java对象转换为JSON字符串

JSON 入门指南

package com.javaeedev.util;

import java.util.Map;
import java.util.Set;

/**
 * Util for converting Java object to JSON string.
 * 
 * @author Xuefeng
 */
public final class JsonUtil {

    /**
     * Convert a Java object to JSON string.
     */
    @SuppressWarnings("unchecked")
    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);
        if (o instanceof int[])
            return intArray2Json((int[])o);
        if (o instanceof boolean[])
            return booleanArray2Json((boolean[])o);
        if (o instanceof long[])
            return longArray2Json((long[])o);
        if (o instanceof float[])
            return floatArray2Json((float[])o);
        if (o instanceof double[])
            return doubleArray2Json((double[])o);
        if (o instanceof short[])
            return shortArray2Json((short[])o);
        if (o instanceof byte[])
            return byteArray2Json((byte[])o);
        throw new RuntimeException("Unsupported type: " + o.getClass().getName());
    }

    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(',');
        }
        // set last ',' to ']':
        sb.setCharAt(sb.length()-1, ']');
        return sb.toString();
    }

    static String intArray2Json(int[] array) {
        if (array.length==0)
            return "[]";
        StringBuilder sb = new StringBuilder(array.length << 4);
        sb.append('[');
        for (int o : array) {
            sb.append(Integer.toString(o));
            sb.append(',');
        }
        // set last ',' to ']':
        sb.setCharAt(sb.length()-1, ']');
        return sb.toString();
    }

    static String longArray2Json(long[] array) {
        if (array.length==0)
            return "[]";
        StringBuilder sb = new StringBuilder(array.length << 4);
        sb.append('[');
        for (long o : array) {
            sb.append(Long.toString(o));
            sb.append(',');
        }
        // set last ',' to ']':
        sb.setCharAt(sb.length()-1, ']');
        return sb.toString();
    }

    static String booleanArray2Json(boolean[] array) {
        if (array.length==0)
            return "[]";
        StringBuilder sb = new StringBuilder(array.length << 4);
        sb.append('[');
        for (boolean o : array) {
            sb.append(Boolean.toString(o));
            sb.append(',');
        }
        // set last ',' to ']':
        sb.setCharAt(sb.length()-1, ']');
        return sb.toString();
    }

    static String floatArray2Json(float[] array) {
        if (array.length==0)
            return "[]";
        StringBuilder sb = new StringBuilder(array.length << 4);
        sb.append('[');
        for (float o : array) {
            sb.append(Float.toString(o));
            sb.append(',');
        }
        // set last ',' to ']':
        sb.setCharAt(sb.length()-1, ']');
        return sb.toString();
    }

    static String doubleArray2Json(double[] array) {
        if (array.length==0)
            return "[]";
        StringBuilder sb = new StringBuilder(array.length << 4);
        sb.append('[');
        for (double o : array) {
            sb.append(Double.toString(o));
            sb.append(',');
        }
        // set last ',' to ']':
        sb.setCharAt(sb.length()-1, ']');
        return sb.toString();
    }

    static String shortArray2Json(short[] array) {
        if (array.length==0)
            return "[]";
        StringBuilder sb = new StringBuilder(array.length << 4);
        sb.append('[');
        for (short o : array) {
            sb.append(Short.toString(o));
            sb.append(',');
        }
        // set last ',' to ']':
        sb.setCharAt(sb.length()-1, ']');
        return sb.toString();
    }

    static String byteArray2Json(byte[] array) {
        if (array.length==0)
            return "[]";
        StringBuilder sb = new StringBuilder(array.length << 4);
        sb.append('[');
        for (byte o : array) {
            sb.append(Byte.toString(o));
            sb.append(',');
        }
        // set last ',' to ']':
        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(',');
        }
        // set last ',' to '}':
        sb.setCharAt(sb.length()-1, '}');
        return sb.toString();
    }

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

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

    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();
    }
}

利用Jackson对Object,Map,List,数组,枚举,日期类等转化为json