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 '':
                sb.append("\b");
                break;
            case 'f':
                sb.append("\f");
                break;
            case '
':
                sb.append("\n");
                break;
            case '
':
                sb.append("\r");
                break;
            case '	':
                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