早前一直对单例模式和静态工具类的功能重叠有些疑惑，昨天做了一个功能，忽然发现了一些单例可以实现但是静态工具类无法满足的需求。
我有一个接口IAuthorization：
View Code
/** * 所有需要配置权限的功能块都必须实现本接口 * * @author caiyu * @date Nov 16, 2012 9:36:49 AM * */ public interface IAuthorization { // 权限开关 false有验证，true无验证 public static final boolean open = false; String XML_NEW = "new"; String XML_DELETE = "delete"; String XML_MODIFY = "modify"; String XML_DEPLOY = "deploy"; String XML_COMPILE = "compile"; String XML_SYNC = "sync"; String XML_EXPORT = "export"; String XML_EXPORT_DETAIL = "export_detail"; String XML_BROWSE = "browse"; String EXT_TCD = "tcd"; String EXT_BCD = "bcd"; String EXT_TRD = "trd"; String EXT_TWF = "twf"; String EXT_TMPL = "tmpl"; String EXT_DICT = "dict"; String EXT_F_PROJECT = "folder_project"; String EXT_F_APPLICATION = "folder_application"; String EXT_FPCK = "fpck"; String EXT_NATP = "pck"; /** * 注册权限委托 * * @return */ IAuthDelegate registerDelegate(); /** * 处理权限委托 * * @param delegate * 委托 * @param selection * @return 是否具备权限 */ boolean handleDelegate(IAuthDelegate delegate, Object selection); }
要使用权限管理的类必须实现该接口，现在我有两个编辑器（Editor）需要被权限管理，当没有编辑权限的时候，将该编辑器置为不可编辑状态。由于以后编辑器会不停的增加，所以需要使用一个通用的IAuthorization的工具类来实现权限管理。
既然是工具类，那么就说明我们不需要多个实例，就应该使用单例或是或是静态工具类了。
既然是实现自IAuthorization，就限定了该类的实现方法不能为static，于是单例模式应用就呼之欲出了。
看看实现：
------------------------------------下面是SB的实现，不要看----------------------------
public class PacketAuthManager implements IAuthorization { public final static PacketAuthManager INSTANCE; static{ INSTANCE=new PacketAuthManager(); } protected IActionAuthDelegate authDele; private String actionPermCode; private PacketAuthManager() { authDele = (IActionAuthDelegate) registerDelegate(); actionPermCode = AuthCodeUtil.calculateActionPermCode(XML_MODIFY); } @Override public IAuthDelegate registerDelegate() { return AuthDelegateFactory.newDelegate(AuthDelegateFactory.TYPE_ACTION); } public boolean handleDelegate(String resource) { return handleDelegate(authDele, resource); } @Override public boolean handleDelegate(IAuthDelegate delegate, Object selection) { String resourceCode = null; if (selection instanceof String) { resourceCode = AuthCodeUtil .calculateResourcePermCode((String) selection); } delegate.setPermIDs(new String[] { AuthCodeUtil.calculatePermissionId( actionPermCode, resourceCode) }); AuthController.getInstance().handleDelegate(delegate); return ((IActionAuthDelegate) delegate).isActionEnabled() || open; } }
-----------------------------------后面才是正确的实现------------------------------------------
/** * 通用SQL类型工具 * * @author caiyu * @date 2013 2013-7-15 上午10:54:17 */ public final class GenericSqlTypeUtil { private static GenericSqlTypeUtil INSTANCE; private final static String TEMPLATE = "/genericSqlType.xml"; private final Map<String, String> genericSqlTypeCache; private GenericSqlTypeUtil() { genericSqlTypeCache = new HashMap<String, String>(); init(); } /** * 初始化 */ private void init() { SAXReader reader = null; Document doc = null; InputStream is = null; try { is = FileLocator.openStream(Activator.getDefault().getBundle(), new Path(TEMPLATE), false); // is = new FileInputStream(TEMPLATE); reader = new SAXReader(); doc = reader.read(is); // TODO // 对genericSqlTypeCache做初始化，genericSqlTypeCache的KEY为取自name，VALUE取自desc Element root = doc.getRootElement(); List<?> list = root.elements("type"); for (Object o : list) { Element element = (Element) o; String name = element.attributeValue("name"); String desc = element.elementText("desc"); genericSqlTypeCache.put(name, desc); } } catch (IOException e) { e.printStackTrace(); } catch (DocumentException e) { e.printStackTrace(); } finally { if (reader != null) reader.resetHandlers(); if (doc != null) doc.clearContent(); if (is != null) try { is.close(); } catch (IOException e) { e.printStackTrace(); } } } /** * 根据通用的SQL类型名称获取类型描述 * * @param genericSqlTypeName * 参考java.sql.Types * @return */ public String getSqlTypeDescription(String genericSqlTypeName) { return genericSqlTypeCache.get(genericSqlTypeName); } public static GenericSqlTypeUtil getInstance() { if (INSTANCE == null) INSTANCE = new GenericSqlTypeUtil(); return INSTANCE; } }
