if(type == long.class) {
          f.setLong(obj, Long.parseLong(value));
      } else if(type == float.class) {
          f.setFloat(obj, Float.parseFloat(value));
      } else if(type == double.class) {
          f.setDouble(obj, Double.parseDouble(value));
      } else if(type == char.class) {
          f.setChar(obj, value.charAt(0));
      } else if(type == boolean.class) {
          f.setBoolean(obj, Boolean.parseBoolean(value));
      } else if(type == String.class) {
          f.set(obj, value);
      } else {
          Constructor<?> ctor = type.getConstructor(new Class[] { String.class });
          f.set(obj, ctor.newInstance(value));
      }
  }