java中对象转换为json

网上找的一个类，感觉挺实用的，就贴在这里。

package cn.jasgroup.sanjiangaerolng.devicetest.tree;

import java.beans.IntrospectionException;
import java.beans.Introspector;
import java.beans.PropertyDescriptor;
import java.math.BigDecimal;
import java.math.BigInteger;
import java.util.List;
import java.util.Map;
import java.util.Set;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

public class JsonUtil {
    private static Log log = LogFactory.getLog(JsonUtil.class);
    public static String object2json(Object obj) {
        StringBuilder json = new StringBuilder();
        if (obj == null) {
            json.append("\"\"");
        } else if (obj instanceof String || obj instanceof Integer || obj instanceof Float || obj instanceof Boolean || obj instanceof Short || obj instanceof Double || obj instanceof Long || obj instanceof BigDecimal || obj instanceof BigInteger || obj instanceof Byte) {
            json.append("\"").append(string2json(obj.toString())).append("\"");
        } else if (obj instanceof Object[]) {
            json.append(array2json((Object[]) obj));
        } else if (obj instanceof List) {
            json.append(list2json((List<?>) obj));
        } else if (obj instanceof Map) {
            json.append(map2json((Map<?, ?>) obj));
        } else if (obj instanceof Set) {
            json.append(set2json((Set<?>) obj));
        } else {
            json.append(bean2json(obj));
        }
        return json.toString();
    }
    public static String bean2json(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 = object2json(props[i].getName());
                    String value = object2json(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();
    }
    public static String list2json(List<?> list) {
        StringBuilder json = new StringBuilder();
        json.append("[");
        if (list != null && list.size() > 0) {
            for (Object obj : list) {
                json.append(object2json(obj));
                json.append(",");
            }
            json.setCharAt(json.length() - 1, ']');
        } else {
            json.append("]");
        }
        return json.toString();
    }
    public static String array2json(Object[] array) {
        StringBuilder json = new StringBuilder();
        json.append("[");
        if (array != null && array.length > 0) {
            for (Object obj : array) {
                json.append(object2json(obj));
                json.append(",");
            }
            json.setCharAt(json.length() - 1, ']');
        } else {
            json.append("]");
        }
        return json.toString();
    }
    public static String map2json(Map<?, ?> map) {
        StringBuilder json = new StringBuilder();
        json.append("{");
        if (map != null && map.size() > 0) {
            for (Object key : map.keySet()) {
                json.append(object2json(key));
                json.append(":");
                json.append(object2json(map.get(key)));
                json.append(",");
            }
            json.setCharAt(json.length() - 1, '}');
        } else {
            json.append("}");
        }
        return json.toString();
    }
    public static String set2json(Set<?> set) {
        StringBuilder json = new StringBuilder();
        json.append("[");
        if (set != null && set.size() > 0) {
            for (Object obj : set) {
                json.append(object2json(obj));
                json.append(",");
            }
            json.setCharAt(json.length() - 1, ']');
        } else {
            json.append("]");
        }
        return json.toString();
    }
    public static String string2json(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 void main(String args[]) {
//        List<UserTest> userList = new ArrayList<UserTest>();
//        userList.add(new UserTest("linbo","北京服装学院",25));
//        StringBuilder sb = new StringBuilder();
//        System.out.println(list2json(userList));
    }
}