自实现JAVA对象转为json字符串

所属分类：[JAVA] | 创建时间：2014-11-26 | 文章属性：原创 | 文章来源：http://windfly.cn | 作者：windfly

##功能
>自定义按需实现由java对象转换成json字符串

##自定义
>1. 只要有get或is方法即视为可输出，如getName()，则输出 "name":xxx  , isAdmin()，则输出 "admin":true
>1. 返回值为数字类型的，无双引号，返回值为null的不输出，返回值为日期类型的则输出格式为 2014-11-11 11:11:11
>1. 父类有get方法的也会被输出

##实现代码
```
public static String toJson(Object obj) {
		if (obj == null) {
			return null;
		}
		if (obj instanceof String) {
			return "\"" + obj.toString() + "\"";
		}

if (obj instanceof Map) {
			@SuppressWarnings({ "rawtypes", "unchecked" })
			Set<Map.Entry> entrySet = ((Map) obj).entrySet();
			StringBuilder sb = new StringBuilder("{");
			for (@SuppressWarnings("rawtypes")
			Map.Entry entry : entrySet) {
				sb.append("\"").append(entry.getKey()).append("\"").append(":")
						.append(toJson(entry.getValue())).append(",");
			}
			if (sb.length() > 0) {
				sb.setLength(sb.length() - 1);
			}
			sb.append("}");
			return sb.toString();
		}

if (obj instanceof Number || obj instanceof Boolean) {
			return String.valueOf(obj);
		}

if (obj instanceof Collection) {
			StringBuilder sb = new StringBuilder("[");
			for (Object eo : (Collection<?>) obj) {
				sb.append(toJson(eo)).append(",");
			}
			if (sb.length() > 0) {
				sb.setLength(sb.length() - 1);
			}
			sb.append("]");
			return sb.toString();
		}

if (obj instanceof Date || obj instanceof java.sql.Date
				|| obj instanceof Calendar) {
			return "\""
					+ new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(obj)
					+ "\"";
		}

// object
		Class<? extends Object> cls = obj.getClass();
		if (cls.isPrimitive()) {
			return cls.toString();
		}
		if (cls.isAnnotation()) {
			return "";
		}
		if (cls.isArray()) {
			StringBuilder sb = new StringBuilder("[");
			int length = Array.getLength(obj);
			for (int i = 0; i < length; i++) {
				sb.append(toJson(Array.get(obj, i))).append(",");
			}
			if (sb.length() > 0) {
				sb.setLength(sb.length() - 1);
			}
			sb.append("]");
			return sb.toString();
		}

if (cls.isEnum()) {
			return "";
		}
		if (cls.isInterface()) {
			return "";
		}
		if (cls.isSynthetic()) {
			return "";
		}

StringBuilder sb = new StringBuilder();
		sb.append("{");

BeanInfo beanInfo;
		try {
			beanInfo = Introspector.getBeanInfo(obj.getClass(), Object.class);
			PropertyDescriptor[] propertyDescriptors = beanInfo
					.getPropertyDescriptors();
			for (PropertyDescriptor propertyDescriptor : propertyDescriptors) {
				Method readMethod = propertyDescriptor.getReadMethod();
				if (readMethod == null) {
					continue;
				}
				Object value = null;
				try {
					value = readMethod.invoke(obj);
				} catch (IllegalAccessException e) {
					logger.log(Level.FINE, e.getMessage(), e);
				} catch (IllegalArgumentException e) {
					logger.log(Level.FINE, e.getMessage(), e);
				} catch (InvocationTargetException e) {
					logger.log(Level.FINE, e.getMessage(), e);
				}
				if (value == null) {
					continue;
				}
				sb.append("\"").append(propertyDescriptor.getName())
						.append("\"").append(":");
				sb.append(toJson(value));
				sb.append(",");
			}
		} catch (IntrospectionException e) {
			throw new RuntimeException(e);
		}

if (sb.length() > 1) {
			sb.setLength(sb.length() - 1);
		}
		sb.append("}");
		return sb.toString();
	}
```