Java中把一个对象转换成JsonString

**
 * Object To json String
 * 
 * @param obj
 * 
 * @return json String
 */
public static String objToJsonString(Object obj) {
     
    // 初始化返回值
    String json = "str_empty";
 
    if (obj == null) {
        return json;
    }
 
    StringBuilder buff = new StringBuilder();
    Field fields[] = obj.getClass().getFields();
    try {
        buff.append("[");
        buff.append("{");
        int i = 0;
        for (Field field : fields) {
            if (i != 0) {
                buff.append(",");
            }
            buff.append(field.getName());
            buff.append(":");
            buff.append("\"");
            buff.append(field.get(obj) == null ? "" : field.get(obj));
            buff.append("\"");
            i++;
        }
        buff.append("}");
        buff.append("]");
        json = buff.toString();
    } catch (Exception e) {
        throw new RuntimeException("cause:" + e.toString());
    }
    return json;
}