浅谈Android数据库CRUD操作的封装与实现（二）【Android Hibernate，永别了SQL！】
用了一整天的时间把昨天遗留下来的问题解决了。
既然是要做一个类似Hibernate的工具，最主要的就是尽量减少SQL语句的编写。我采用反向强力解析实体类的办法，实现了自动构建SQL语句的功能。
现在有三个核心类：
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EntityDao是一个泛型接口，定义了所有应该实现的方法。SimpleDao是抽象类，对接口功能进行实现，真正实体的DAO只要继承SimpleDao就可以拥有所有功能。无需任何额外实现、无需任何SQL语句！
首先，看看我的BeanTools。它主要负责对实体进行强力解析，废话不多说，上代码：
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/** * Bean工具类 * @author EwinLive * */public abstract class BeanTools {/** * 获取第一个泛型类 */public static Class<?> getGenericClass(Class<?> clazz) {return getGenericClass(clazz, 0);}/** * 获取泛型类 */public static Class<?> getGenericClass(Class<?> clazz, int index) throws IndexOutOfBoundsException {Type genType = clazz.getGenericSuperclass();if (!(genType instanceof ParameterizedType)) {return Object.class;}Type[] params = ((ParameterizedType) genType).getActualTypeArguments();if (index >= params.length || index < 0) {throw new IndexOutOfBoundsException("Index: " + index + ", Size of Parameterized Type: " + params.length);}return (Class<?>) params[index];}/** * 直接设置对象属性值, 无视private/protected修饰符, 不经过setter函数. */public static void setFieldValue(final Object object, final String fieldName, final Object value) {Field field = getDeclaredField(object, fieldName);if (field == null) {throw new IllegalArgumentException("Could not find field [" + fieldName + "] on target [" + object + "]");}makeAccessible(field);try {field.set(object, value);} catch (IllegalAccessException e) {//logger.error("不可能抛出的异常:{}", e.getMessage());}}/** * 强行设置Field可访问. */protected static void makeAccessible(final Field field) {if (!Modifier.isPublic(field.getModifiers()) || !Modifier.isPublic(field.getDeclaringClass().getModifiers())) {field.setAccessible(true);}}/** * 循环向上转型, 获取对象的DeclaredField. * * 如向上转型到Object仍无法找到, 返回null. */protected static Field getDeclaredField(final Object object, final String fieldName) {//Assert.notNull(object, "object不能为空");//Assert.hasText(fieldName, "fieldName");for (Class<?> superClass = object.getClass(); superClass != Object.class; superClass = superClass.getSuperclass()) {try {return superClass.getDeclaredField(fieldName);} catch (NoSuchFieldException e) {// Field不在当前类定义,继续向上转型}}return null;}/** * 转换字符串到相应类型. * * @param value 待转换的字符串 * @param toType 转换目标类型 */public static Object convertStringToObject(String value, Class<?> toType) {if (StringTools.isNotEmpty(value)) {return ConvertUtils.convert(value, toType);} else {return null;}}/** * 强行获取私有属性的值 */public static Object getPrivateProperty(Object object, String propertyName) throws IllegalAccessException, NoSuchFieldException {//Assert.notNull(object);//Assert.hasText(propertyName);Field field = object.getClass().getDeclaredField(propertyName);field.setAccessible(true);return field.get(object);}/** * 强行设置私有属性的值 */public static void setPrivateProperty(Object object, String propertyName, Object newValue) throws IllegalAccessException, NoSuchFieldException {//Assert.notNull(object);//Assert.hasText(propertyName);Field field = object.getClass().getDeclaredField(propertyName);field.setAccessible(true);field.set(object, newValue);}/** * 获取所有字段 * @param entityClass 实体的类型 * @return data * 返回包含两个数组的HashMap，可参考以下使用方法： * String[] fieldName = (String[]) data.get("fieldName"); * Class<?>[] fieldType = (Class<?>[]) data.get("fieldType"); */public static HashMap<Object, Object> getAllFiled(Class<?> entityClass){HashMap<Object, Object> data = new HashMap<Object, Object>();Field[] fields = entityClass.getDeclaredFields();String[] fieldName = new String[fields.length];Class<?>[] fieldType = new Class<?>[fields.length];for(int i=0; i<fields.length; i++){fieldName[i] = fields[i].getName();//组装名称数组fieldType[i] = fields[i].getType();//组装类型数组}data.put("fieldName", fieldName);data.put("fieldType", fieldType);return data;}}?呵呵，有了它就可以无视神马private、神马protected了，所向无敌！
EntityDao接口就不多说了，现在我们来实现SimpleDao，这是重头戏。我的思路是根据子类具体提供的实体类型进行强力解析，获取所有字段以及字段的类型。完全自动构建SQl语句。由于保存、更新实体的语句变化不会很大，我只在实例化DAO对象时进行初始化。
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/** * 实现了EntityDao接口,其他实体DAO只要继承它即可拥有所有强大功能。 * @author EwinLive * * @param <T> * @param <PK> */public abstract class SimpleDao<T, PK extends Serializable> implements EntityDao<T, PK> {/** * 实体的类型 */protected Class<T> entityClass;/** * 表名 */protected String tableName;/** * 数据库管理器 */protected DataBaseHelper dbHelper;/** * 保存实体所要执行的SQL语句 * 只在创建对象时初始化。 */protected String saveSql;/** * 更新实体所要执行的SQL语句 * 只在创建对象时初始化。 */protected String updateSql;/** * 字段在数据表中所对应的列的索引 * 只在创建对象时初始化。 */protected int[] fieldPostion;public String getTableName() {return tableName;}public void setTableName(String tableName) {this.tableName = tableName;}public DataBaseHelper getDbHelper() {return dbHelper;}public void setDbHelper(DataBaseHelper dbHelper) {this.dbHelper = dbHelper;}public String getSaveSql() {return saveSql;}public void setSaveSql(String saveSql) {this.saveSql = saveSql;}public String getUpdateSql() {return updateSql;}public void setUpdateSql(String updateSql) {this.updateSql = updateSql;}/** * 专属构造器 * 可通过子类的范型定义取得对象类型Class. * @param tableName 实体对应的表名 * @param context 设备上下文，通常是一个Activity对象 */@SuppressWarnings("unchecked")public SimpleDao(String tableName, Context context) {this.entityClass = (Class<T>) BeanTools.getGenericClass(getClass());this.tableName = tableName;this.dbHelper = new DataBaseHelper(context);this.saveSql = initSaveSql();this.updateSql = initUpdateSql();this.fieldPostion = initFieldPostion();}@Overridepublic void save(T entity) throws Exception {dbHelper.getReadableDatabase().execSQL(saveSql, getSaveValue(entity));}@SuppressWarnings("unused")@Overridepublic void remove(PK... ids) {if(ids.length > 0){StringBuffer sb = new StringBuffer();for(PK id : ids){sb.append('?').append(',');}sb.deleteCharAt(sb.length() - 1);dbHelper.getReadableDatabase().execSQL("delete from "+ tableName +" where id in(" + sb + ")", (Object[]) ids);}}@Overridepublic void upDate(T entity) throws Exception {dbHelper.getReadableDatabase().execSQL(updateSql, getUpdateValue(entity));}@Overridepublic T find(PK id) {Cursor cursor = dbHelper.getReadableDatabase().rawQuery("select * from " + tableName + " where id=?", new String[]{String.valueOf(id)});cursor.moveToNext();return getEntityFromCursor(cursor);}@Overridepublic List<T> getScroolData(Integer startResult, Integer maxResult){List<T> list = new ArrayList<T>(0);Cursor cursor = dbHelper.getReadableDatabase().rawQuery("select * from " + tableName + " limit ?, ?", new String[]{String.valueOf(startResult), String.valueOf(maxResult)});while(cursor.moveToNext()){list.add(getEntityFromCursor(cursor));}return list;}@Overridepublic Long getCount() {Cursor cursor = dbHelper.getReadableDatabase().rawQuery("select count(*) from " + tableName, null);if(cursor.moveToNext())return cursor.getLong(0);return 0l;}/** * 初始化保存实体所需的SQL语句 * @return */@SuppressWarnings("rawtypes")protected String initSaveSql(){HashMap data = BeanTools.getAllFiled(entityClass);String[] fieldName = (String[]) data.get("fieldName");StringBuffer bufferName = new StringBuffer();StringBuffer bufferExpr = new StringBuffer();for(String tmp : fieldName){bufferName.append(tmp).append(',');bufferExpr.append("?,");}//去除id字段及其属性值bufferName.delete(bufferName.indexOf("id"), bufferName.indexOf("id")+3);bufferExpr.delete(0, 2);//去除多余的分隔符bufferName.deleteCharAt(bufferName.length()-1);bufferExpr.deleteCharAt(bufferExpr.length()-1);String sql = "insert into "+ tableName+ "(" + bufferName.toString() + ") values(" + bufferExpr.toString() + ")";return sql;}/** * 初始化更新实体所需的SQL语句 * @return */@SuppressWarnings("rawtypes")protected String initUpdateSql(){HashMap data = BeanTools.getAllFiled(entityClass);String[] fieldName = (String[]) data.get("fieldName");StringBuffer sqlBuffer = new StringBuffer();sqlBuffer.append("update "+ tableName + " set ");for(String tmp : fieldName){sqlBuffer.append(tmp).append("=?, ");}//去除id字段及其属性值sqlBuffer.delete(sqlBuffer.indexOf(" id=?"), sqlBuffer.indexOf("id") + 5);sqlBuffer.deleteCharAt(sqlBuffer.length()-2);sqlBuffer.append("where id =?");return sqlBuffer.toString();}/** * 获取保存实体所需的值 * @param entity * @return * @throws IllegalAccessException * @throws NoSuchFieldException */@SuppressWarnings("rawtypes")protected Object[] getSaveValue(T entity) throws IllegalAccessException, NoSuchFieldException{HashMap data = BeanTools.getAllFiled(entityClass);String[] fieldName = (String[]) data.get("fieldName");Object[] values;int length = fieldName.length;values = new Object[length-1];int j=0;for(int i=0; i<length; i++){if("id".equals(fieldName[i].toString())){continue;//跳过ID字段}values[j++] = BeanTools.getPrivateProperty(entity, fieldName[i]);}return values;}/** * 获取更新实体所需的值 * @param entity * @return * @throws IllegalAccessException * @throws NoSuchFieldException */@SuppressWarnings("rawtypes")protected Object[] getUpdateValue(T entity) throws Exception{HashMap data = BeanTools.getAllFiled(entityClass);String[] fieldName = (String[]) data.get("fieldName");Object[] values;int length = fieldName.length;values = new Object[length-1];int j=0;int id=0;for(int i=0; i<length; i++){if("id".equals(fieldName[i].toString())){id = (Integer) BeanTools.getPrivateProperty(entity, fieldName[i]);continue;//跳过ID字段}values[j++] = BeanTools.getPrivateProperty(entity, fieldName[i]);}Object[] values2 = new Object[length];System.arraycopy(values, 0, values2, 0, values.length);values2[length-1] = id;return values2;}/** * 初始化字段在数据表中 对应的索引 * @param cursor */@SuppressWarnings("rawtypes")protected int[] initFieldPostion(){HashMap data = BeanTools.getAllFiled(entityClass);String[] fieldName = (String[]) data.get("fieldName");int length = fieldName.length;int[] postion = new int[length];Cursor cursor = dbHelper.getReadableDatabase().rawQuery("select * from " + tableName + " limit ?, ?", new String[]{"0", "2"});for(int i =0; i<length; i++){postion[i] = cursor.getColumnIndex(fieldName[i]);}return postion;}/** * 从游标中获取实体 * @param cursor 游标 * @return T 实体对象 */@SuppressWarnings("rawtypes")public T getEntityFromCursor(Cursor cursor){HashMap data = BeanTools.getAllFiled(entityClass);String[] fieldName = (String[]) data.get("fieldName");Class<?>[] fieldType = (Class<?>[]) data.get("fieldType");int length = fieldName.length;T entity = null;String db_data;String fieldTypeName;try {entity = entityClass.newInstance();for(int i=0;i<length;i++){fieldTypeName = fieldType[i].getSimpleName();db_data = cursor.getString(fieldPostion[i]);if(null != db_data){if("String".equals(fieldTypeName)){BeanTools.setFieldValue(entity, fieldName[i], db_data);}else if("int".equals(fieldTypeName)){BeanTools.setFieldValue(entity, fieldName[i], Integer.parseInt(db_data));}else if("long".equals(fieldTypeName)){BeanTools.setFieldValue(entity, fieldName[i], Long.getLong(db_data));}else if("float".equals(fieldTypeName)){BeanTools.setFieldValue(entity, fieldName[i],Float.parseFloat(db_data));}}}} catch (Exception e) {System.out.println(e.getMessage());}return entity;}}??
好了现在大部分工作都已经完成了。在你的项目中，有多少个实体就创建几个DAO吧，只要继承SimpleDao就行了！（注意填上具体对应的实体类型）比如：
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public class SimpleMessageDao extends SimpleDao<SimpleMessage, Integer> {/** * 定义该实体对应数据库的表名 */public static final String TABLE_NAME = "simple_message";/** * 简化的构造器 * @param context */public SimpleMessageDao(Context context) {this(TABLE_NAME, context);}/** * 重写父类的构造器 * @param tableName * @param context */public SimpleMessageDao(String tableName, Context context) {super(TABLE_NAME, context);}}??对，仅仅是继承就足够了！
你现在就可以随便 new XXXDao（context）了，他已经可以帮你进行增删改查的操作。是不是忒方便了！
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============================完整原创，你可以随意使用其中的代码，但请遵循开源精神！============================
1 楼 稍纵即逝 2010-12-07 实用价值很高，正好可以拿来用，谢谢……