java对象转json格式

  1 package com;
  2 
  3 import java.util.ArrayList;
  4 import java.util.HashMap;
  5 import java.util.List;
  6 import java.util.Map;
  7 import java.util.Set;
  8 
  9 import org.junit.Test;
 10 
 11 public class TestJson {
 12     
 13     static String string2Json(String s) {
 14         StringBuilder sb = new StringBuilder(s.length() + 20);
 15         sb.append(‘\"‘);
 16         for (int i = 0; i < s.length(); i++) {
 17             char c = s.charAt(i);
 18             switch (c) {
 19             case ‘\"‘:
 20                 sb.append("\\\"");
 21                 break;
 22             case ‘\\‘:
 23                 sb.append("\\\\");
 24                 break;
 25             case ‘/‘:
 26                 sb.append("\\/");
 27                 break;
 28             case ‘\b‘:
 29                 sb.append("\\b");
 30                 break;
 31             case ‘\f‘:
 32                 sb.append("\\f");
 33                 break;
 34             case ‘\n‘:
 35                 sb.append("\\n");
 36                 break;
 37             case ‘\r‘:
 38                 sb.append("\\r");
 39                 break;
 40             case ‘\t‘:
 41                 sb.append("\\t");
 42                 break;
 43             default:
 44                 sb.append(c);
 45             }
 46         }
 47         sb.append(‘\"‘);
 48         return sb.toString();
 49     }
 50 
 51     static String number2Json(Number number) {
 52         return number.toString();
 53     }
 54 
 55     static String boolean2Json(Boolean bool) {
 56         return bool.toString();
 57     }
 58 
 59     static String array2Json(Object[] array) {
 60         if (array.length == 0)
 61             return "[]";
 62         StringBuilder sb = new StringBuilder(array.length << 4);
 63         sb.append(‘[‘);
 64         for (Object o : array) {
 65             sb.append(toJson(o));
 66             sb.append(‘,‘);
 67         }
 68         // 将最后添加的 ‘,‘ 变为 ‘]‘:
 69         sb.setCharAt(sb.length() - 1, ‘]‘);
 70         return sb.toString();
 71     }
 72 
 73     static String map2Json(Map<String, Object> map) {
 74         if (map.isEmpty())
 75             return "{}";
 76         StringBuilder sb = new StringBuilder(map.size() << 4);
 77         sb.append(‘{‘);
 78         Set<String> keys = map.keySet();
 79         for (String key : keys) {
 80             Object value = map.get(key);
 81             sb.append(‘\"‘);
 82             sb.append(key);
 83             sb.append(‘\"‘);
 84             sb.append(‘:‘);
 85             sb.append(toJson(value));
 86             sb.append(‘,‘);
 87         }
 88         // 将最后的 ‘,‘ 变为 ‘}‘:
 89         sb.setCharAt(sb.length() - 1, ‘}‘);
 90         return sb.toString();
 91     }
 92 
 93     public static String toJson(Object o) {
 94         if (o == null)
 95             return "null";
 96         if (o instanceof String)
 97             return string2Json((String) o);
 98         if (o instanceof Boolean)
 99             return boolean2Json((Boolean) o);
100         if (o instanceof Number)
101             return number2Json((Number) o);
102         if (o instanceof Map)
103             return map2Json((Map<String, Object>) o);
104         if (o instanceof Object[])
105             return array2Json((Object[]) o);
106         throw new RuntimeException("Unsupported type: "
107                 + o.getClass().getName());
108     }
109 
110     @Test(expected = StackOverflowError.class)
111     public void testRecurrsiveMap2Json() {
112         Map<String, Object> map = new HashMap<String, Object>();
113         map.put("key", "value");
114         map.put("key2", 2);
115         List<Integer> array = new ArrayList<Integer>();
116          array.add(1); 
117          array.add(2);
118         map.put("array", array);
119         String json = TestJson.toJson(map);
120         System.out.println(json);
121     }
122 }