JSON補助クラスは、いくつかのオブジェクトと集合を標準的なJSONフォーマットに変換できます.

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;   
  
/**  
 *       JSON     JSON        
 *   
 * @date 2008/05/07  
 * @version 1.0.0  
 */  
public class JsonUtil {   
  /** Commons Logging instance. */  
  private static org.apache.commons.logging.Log log = org.apache.commons.logging.LogFactory   
      .getLog(JsonUtil.class);   
  
  /**  
   * @param obj       
   * @return String  
   */  
  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();   
  }   
  
  /**  
   * @param bean bean    
   * @return String  
   */  
  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();   
  }   
  
  /**  
   * @param list list    
   * @return String  
   */  
  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();   
  }   
  
  /**  
   * @param array       
   * @return String  
   */  
  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();   
  }   
  
  /**  
   * @param map map    
   * @return String  
   */  
  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();   
  }   
  
  /**  
   * @param set       
   * @return String  
   */  
  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();   
  }   
  
  /**  
   * @param s     
   * @return String  
   */  
  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 '
':   
        sb.append("\
");   
        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();   
  }   
}