java对象转json格式

 package com;

 import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;

 import org.junit.Test;

 public class TestJson {

     static String string2Json(String s) {
         StringBuilder sb = new StringBuilder(s.length() + 20);
         sb.append('\"');
         for (int i = 0; i < s.length(); i++) {
             char c = s.charAt(i);
             switch (c) {
             case '\"':
                 sb.append("\\\"");
                 break;
             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;
             default:
                 sb.append(c);
             }
         }
         sb.append('\"');
         return sb.toString();
     }

     static String number2Json(Number number) {
         return number.toString();
     }

     static String boolean2Json(Boolean bool) {
         return bool.toString();
     }

     static String array2Json(Object[] array) {
         if (array.length == 0)
             return "[]";
         StringBuilder sb = new StringBuilder(array.length << 4);
         sb.append('[');
         for (Object o : array) {
             sb.append(toJson(o));
             sb.append(',');
         }
         // 将最后添加的 ',' 变为 ']':
         sb.setCharAt(sb.length() - 1, ']');
         return sb.toString();
     }

     static String map2Json(Map<String, Object> map) {
         if (map.isEmpty())
             return "{}";
         StringBuilder sb = new StringBuilder(map.size() << 4);
         sb.append('{');
         Set<String> keys = map.keySet();
         for (String key : keys) {
             Object value = map.get(key);
             sb.append('\"');
             sb.append(key);
             sb.append('\"');
             sb.append(':');
             sb.append(toJson(value));
             sb.append(',');
         }
         // 将最后的 ',' 变为 '}':
         sb.setCharAt(sb.length() - 1, '}');
         return sb.toString();
     }

     public static String toJson(Object o) {
         if (o == null)
             return "null";
         if (o instanceof String)
             return string2Json((String) o);
         if (o instanceof Boolean)
             return boolean2Json((Boolean) o);
         if (o instanceof Number)
             return number2Json((Number) o);
         if (o instanceof Map)
             return map2Json((Map<String, Object>) o);
         if (o instanceof Object[])
             return array2Json((Object[]) o);
         throw new RuntimeException("Unsupported type: "
                 + o.getClass().getName());
     }

     @Test(expected = StackOverflowError.class)
     public void testRecurrsiveMap2Json() {
         Map<String, Object> map = new HashMap<String, Object>();
         map.put("key", "value");
         map.put("key2", 2);
         List<Integer> array = new ArrayList<Integer>();
          array.add(1);
          array.add(2);
         map.put("array", array);
         String json = TestJson.toJson(map);
         System.out.println(json);
     }
 }

参考文献：

http://www.ibm.com/developerworks/cn/web/wa-lo-json/

http://www.w3school.com.cn/json/index.asp