java对象怎么与JSON互相转换

import java.beans.IntrospectionException;import java.beans.Introspector;import java.beans.PropertyDescriptor;import java.util.ArrayList;import java.util.HashMap;import java.util.Iterator;import java.util.List;import java.util.Map;import java.util.Set;import org.json.JSONObject;public class JsonUtils {  private static String beanToJson(Object bean) {  StringBuilder json = new StringBuilder();  json.append("{");  PropertyDescriptor[] props = null;  try {   props = Introspector.getBeanInfo(bean.getClass(), Object.class)     .getPropertyDescriptors();  } catch (IntrospectionException e) {  }  if (props != null) {   for (int i = 0; i < props.length; i++) {    try {     String name = objToJson(props[i].getName());     String value = objToJson(props[i].getReadMethod()       .invoke(bean));     json.append(name);     json.append(":");     json.append(value);     json.append(",");    } catch (Exception e) {    }   }   json.setCharAt(json.length() - 1, '}');  } else {   json.append("}");  }  return json.toString(); }  private static String listToJson(List<&#63;> list) {  StringBuilder json = new StringBuilder();  json.append("[");  if (list != null && list.size() > 0) {   for (Object obj : list) {    json.append(objToJson(obj));    json.append(",");   }   json.setCharAt(json.length() - 1, ']');  } else {   json.append("]");  }  return json.toString(); }  private static String arrayToJson(Object[] array) {  StringBuilder json = new StringBuilder();  json.append("[");  if (array != null && array.length > 0) {   for (Object obj : array) {    json.append(objToJson(obj));    json.append(",");   }   json.setCharAt(json.length() - 1, ']');  } else {   json.append("]");  }  return json.toString(); }  private static String mapToJson(Map<&#63;, &#63;> map) {  StringBuilder json = new StringBuilder();  json.append("{");  if (map != null && map.size() > 0) {   for (Object key : map.keySet()) {    json.append(objToJson(key));    json.append(":");    json.append(objToJson(map.get(key)));    json.append(",");   }   json.setCharAt(json.length() - 1, '}');  } else {   json.append("}");  }  return json.toString(); }  private static String setToJson(Set<&#63;> set) {  StringBuilder json = new StringBuilder();  json.append("[");  if (set != null && set.size() > 0) {   for (Object obj : set) {    json.append(objToJson(obj));    json.append(",");   }   json.setCharAt(json.length() - 1, ']');  } else {   json.append("]");  }  return json.toString(); } private static String stringToJson(String s) {  if (s == null) {   return "";  }  StringBuilder sb = new StringBuilder();  for (int i = 0; i < s.length(); i++) {   char ch = s.charAt(i);   switch (ch) {   case '"':    sb.append("\\\"");    break;   case '\\':    sb.append("\\\\");    break;   case '\b':    sb.append("\\b");    break;   case '\f':    sb.append("\\f");    break;   case '\n':    sb.append("\\n");    break;   case '\r':    sb.append("\\r");    break;   case '\t':    sb.append("\\t");    break;   case '/':    sb.append("\\/");    break;   default:    if (ch >= '\u0000' && ch <= '\u001F') {     String ss = Integer.toHexString(ch);     sb.append("\\u");     for (int k = 0; k < 4 - ss.length(); k++) {      sb.append('0');     }     sb.append(ss.toUpperCase());    } else {     sb.append(ch);    }   }  }  return sb.toString(); } public static String objToJson(Object obj) {  StringBuilder json = new StringBuilder();  if (obj == null) {   json.append("\"\"");  } else if (obj instanceof Number) {   Number num = (Number)obj;   json.append(num.toString());  } else if (obj instanceof Boolean) {   Boolean bl = (Boolean)obj;   json.append(bl.toString());  } else if (obj instanceof String) {   json.append("\"").append(stringToJson(obj.toString())).append("\"");  } else if (obj instanceof Object[]) {   json.append(arrayToJson((Object[]) obj));  } else if (obj instanceof List) {   json.append(listToJson((List) obj));  } else if (obj instanceof Map) {   json.append(mapToJson((Map) obj));  } else if (obj instanceof Set) {   json.append(setToJson((Set) obj));  } else {   json.append(beanToJson(obj));  }  return json.toString(); }   @SuppressWarnings("unchecked") public static Map<String, Object> json2Map(String jsonString) {    Map<String, Object> map = new HashMap<String, Object>();  try {   if(null != jsonString && !"".equals(jsonString)){    JSONObject jsonObject = new JSONObject(jsonString);       Iterator keyIter = jsonObject.keys();    String key = "";    Object value = null;       while (keyIter.hasNext()) {     key = (String) keyIter.next();     value = jsonObject.get(key);     map.put(key, value);    }   }  } catch (Exception e) {   e.printStackTrace();  }  return map; }  //测试方法 public static void main(String[] args) {  Map<String,Object> params = new HashMap<String,Object>();  params.put("callId123", Integer.valueOf(1000));  Map retMap = new HashMap();  retMap.put("params", params);  retMap.put("result", true);  List ls = new ArrayList();  ls.add(new HashMap());  ls.add("hello world!!");  ls.add(new String[4]);  retMap.put("list", ls);    String[] strArray = new String[10];  strArray[1]="first";  strArray[2]="2";  strArray[3]="3";  System.out.println("Boolean:"+JsonUtils.objToJson(true));  System.out.println("Number:"+JsonUtils.objToJson(23.3));  System.out.println("String:"+JsonUtils.objToJson("sdhfsjdgksdlkjfk\"sd,!#%$^&*#(*@&*%&*$fsdfsdfsdf"));  System.out.println("Map :"+JsonUtils.objToJson(retMap));  System.out.println("List:"+JsonUtils.objToJson(ls));  System.out.println("Array:"+JsonUtils.objToJson(strArray));    String json = JsonUtils.objToJson(retMap);  Map r = JsonUtils.json2Map(json);  System.out.println(r.get("callId123"));     }}