之前公司里写项目，前台需要用到ajax请求json数据
但是后台方面禁止添加额外的jar，所以没办法只能自己写一个工具类
还好是生成json而不是解析json，用递归实现起来应该不难
类型转换的坑
Integer[] => Object => Object[]的转换过程是没有问题
但是int[] => Object => Object[]会出错，基本上所有的基本类型的数组这转换都会出问题
解决方法是重新构建Object[]，把每一项通过反射拿到再放进去
还要注意[][]…多维数组的生成
public static Object[] fmtArrayToObjectArray(Object obj) {
int length = Array.getLength(obj);
Object[] o = new Object[length];
for (int i = 0; i < o.length; i++) {
if (Array.get(obj, i) == null) {
o[i] = null;
} else if (Array.get(obj, i).getClass().isArray()) {
//多维数组
o[i] = fmtArrayToObjectArray(Array.get(obj, i));
} else {
o[i] = Array.get(obj, i);
}
}
return o;
}
反射获取属性的坑
要获取定义了get方法的属性，但是要注意到有些是通过继承获得的
/**
* 获取一个类自身和继承获得的所有Field
*
* @param obj
* @return
*/
private static List<Field> listAllField(Object obj) {
List<Field> resultList = new ArrayList<Field>();
Class<?> clazz = obj.getClass();
while (clazz != null) {
for (Field field : clazz.getDeclaredFields()) {
resultList.add(field);
}
clazz = clazz.getSuperclass();
}
return resultList;
}
/**
* 通过反射执行对象的get方法
*
* @param name
* @param obj
* @return
*/
private static Object invokeGet(String name, Object obj) {
String methodName = "get" + name.substring(0, 1).toUpperCase() + name.substring(1);
Class<?> clazz = obj.getClass();
Object result = null;
try {
result = clazz.getMethod(methodName).invoke(obj);
} catch (Exception e) {
result = null;
}
return result;
}
转换的代码
public static String jsonGenerater(Object value) {
// 不处理null
boolean ignoreNullValue = true;
// 日期的格式
String datePattern = "yyyy/MM/dd HH:mm:ss";
// null
if (value == null) {
if (ignoreNullValue) {
return "";
}
return "null";
}
// 数值,布尔
if (value instanceof Byte || value instanceof Integer || value instanceof Float || value instanceof Long || value instanceof Boolean) {
return String.valueOf(value);
}
// 字符串
if (value instanceof String) {
String v = (String) value;
// 注意转义问题
return "\"" + v.replace("\n", "\\n").replace("\"", "\\\"") + "\"";
}
// 日期
if (value instanceof Date) {
SimpleDateFormat sdf = new SimpleDateFormat(datePattern);
String result = null;
try {
result = sdf.format(value);
} catch (Exception e) {
result = jsonGenerater(e.getMessage());
}
return jsonGenerater(result);
}
// 数组
if (value.getClass().isArray()) {
StringBuilder sb = new StringBuilder("[");
Object[] arr = fmtArrayToObjectArray(value);
for (int i = 0; i < arr.length; i++) {
sb.append(jsonGenerater(arr[i]) + ",");
}
if (sb.charAt(sb.length() - 1) == ',') {
sb.deleteCharAt(sb.length() - 1);
}
sb.append("]");
return sb.toString();
}
// 列表
if (value instanceof List) {
StringBuilder sb = new StringBuilder("[");
List<?> list = (List<?>) value;
for (int i = 0; i < list.size(); i++) {
sb.append(jsonGenerater(list.get(i)) + ",");
}
if (sb.charAt(sb.length() - 1) == ',') {
sb.deleteCharAt(sb.length() - 1);
}
sb.append("]");
return sb.toString();
}
// 字典
if (value instanceof Map) {
StringBuilder sb = new StringBuilder("{");
Map<?, ?> map = (Map<?, ?>) value;
Iterator<?> entries = map.entrySet().iterator();
while (entries.hasNext()) {
Map.Entry<?, ?> entry = (Entry<?, ?>) entries.next();
if (ignoreNullValue && entry.getValue() == null) {
continue;
}
sb.append("\"" + entry.getKey().toString() + "\":" + jsonGenerater(entry.getValue()) + ",");
}
if (sb.charAt(sb.length() - 1) == ',') {
sb.deleteCharAt(sb.length() - 1);
}
sb.append("}");
return sb.toString();
}
// 在此之前添加其他类型的处理规则
// 到这里基本就是自定义类型了
StringBuilder sb = new StringBuilder("{");
List<Field> list = listAllField(value);
for (int i = 0; i < list.size(); i++) {
String fName = list.get(i).getName();
Object rflectValue = invokeGet(fName, value);
if (ignoreNullValue && rflectValue == null) {
continue;
}
sb.append("\"" + fName + "\":" + jsonGenerater(rflectValue) + ",");
}
if (sb.charAt(sb.length() - 1) == ',') {
sb.deleteCharAt(sb.length() - 1);
}
sb.append("}");
return sb.toString();
}
测试
public static void main(String[] args) throws Exception {
Map<String, Object> map = new HashMap<String, Object>();
map.put("date", new Date());
map.put("string", "123 abc \" 123\n789");
int[][] arr = { { 1, 2 }, { 3, 4 } };
map.put("arr", arr);
map.put("null", null);
User u = new User();
u.setAge(18);
u.setName("张三");
map.put("user", u);
try {
System.out.println(jsonGenerater(map));
} catch (Exception e) {
System.out.println("{\"error\":" + jsonGenerater(e.toString()) + "}");
}
}
输出
没毛病
{"date":"2018/03/04 16:00:17","arr":[[1,2],[3,4]],"string":"123 abc \" 123\n789","user":{"name":"张三","age":18}}