注解+反射+JDBC，实现一个简易的泛型DAO接口

 

 

一、实现思路

      1、定义3个Annotation（注解）：Entity、Id、Column，Entity作用于Type级别，用于标识JavaBean与数据库表名的映射关系。Id作用于Field级别，用于标识JavaBean中ID属性与表中ID字段的映射关系，Column作用于Field级别，用于标识JavaBean中除ID属性外的其它属性与表中字段的映射关系。

     2、在Dao实现类中，通过反射API获得JavaBean中注解和属性的信息，如：表名、字段。JavaBean属性的名称、数据类型等信息。然后将这些信息拼接成一条SQL语句，通过JDBC的方式与数据库交互。

二、示例代码

1、定义一个Dao公共类，提供获得数据库连接与释放数据库资源的接口

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1. package dao; 
2.  
3. import java.sql.Connection; 
4. import java.sql.DriverManager; 
5. import java.sql.PreparedStatement; 
6. import java.sql.ResultSet; 
7. import java.sql.SQLException; 
8.  
9. /**
10. * 提供获取数据库连接、释放资源的接口
11. */ 
12. public class JdbcDaoHelper { 
13.      
14.     /**
15.      * 数据库用户名
16.      */ 
17.     private staticfinal String USER = "test"; 
18.      
19.     /**
20.      * 数据库密码
21.      */ 
22.     private staticfinal String PASSWORD = "test"; 
23.      
24.     /**
25.      * 连接数据库的地址
26.      */ 
27.     private staticfinal String URL = "jdbc:oracle:thin:@127.0.0.1:1521:study"; 
28.      
29.     private static Connection conn; 
30.      
31.     /**
32.      * 获得一个数据库连接对象
33.      * @return java.sql.Connection实例
34.      */ 
35.     public static Connection getConnection() { 
36.         try { 
37.             if (conn == null) { 
38.                 Class.forName("oracle.jdbc.OracleDriver"); 
39.                 conn = DriverManager.getConnection(URL, USER, PASSWORD); 
40.             } else { 
41.                 return conn; 
42.             } 
43.         } catch (Exception e) { 
44.             e.printStackTrace(); 
45.         } 
46.         return conn; 
47.     } 
48.      
49.     /**
50.      * 释放数据库资源
51.      */ 
52.     public staticvoid release(PreparedStatement ps,ResultSet rs) { 
53.         try { 
54.             if (conn != null) { 
55.                 conn.close(); 
56.                 conn = null; 
57.             } 
58.             if (ps != null) { 
59.                 ps.close(); 
60.                 ps = null; 
61.             } 
62.             if (rs != null) { 
63.                 rs.close(); 
64.                 rs = null; 
65.             } 
66.         } catch (SQLException e) { 
67.             e.printStackTrace(); 
68.         } 
69.     } 
70. } 

package dao;import java.sql.Connection;import java.sql.DriverManager;import java.sql.PreparedStatement;import java.sql.ResultSet;import java.sql.SQLException;/** * 提供获取数据库连接、释放资源的接口 */public class JdbcDaoHelper {/** * 数据库用户名 */private static final String USER = "test";/** * 数据库密码  */private static final String PASSWORD = "test";/** * 连接数据库的地址 */private static final String URL = "jdbc:oracle:thin:@127.0.0.1:1521:study";private static Connection conn;/** * 获得一个数据库连接对象 * @return java.sql.Connection实例 */public static Connection getConnection() {try {if (conn == null) {Class.forName("oracle.jdbc.OracleDriver");conn = DriverManager.getConnection(URL, USER, PASSWORD);} else {return conn;}} catch (Exception e) {e.printStackTrace();}return conn;}/** * 释放数据库资源 */public static void release(PreparedStatement ps,ResultSet rs) {try {if (conn != null) {conn.close();conn = null;}if (ps != null) {ps.close();ps = null;}if (rs != null) {rs.close();rs = null;}} catch (SQLException e) {e.printStackTrace();}}}

2、定义一个泛型Dao接口GenericDao<T>

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1. package dao; 
2.  
3. import java.util.List; 
4. import java.util.Map; 
5.  
6. public interface GenericDao<T> { 
7.      
8.     public void save(T t)throws Exception; 
9.      
10.     public void delete(Object id,Class<T> clazz)throws Exception; 
11.      
12.     public void update(T t)throws Exception; 
13.      
14.     public T get(Object id,Class<T> clazz)throws Exception; 
15.      
16.     /**
17.      * 根据条件查询
18.      * @param sqlWhereMap key：条件字段名 value：条件字段值
19.      * @param clazz
20.      * @return
21.      * @throws Exception
22.      */ 
23.     public List<T> findAllByConditions(Map<String,Object> sqlWhereMap,Class<T> clazz)throws Exception; 
24.      
25. } 

package dao;import java.util.List;import java.util.Map;public interface GenericDao<T> {public void save(T t) throws Exception;public void delete(Object id,Class<T> clazz) throws Exception;public void update(T t) throws Exception;public T get(Object id,Class<T> clazz) throws Exception;/** * 根据条件查询 * @param sqlWhereMap key：条件字段名 value：条件字段值 * @param clazz * @return * @throws Exception */public List<T> findAllByConditions(Map<String,Object> sqlWhereMap,Class<T> clazz) throws Exception;}

3、定义GenericDao<T>接口JDBC实现类JdbcGenericDaoImpl<T>

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1. package dao; 
2.  
3. import java.beans.IntrospectionException; 
4. import java.beans.PropertyDescriptor; 
5. import java.lang.reflect.Field; 
6. import java.lang.reflect.InvocationTargetException; 
7. import java.sql.PreparedStatement; 
8. import java.sql.ResultSet; 
9. import java.sql.SQLException; 
10. import java.sql.Timestamp; 
11. import java.sql.Types; 
12. import java.util.ArrayList; 
13. import java.util.Date; 
14. import java.util.HashMap; 
15. import java.util.Iterator; 
16. import java.util.List; 
17. import java.util.Map; 
18. import java.util.Set; 
19. import java.util.Map.Entry; 
20.  
21. import annotation.Column; 
22. import annotation.Entity; 
23. import annotation.Id; 
24. import exception.NotFoundAnnotationException; 
25.  
26. /**
27. * 泛型DAO的JDBC实现
28. * @author 杨信
29. * @version 1.0
30. */ 
31. public class JdbcGenericDaoImpl<T>implements GenericDao<T> { 
32.      
33.     //表的别名 
34.     private staticfinal String TABLE_ALIAS = "t"; 
35.  
36.     @Override 
37.     public void save(T t)throws Exception { 
38.         Class<?> clazz = t.getClass(); 
39.         //获得表名 
40.         String tableName = getTableName(clazz); 
41.         //获得字段 
42.         StringBuilder fieldNames = new StringBuilder();    //字段名 
43.         List<Object> fieldValues = new ArrayList<Object>();//字段值 
44.         StringBuilder placeholders = new StringBuilder();  //占位符 
45.         Field[] fields = clazz.getDeclaredFields(); 
46.         for (Field field : fields) { 
47.             PropertyDescriptor pd = new PropertyDescriptor(field.getName(),t.getClass()); 
48.             if (field.isAnnotationPresent(Id.class)) { 
49.                 fieldNames.append(field.getAnnotation(Id.class).value()).append(","); 
50.                 fieldValues.add(pd.getReadMethod().invoke(t)); 
51.             } else if(field.isAnnotationPresent(Column.class)) { 
52.                 fieldNames.append(field.getAnnotation(Column.class).value()).append(","); 
53.                 fieldValues.add(pd.getReadMethod().invoke(t)); 
54.             } 
55.             placeholders.append("?").append(","); 
56.         } 
57.         //删除最后一个逗号 
58.         fieldNames.deleteCharAt(fieldNames.length()-1); 
59.         placeholders.deleteCharAt(placeholders.length()-1); 
60.          
61.         //拼接sql 
62.         StringBuilder sql = new StringBuilder(""); 
63.         sql.append("insert into ").append(tableName) 
64.            .append(" (").append(fieldNames.toString()) 
65.            .append(") values (").append(placeholders).append(")") ; 
66.         PreparedStatement ps = JdbcDaoHelper.getConnection().prepareStatement(sql.toString()); 
67.         //设置SQL参数占位符的值 
68.         setParameter(fieldValues, ps, false); 
69.         //执行SQL 
70.         ps.execute(); 
71.         JdbcDaoHelper.release(ps, null); 
72.          
73.         System.out.println(sql + "\n" + clazz.getSimpleName() +"添加成功!"); 
74.     } 
75.  
76.  
77.     @Override 
78.     public void delete(Object id,Class<T> clazz)throws Exception { 
79.         //获得表名 
80.         String tableName = getTableName(clazz); 
81.         //获得ID字段名和值 
82.         String idFieldName = ""; 
83.         boolean flag = false; 
84.         Field[] fields = clazz.getDeclaredFields(); 
85.         for (Field field : fields) { 
86.             if(field.isAnnotationPresent(Id.class)) { 
87.                 idFieldName = field.getAnnotation(Id.class).value(); 
88.                 flag = true; 
89.                 break; 
90.             } 
91.         } 
92.         if (!flag) { 
93.             throw new NotFoundAnnotationException(clazz.getName() +" object not found id property."); 
94.         } 
95.          
96.         //拼装sql 
97.         String sql = "delete from " + tableName +" where " + idFieldName + "=?"; 
98.         PreparedStatement ps = JdbcDaoHelper.getConnection().prepareStatement(sql); 
99.         ps.setObject(1, id); 
100.         //执行SQL 
101.         ps.execute(); 
102.         JdbcDaoHelper.release(ps,null); 
103.          
104.         System.out.println(sql + "\n" + clazz.getSimpleName() +"删除成功!"); 
105.     } 
106.  
107.     @Override 
108.     public void update(T t)throws Exception { 
109.         Class<?> clazz = t.getClass(); 
110.         //获得表名 
111.         String tableName = getTableName(clazz); 
112.         //获得字段 
113.         List<Object> fieldNames = new ArrayList<Object>(); //字段名 
114.         List<Object> fieldValues = new ArrayList<Object>();//字段值 
115.         List<String> placeholders = new ArrayList<String>();//占位符 
116.         String idFieldName = ""; 
117.         Object idFieldValue = ""; 
118.         Field[] fields = clazz.getDeclaredFields(); 
119.         for (Field field : fields) { 
120.             PropertyDescriptor pd = new PropertyDescriptor(field.getName(),t.getClass()); 
121.             if (field.isAnnotationPresent(Id.class)) { 
122.                 idFieldName = field.getAnnotation(Id.class).value(); 
123.                 idFieldValue = pd.getReadMethod().invoke(t); 
124.             } else if(field.isAnnotationPresent(Column.class)) { 
125.                 fieldNames.add(field.getAnnotation(Column.class).value()); 
126.                 fieldValues.add(pd.getReadMethod().invoke(t)); 
127.                 placeholders.add("?"); 
128.             } 
129.         } 
130.         //ID作为更新条件，放在集合中的最后一个元素 
131.         fieldNames.add(idFieldName); 
132.         fieldValues.add(idFieldValue); 
133.         placeholders.add("?"); 
134.          
135.         //拼接sql 
136.         StringBuilder sql = new StringBuilder(""); 
137.         sql.append("update ").append(tableName).append(" set "); 
138.         int index = fieldNames.size() -1; 
139.         for (int i =0; i < index; i++) { 
140.             sql.append(fieldNames.get(i)).append("=").append(placeholders.get(i)).append(","); 
141.         } 
142.         sql.deleteCharAt(sql.length()-1).append(" where ").append(fieldNames.get(index)).append("=").append("?"); 
143.          
144.         //设置SQL参数占位符的值 
145.         PreparedStatement ps = JdbcDaoHelper.getConnection().prepareStatement(sql.toString()); 
146.         setParameter(fieldValues, ps, false); 
147.          
148.         //执行SQL 
149.         ps.execute(); 
150.         JdbcDaoHelper.release(ps, null); 
151.          
152.         System.out.println(sql + "\n" + clazz.getSimpleName() +"修改成功."); 
153.     } 
154.  
155.     @Override 
156.     public T get(Object id,Class<T> clazz)throws Exception { 
157.         String idFieldName = ""; 
158.         Field[] fields = clazz.getDeclaredFields(); 
159.         boolean flag = false; 
160.         for (Field field : fields) { 
161.             if (field.isAnnotationPresent(Id.class)) { 
162.                 idFieldName = field.getAnnotation(Id.class).value(); 
163.                 flag = true; 
164.                 break; 
165.             }  
166.         } 
167.          
168.         if (!flag) { 
169.             throw new NotFoundAnnotationException(clazz.getName() +" object not found id property."); 
170.         } 
171.          
172.         //拼装SQL 
173.         Map<String,Object> sqlWhereMap = new HashMap<String, Object>(); 
174.         sqlWhereMap.put(TABLE_ALIAS + "." + idFieldName, id); 
175.          
176.         List<T> list = findAllByConditions(sqlWhereMap, clazz); 
177.         return list.size() >0 ? list.get(0) :null; 
178.     } 
179.  
180.     @Override 
181.     public List<T> findAllByConditions(Map<String,Object> sqlWhereMap,Class<T> clazz)throws Exception { 
182.         List<T> list = new ArrayList<T>(); 
183.         String tableName = getTableName(clazz); 
184.         String idFieldName = ""; 
185.         //存储所有字段的信息 
186.         //通过反射获得要查询的字段 
187.         StringBuffer fieldNames = new StringBuffer(); 
188.         Field[] fields = clazz.getDeclaredFields(); 
189.         for (Field field : fields) { 
190.             String propertyName = field.getName(); 
191.             if (field.isAnnotationPresent(Id.class)) { 
192.                 idFieldName = field.getAnnotation(Id.class).value(); 
193.                 fieldNames.append(TABLE_ALIAS + "." + idFieldName) 
194.                           .append(" as ").append(propertyName).append(","); 
195.             } else if (field.isAnnotationPresent(Column.class)) { 
196.                 fieldNames.append(TABLE_ALIAS + "." + field.getAnnotation(Column.class).value()) 
197.                           .append(" as ").append(propertyName).append(","); 
198.             } 
199.         } 
200.         fieldNames.deleteCharAt(fieldNames.length()-1); 
201.          
202.         //拼装SQL 
203.         String sql = "select " + fieldNames +" from " + tableName + " " + TABLE_ALIAS; 
204.         PreparedStatement ps = null; 
205.         List<Object> values = null; 
206.         if (sqlWhereMap != null) { 
207.             List<Object> sqlWhereWithValues = getSqlWhereWithValues(sqlWhereMap); 
208.             if (sqlWhereWithValues !=null) { 
209.                 //拼接SQL条件 
210.                 String sqlWhere = (String)sqlWhereWithValues.get(0); 
211.                 sql += sqlWhere; 
212.                 //得到SQL条件中占位符的值 
213.                 values = (List<Object>) sqlWhereWithValues.get(1); 
214.             } 
215.         }  
216.          
217.         //设置参数占位符的值 
218.         if (values != null) { 
219.             ps = JdbcDaoHelper.getConnection().prepareStatement(sql); 
220.             setParameter(values, ps, true); 
221.         } else { 
222.             ps = JdbcDaoHelper.getConnection().prepareStatement(sql); 
223.         } 
224.          
225.          
226.         //执行SQL 
227.         ResultSet rs = ps.executeQuery(); 
228.         while(rs.next()) { 
229.             T t = clazz.newInstance(); 
230.             initObject(t, fields, rs); 
231.             list.add(t); 
232.         } 
233.          
234.         //释放资源 
235.         JdbcDaoHelper.release(ps, rs); 
236.          
237.         System.out.println(sql); 
238.         return list; 
239.     } 
240.      
241.     /**
242.      * 根据结果集初始化对象
243.      */ 
244.     private void initObject(T t, Field[] fields, ResultSet rs) 
245.             throws SQLException, IntrospectionException, 
246.             IllegalAccessException, InvocationTargetException { 
247.         for (Field field : fields) { 
248.             String propertyName = field.getName(); 
249.             Object paramVal = null; 
250.             Class<?> clazzField = field.getType(); 
251.             if (clazzField == String.class) { 
252.                 paramVal = rs.getString(propertyName); 
253.             } else if (clazzField == short.class || clazzField == Short.class) { 
254.                 paramVal = rs.getShort(propertyName); 
255.             } else if (clazzField == int.class || clazzField == Integer.class) { 
256.                 paramVal = rs.getInt(propertyName); 
257.             } else if (clazzField == long.class || clazzField == Long.class) { 
258.                 paramVal = rs.getLong(propertyName); 
259.             } else if (clazzField == float.class || clazzField == Float.class) { 
260.                 paramVal = rs.getFloat(propertyName); 
261.             } else if (clazzField == double.class || clazzField == Double.class) { 
262.                 paramVal = rs.getDouble(propertyName); 
263.             } else if (clazzField == boolean.class || clazzField == Boolean.class) { 
264.                 paramVal = rs.getBoolean(propertyName); 
265.             } else if (clazzField == byte.class || clazzField == Byte.class) { 
266.                 paramVal = rs.getByte(propertyName); 
267.             } else if (clazzField == char.class || clazzField == Character.class) { 
268.                 paramVal = rs.getCharacterStream(propertyName); 
269.             } else if (clazzField == Date.class) { 
270.                 paramVal = rs.getTimestamp(propertyName); 
271.             } else if (clazzField.isArray()) { 
272.                 paramVal = rs.getString(propertyName).split(",");  //以逗号分隔的字符串 
273.             }  
274.             PropertyDescriptor pd = new PropertyDescriptor(propertyName,t.getClass()); 
275.             pd.getWriteMethod().invoke(t, paramVal); 
276.         } 
277.     } 
278.      
279.     /**
280.      * 根据条件，返回sql条件和条件中占位符的值
281.      * @param sqlWhereMap key：字段名 value：字段值
282.      * @return 第一个元素为SQL条件，第二个元素为SQL条件中占位符的值
283.      */ 
284.     private List<Object> getSqlWhereWithValues(Map<String,Object> sqlWhereMap) { 
285.         if (sqlWhereMap.size() <1 )return null; 
286.         List<Object> list = new ArrayList<Object>(); 
287.         List<Object> fieldValues = new ArrayList<Object>(); 
288.         StringBuffer sqlWhere = new StringBuffer(" where "); 
289.         Set<Entry<String, Object>> entrySets = sqlWhereMap.entrySet(); 
290.         for (Iterator<Entry<String, Object>> iteraotr = entrySets.iterator();iteraotr.hasNext();) { 
291.             Entry<String, Object> entrySet = iteraotr.next(); 
292.             fieldValues.add(entrySet.getValue()); 
293.             Object value = entrySet.getValue(); 
294.             if (value.getClass() == String.class) { 
295.                 sqlWhere.append(entrySet.getKey()).append(" like ").append("?").append(" and "); 
296.             } else { 
297.                 sqlWhere.append(entrySet.getKey()).append("=").append("?").append(" and "); 
298.             } 
299.         } 
300.         sqlWhere.delete(sqlWhere.lastIndexOf("and"), sqlWhere.length()); 
301.         list.add(sqlWhere.toString()); 
302.         list.add(fieldValues); 
303.         return list; 
304.     } 
305.      
306.      
307.     /**
308.      * 获得表名
309.      */ 
310.     private String getTableName(Class<?> clazz)throws NotFoundAnnotationException { 
311.         if (clazz.isAnnotationPresent(Entity.class)) { 
312.             Entity entity = clazz.getAnnotation(Entity.class); 
313.             return entity.value(); 
314.         } else { 
315.             throw new NotFoundAnnotationException(clazz.getName() +" is not Entity Annotation."); 
316.         } 
317.     } 
318.      
319.     /**
320.      * 设置SQL参数占位符的值
321.      */ 
322.     private void setParameter(List<Object> values, PreparedStatement ps,boolean isSearch) 
323.             throws SQLException { 
324.         for (int i =1; i <= values.size(); i++) { 
325.             Object fieldValue = values.get(i-1); 
326.             Class<?> clazzValue = fieldValue.getClass(); 
327.             if (clazzValue == String.class) { 
328.                 if (isSearch)  
329.                     ps.setString(i, "%" + (String)fieldValue +"%"); 
330.                 else 
331.                     ps.setString(i,(String)fieldValue); 
332.                      
333.             } else if (clazzValue == boolean.class || clazzValue == Boolean.class) { 
334.                 ps.setBoolean(i, (Boolean)fieldValue); 
335.             } else if (clazzValue == byte.class || clazzValue == Byte.class) { 
336.                 ps.setByte(i, (Byte)fieldValue); 
337.             } else if (clazzValue == char.class || clazzValue == Character.class) { 
338.                 ps.setObject(i, fieldValue,Types.CHAR); 
339.             } else if (clazzValue == Date.class) { 
340.                 ps.setTimestamp(i, new Timestamp(((Date) fieldValue).getTime())); 
341.             } else if (clazzValue.isArray()) { 
342.                 Object[] arrayValue = (Object[]) fieldValue; 
343.                 StringBuffer sb = new StringBuffer(); 
344.                 for (int j =0; j < arrayValue.length; j++) { 
345.                     sb.append(arrayValue[j]).append("、"); 
346.                 } 
347.                 ps.setString(i, sb.deleteCharAt(sb.length()-1).toString()); 
348.             } else { 
349.                 ps.setObject(i, fieldValue, Types.NUMERIC); 
350.             } 
351.         } 
352.     } 
353. } 

package dao;import java.beans.IntrospectionException;import java.beans.PropertyDescriptor;import java.lang.reflect.Field;import java.lang.reflect.InvocationTargetException;import java.sql.PreparedStatement;import java.sql.ResultSet;import java.sql.SQLException;import java.sql.Timestamp;import java.sql.Types;import java.util.ArrayList;import java.util.Date;import java.util.HashMap;import java.util.Iterator;import java.util.List;import java.util.Map;import java.util.Set;import java.util.Map.Entry;import annotation.Column;import annotation.Entity;import annotation.Id;import exception.NotFoundAnnotationException;/** * 泛型DAO的JDBC实现 * @author 杨信 * @version 1.0 */public class JdbcGenericDaoImpl<T> implements GenericDao<T> {//表的别名private static final String TABLE_ALIAS = "t";@Overridepublic void save(T t) throws Exception {Class<?> clazz = t.getClass();//获得表名String tableName = getTableName(clazz);//获得字段StringBuilder fieldNames = new StringBuilder();//字段名List<Object> fieldValues = new ArrayList<Object>();//字段值StringBuilder placeholders = new StringBuilder();//占位符Field[] fields = clazz.getDeclaredFields();for (Field field : fields) {PropertyDescriptor pd = new PropertyDescriptor(field.getName(),t.getClass());if (field.isAnnotationPresent(Id.class)) {fieldNames.append(field.getAnnotation(Id.class).value()).append(",");fieldValues.add(pd.getReadMethod().invoke(t));} else if(field.isAnnotationPresent(Column.class)) {fieldNames.append(field.getAnnotation(Column.class).value()).append(",");fieldValues.add(pd.getReadMethod().invoke(t));}placeholders.append("?").append(",");}//删除最后一个逗号fieldNames.deleteCharAt(fieldNames.length()-1);placeholders.deleteCharAt(placeholders.length()-1);//拼接sqlStringBuilder sql = new StringBuilder("");sql.append("insert into ").append(tableName)   .append(" (").append(fieldNames.toString())   .append(") values (").append(placeholders).append(")") ;PreparedStatement ps = JdbcDaoHelper.getConnection().prepareStatement(sql.toString());//设置SQL参数占位符的值setParameter(fieldValues, ps, false);//执行SQLps.execute();JdbcDaoHelper.release(ps, null);System.out.println(sql + "\n" + clazz.getSimpleName() + "添加成功!");}@Overridepublic void delete(Object id,Class<T> clazz) throws Exception {//获得表名String tableName = getTableName(clazz);//获得ID字段名和值String idFieldName = "";boolean flag = false;Field[] fields = clazz.getDeclaredFields();for (Field field : fields) {if(field.isAnnotationPresent(Id.class)) {idFieldName = field.getAnnotation(Id.class).value();flag = true;break;}}if (!flag) {throw new NotFoundAnnotationException(clazz.getName() + " object not found id property.");}//拼装sqlString sql = "delete from " + tableName + " where " + idFieldName + "=?";PreparedStatement ps = JdbcDaoHelper.getConnection().prepareStatement(sql);ps.setObject(1, id);//执行SQLps.execute();JdbcDaoHelper.release(ps,null);System.out.println(sql + "\n" + clazz.getSimpleName() + "删除成功!");}@Overridepublic void update(T t) throws Exception {Class<?> clazz = t.getClass();//获得表名String tableName = getTableName(clazz);//获得字段List<Object> fieldNames = new ArrayList<Object>();//字段名List<Object> fieldValues = new ArrayList<Object>();//字段值List<String> placeholders = new ArrayList<String>();//占位符String idFieldName = "";Object idFieldValue = "";Field[] fields = clazz.getDeclaredFields();for (Field field : fields) {PropertyDescriptor pd = new PropertyDescriptor(field.getName(),t.getClass());if (field.isAnnotationPresent(Id.class)) {idFieldName = field.getAnnotation(Id.class).value();idFieldValue = pd.getReadMethod().invoke(t);} else if(field.isAnnotationPresent(Column.class)) {fieldNames.add(field.getAnnotation(Column.class).value());fieldValues.add(pd.getReadMethod().invoke(t));placeholders.add("?");}}//ID作为更新条件，放在集合中的最后一个元素fieldNames.add(idFieldName);fieldValues.add(idFieldValue);placeholders.add("?");//拼接sqlStringBuilder sql = new StringBuilder("");sql.append("update ").append(tableName).append(" set ");int index = fieldNames.size() - 1;for (int i = 0; i < index; i++) {sql.append(fieldNames.get(i)).append("=").append(placeholders.get(i)).append(",");}sql.deleteCharAt(sql.length()-1).append(" where ").append(fieldNames.get(index)).append("=").append("?");//设置SQL参数占位符的值PreparedStatement ps = JdbcDaoHelper.getConnection().prepareStatement(sql.toString());setParameter(fieldValues, ps, false);//执行SQLps.execute();JdbcDaoHelper.release(ps, null);System.out.println(sql + "\n" + clazz.getSimpleName() + "修改成功.");}@Overridepublic T get(Object id,Class<T> clazz) throws Exception {String idFieldName = "";Field[] fields = clazz.getDeclaredFields();boolean flag = false;for (Field field : fields) {if (field.isAnnotationPresent(Id.class)) {idFieldName = field.getAnnotation(Id.class).value();flag = true;break;} }if (!flag) {throw new NotFoundAnnotationException(clazz.getName() + " object not found id property.");}//拼装SQLMap<String,Object> sqlWhereMap = new HashMap<String, Object>();sqlWhereMap.put(TABLE_ALIAS + "." + idFieldName, id);List<T> list = findAllByConditions(sqlWhereMap, clazz);return list.size() > 0 ? list.get(0) : null;}@Overridepublic List<T> findAllByConditions(Map<String,Object> sqlWhereMap,Class<T> clazz) throws Exception {List<T> list = new ArrayList<T>();String tableName = getTableName(clazz);String idFieldName = "";//存储所有字段的信息//通过反射获得要查询的字段StringBuffer fieldNames = new StringBuffer();Field[] fields = clazz.getDeclaredFields();for (Field field : fields) {String propertyName = field.getName();if (field.isAnnotationPresent(Id.class)) {idFieldName = field.getAnnotation(Id.class).value();fieldNames.append(TABLE_ALIAS + "." + idFieldName)  .append(" as ").append(propertyName).append(",");} else if (field.isAnnotationPresent(Column.class)) {fieldNames.append(TABLE_ALIAS + "." + field.getAnnotation(Column.class).value())  .append(" as ").append(propertyName).append(",");}}fieldNames.deleteCharAt(fieldNames.length()-1);//拼装SQLString sql = "select " + fieldNames + " from " + tableName + " " + TABLE_ALIAS;PreparedStatement ps = null;List<Object> values = null;if (sqlWhereMap != null) {List<Object> sqlWhereWithValues = getSqlWhereWithValues(sqlWhereMap);if (sqlWhereWithValues != null) {//拼接SQL条件String sqlWhere = (String)sqlWhereWithValues.get(0);sql += sqlWhere;//得到SQL条件中占位符的值values = (List<Object>) sqlWhereWithValues.get(1);}} //设置参数占位符的值if (values != null) {ps = JdbcDaoHelper.getConnection().prepareStatement(sql);setParameter(values, ps, true);} else {ps = JdbcDaoHelper.getConnection().prepareStatement(sql);}//执行SQLResultSet rs = ps.executeQuery();while(rs.next()) {T t = clazz.newInstance();initObject(t, fields, rs);list.add(t);}//释放资源JdbcDaoHelper.release(ps, rs);System.out.println(sql);return list;}/** * 根据结果集初始化对象 */private void initObject(T t, Field[] fields, ResultSet rs)throws SQLException, IntrospectionException,IllegalAccessException, InvocationTargetException {for (Field field : fields) {String propertyName = field.getName();Object paramVal = null;Class<?> clazzField = field.getType();if (clazzField == String.class) {paramVal = rs.getString(propertyName);} else if (clazzField == short.class || clazzField == Short.class) {paramVal = rs.getShort(propertyName);} else if (clazzField == int.class || clazzField == Integer.class) {paramVal = rs.getInt(propertyName);} else if (clazzField == long.class || clazzField == Long.class) {paramVal = rs.getLong(propertyName);} else if (clazzField == float.class || clazzField == Float.class) {paramVal = rs.getFloat(propertyName);} else if (clazzField == double.class || clazzField == Double.class) {paramVal = rs.getDouble(propertyName);} else if (clazzField == boolean.class || clazzField == Boolean.class) {paramVal = rs.getBoolean(propertyName);} else if (clazzField == byte.class || clazzField == Byte.class) {paramVal = rs.getByte(propertyName);} else if (clazzField == char.class || clazzField == Character.class) {paramVal = rs.getCharacterStream(propertyName);} else if (clazzField == Date.class) {paramVal = rs.getTimestamp(propertyName);} else if (clazzField.isArray()) {paramVal = rs.getString(propertyName).split(",");//以逗号分隔的字符串} PropertyDescriptor pd = new PropertyDescriptor(propertyName,t.getClass());pd.getWriteMethod().invoke(t, paramVal);}}/** * 根据条件，返回sql条件和条件中占位符的值 * @param sqlWhereMap key：字段名 value：字段值 * @return 第一个元素为SQL条件，第二个元素为SQL条件中占位符的值 */private List<Object> getSqlWhereWithValues(Map<String,Object> sqlWhereMap) {if (sqlWhereMap.size() <1 ) return null;List<Object> list = new ArrayList<Object>();List<Object> fieldValues = new ArrayList<Object>();StringBuffer sqlWhere = new StringBuffer(" where ");Set<Entry<String, Object>> entrySets = sqlWhereMap.entrySet();for (Iterator<Entry<String, Object>> iteraotr = entrySets.iterator();iteraotr.hasNext();) {Entry<String, Object> entrySet = iteraotr.next();fieldValues.add(entrySet.getValue());Object value = entrySet.getValue();if (value.getClass() == String.class) {sqlWhere.append(entrySet.getKey()).append(" like ").append("?").append(" and ");} else {sqlWhere.append(entrySet.getKey()).append("=").append("?").append(" and ");}}sqlWhere.delete(sqlWhere.lastIndexOf("and"), sqlWhere.length());list.add(sqlWhere.toString());list.add(fieldValues);return list;}/** * 获得表名 */private String getTableName(Class<?> clazz) throws NotFoundAnnotationException {if (clazz.isAnnotationPresent(Entity.class)) {Entity entity = clazz.getAnnotation(Entity.class);return entity.value();} else {throw new NotFoundAnnotationException(clazz.getName() + " is not Entity Annotation.");}}/** * 设置SQL参数占位符的值 */private void setParameter(List<Object> values, PreparedStatement ps, boolean isSearch)throws SQLException {for (int i = 1; i <= values.size(); i++) {Object fieldValue = values.get(i-1);Class<?> clazzValue = fieldValue.getClass();if (clazzValue == String.class) {if (isSearch) ps.setString(i, "%" + (String)fieldValue + "%");elseps.setString(i,(String)fieldValue);} else if (clazzValue == boolean.class || clazzValue == Boolean.class) {ps.setBoolean(i, (Boolean)fieldValue);} else if (clazzValue == byte.class || clazzValue == Byte.class) {ps.setByte(i, (Byte)fieldValue);} else if (clazzValue == char.class || clazzValue == Character.class) {ps.setObject(i, fieldValue,Types.CHAR);} else if (clazzValue == Date.class) {ps.setTimestamp(i, new Timestamp(((Date) fieldValue).getTime()));} else if (clazzValue.isArray()) {Object[] arrayValue = (Object[]) fieldValue;StringBuffer sb = new StringBuffer();for (int j = 0; j < arrayValue.length; j++) {sb.append(arrayValue[j]).append("、");}ps.setString(i, sb.deleteCharAt(sb.length()-1).toString());} else {ps.setObject(i, fieldValue, Types.NUMERIC);}}}}

 

4、定义三个注解Entity、Id、Column，生命周期保存在运行期间，以便通过反射获取

1）、Entity

 

[java] view plaincopyprint?

1. package annotation; 
2.  
3. import java.lang.annotation.ElementType; 
4. import java.lang.annotation.Retention; 
5. import java.lang.annotation.RetentionPolicy; 
6. import java.lang.annotation.Target; 
7.  
8. /**
9. * 数据库表的的名称
10. */ 
11. @Retention(RetentionPolicy.RUNTIME) 
12. @Target(ElementType.TYPE) 
13. public @interface Entity { 
14.  
15.     /**
16.      * 表名
17.      */ 
18.     String value(); 
19.      
20. } 

package annotation;import java.lang.annotation.ElementType;import java.lang.annotation.Retention;import java.lang.annotation.RetentionPolicy;import java.lang.annotation.Target;/** * 数据库表的的名称 */@Retention(RetentionPolicy.RUNTIME)@Target(ElementType.TYPE)public @interface Entity {/** * 表名 */String value();}

2）、Id

[java] view plaincopyprint?

1. package annotation; 
2.  
3. import java.lang.annotation.ElementType; 
4. import java.lang.annotation.Retention; 
5. import java.lang.annotation.RetentionPolicy; 
6. import java.lang.annotation.Target; 
7.  
8. /**
9. * 标识数据库字段的ID
10. */ 
11. @Retention(RetentionPolicy.RUNTIME) 
12. @Target(ElementType.FIELD) 
13. public @interface Id { 
14.  
15.     /**
16.      * ID的名称
17.      * @return
18.      */ 
19.     String value(); 
20.      
21. } 

package annotation;import java.lang.annotation.ElementType;import java.lang.annotation.Retention;import java.lang.annotation.RetentionPolicy;import java.lang.annotation.Target;/** * 标识数据库字段的ID */@Retention(RetentionPolicy.RUNTIME)@Target(ElementType.FIELD)public @interface Id {/** * ID的名称 * @return */String value();}

3）、Column

[java] view plaincopyprint?

1. package annotation; 
2.  
3. import java.lang.annotation.ElementType; 
4. import java.lang.annotation.Retention; 
5. import java.lang.annotation.RetentionPolicy; 
6. import java.lang.annotation.Target; 
7.  
8. /**
9. * 标识数据库字段的名称
10. * @author 杨信
11. *
12. */ 
13. @Retention(RetentionPolicy.RUNTIME) 
14. @Target(ElementType.FIELD) 
15. public @interface Column { 
16.      
17.     /**
18.      * 字段名称
19.      */ 
20.     String value(); 
21.      
22.     /**
23.      * 字段的类型
24.      * @return
25.      */ 
26.     Class<?> type() default String.class; 
27.      
28.     /**
29.      * 字段的长度
30.      * @return
31.      */ 
32.     int length() default0; 
33.  
34. } 

package annotation;import java.lang.annotation.ElementType;import java.lang.annotation.Retention;import java.lang.annotation.RetentionPolicy;import java.lang.annotation.Target;/** * 标识数据库字段的名称 * @author 杨信 * */@Retention(RetentionPolicy.RUNTIME)@Target(ElementType.FIELD)public @interface Column {/** * 字段名称 */String value();/** * 字段的类型 * @return */Class<?> type() default String.class;/** * 字段的长度 * @return */int length() default 0;}

五、定义一个JavaBean，用于测试使用

要求：

1）、类名必须用Entity注解标识，并指定数据库中对应的表名

2）、Id属性必须用Id注解标识，并指定表中所对应的字段名

3）、其它属性必须用Column注解标识，并指定表中所对应的字段名

4）、JavaBean属性的数据类型目前只实现了8大基本数据类型、String和这些基本类型的数组类型。

5）、JavaBean属性目前没有做字段的长度与类型的判断，待以后改进。

[java] view plaincopyprint?

1. package model; 
2.  
3. import java.util.Date; 
4.  
5. import annotation.Column; 
6. import annotation.Entity; 
7. import annotation.Id; 
8.  
9. /**
10. * 图书
11. */ 
12. @Entity("t_book")  //表名 
13. public class Book { 
14.  
15.     /**
16.      * 图书编号
17.      */ 
18.     @Id("t_isbn") 
19.     private String isbn; 
20.  
21.     /**
22.      * 书名
23.      */ 
24.     @Column("t_name") 
25.     private String name; 
26.  
27.     /**
28.      * 作者
29.      */ 
30.     @Column("t_author") 
31.     private String author; 
32.  
33.     /**
34.      * 出版社
35.      */ 
36.     @Column("t_publishing") 
37.     private String publishing; 
38.  
39.     /**
40.      * 出版时间
41.      */ 
42.     @Column(value = "t_pubdate") 
43.     private Date pubdate; 
44.  
45.     /**
46.      * 价格
47.      */ 
48.     @Column(value = "t_price") 
49.     private double price; 
50.  
51.     public String getIsbn() { 
52.         return isbn; 
53.     } 
54.  
55.     public void setIsbn(String isbn) { 
56.         this.isbn = isbn; 
57.     } 
58.  
59.     public String getName() { 
60.         return name; 
61.     } 
62.  
63.     public void setName(String name) { 
64.         this.name = name; 
65.     } 
66.  
67.     public String getAuthor() { 
68.         return author; 
69.     } 
70.  
71.     public void setAuthor(String author) { 
72.         this.author = author; 
73.     } 
74.  
75.     public String getPublishing() { 
76.         return publishing; 
77.     } 
78.  
79.     public void setPublishing(String publishing) { 
80.         this.publishing = publishing; 
81.     } 
82.  
83.     public Date getPubdate() { 
84.         return pubdate; 
85.     } 
86.  
87.     public void setPubdate(Date pubdate) { 
88.         this.pubdate = pubdate; 
89.     } 
90.  
91.     public double getPrice() { 
92.         return price; 
93.     } 
94.  
95.     public void setPrice(double price) { 
96.         this.price = price; 
97.     } 
98.  
99.     @Override 
100.     public String toString() { 
101.         return "书名: " + name +" 图书编号: " + isbn + " 作者: " + author 
102.                 + " 出版社: " + publishing +" 出版时间: " + pubdate 
103.                 + " 价格: " + price; 
104.     } 
105. } 

package model;import java.util.Date;import annotation.Column;import annotation.Entity;import annotation.Id;/** * 图书 */@Entity("t_book")//表名public class Book {/** * 图书编号 */@Id("t_isbn")private String isbn;/** * 书名 */@Column("t_name")private String name;/** * 作者 */@Column("t_author")private String author;/** * 出版社 */@Column("t_publishing")private String publishing;/** * 出版时间 */@Column(value = "t_pubdate")private Date pubdate;/** * 价格 */@Column(value = "t_price")private double price;public String getIsbn() {return isbn;}public void setIsbn(String isbn) {this.isbn = isbn;}public String getName() {return name;}public void setName(String name) {this.name = name;}public String getAuthor() {return author;}public void setAuthor(String author) {this.author = author;}public String getPublishing() {return publishing;}public void setPublishing(String publishing) {this.publishing = publishing;}public Date getPubdate() {return pubdate;}public void setPubdate(Date pubdate) {this.pubdate = pubdate;}public double getPrice() {return price;}public void setPrice(double price) {this.price = price;}@Overridepublic String toString() {return "书名: " + name + " 图书编号: " + isbn + " 作者: " + author+ " 出版社: " + publishing + " 出版时间: " + pubdate+ " 价格: " + price;}}

六、使用Junit4进行单元测试

[java] view plaincopyprint?

1. package xml; 
2.  
3. import java.io.InputStream; 
4. import java.util.HashMap; 
5. import java.util.List; 
6. import java.util.Map; 
7.  
8. import model.Book; 
9.  
10. import org.junit.BeforeClass; 
11. import org.junit.Test; 
12.  
13. import util.DateUtils; 
14. import dao.GenericDao; 
15. import dao.JdbcGenericDaoImpl; 
16.  
17. /**
18. * 测试泛型DAO的CRUD操作
19. */ 
20. public class GenericDaoTest { 
21.      
22.     private GenericDao<Book> bookDao =new JdbcGenericDaoImpl<Book>(); 
23.      
24.     private static InputStream is; 
25.  
26.     @BeforeClass 
27.     public staticvoid setUpBeforeClass() throws Exception { 
28.         is = XmlParserTest.class.getResourceAsStream("/books.xml"); 
29.     } 
30.      
31.     @Test 
32.     public void testSave()throws Exception { 
33.         List<Book> books = SaxHelper.saxReader(is); 
34.         for (Book book : books) { 
35.             bookDao.save(book); 
36.         } 
37.     } 
38.      
39.     @Test 
40.     public void testStudentFindAll1()throws Exception { 
41.         System.out.println("\n-------------更新、删除前,测试查询所有记录--------------------"); 
42.         List<Book> books = bookDao.findAllByConditions(null, Book.class); 
43.         for (Book book : books) { 
44.             System.out.println(book); 
45.         } 
46.     }  
47.      
48.     @Test 
49.     public void testDelete()throws Exception { 
50.         System.out.println("\n-------------测试删除一条记录--------------------"); 
51.         bookDao.delete("9787111349662",Book.class); 
52.     } 
53.      
54.     @Test 
55.     public void testGet()throws Exception { 
56.         System.out.println("\n-------------测试查询一条记录--------------------"); 
57.         Book book = bookDao.get("9787121025389", Book.class); 
58.         System.out.println(book); 
59.     } 
60.      
61.     @Test 
62.     public void testUpdate()throws Exception { 
63.         System.out.println("\n-------------测试修改一条记录--------------------"); 
64.         Book book = new Book(); 
65.         book.setIsbn("9787121025389"); 
66.         book.setName("JAVA面向对象编程"); 
67.         book.setAuthor("孙卫琴"); 
68.         book.setPublishing("电子工业出版社"); 
69.         book.setPubdate(DateUtils.string2Date("yyyy-MM-dd","2006-07-01")); 
70.         book.setPrice(50.6); 
71.         bookDao.update(book); 
72.     } 
73.      
74.     @Test 
75.     public void testStudentFindAll2()throws Exception { 
76.         System.out.println("\n-------------更新、删除前,测试根据条件查询所有记录--------------------"); 
77.         Map<String,Object> sqlWhereMap = new HashMap<String, Object>(); 
78.         //sqlWhereMap.put("t_isbn", "9787111213826"); 
79.         //sqlWhereMap.put("t_name", "Java"); 
80.         sqlWhereMap.put("t_publishing","机械工业出版社"); 
81.         //sqlWhereMap.put("t_pubdate", new Date(new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").parse("2007-01-01 12:06:00").getTime())); 
82.         List<Book> books = bookDao.findAllByConditions(null, Book.class); 
83.         for (Book book : books) { 
84.             System.out.println(book); 
85.         } 
86.     }  
87.  
88. } 

package xml;import java.io.InputStream;import java.util.HashMap;import java.util.List;import java.util.Map;import model.Book;import org.junit.BeforeClass;import org.junit.Test;import util.DateUtils;import dao.GenericDao;import dao.JdbcGenericDaoImpl;/** * 测试泛型DAO的CRUD操作 */public class GenericDaoTest {private GenericDao<Book> bookDao = new JdbcGenericDaoImpl<Book>();private static InputStream is;@BeforeClasspublic static void setUpBeforeClass() throws Exception {is = XmlParserTest.class.getResourceAsStream("/books.xml");}@Testpublic void testSave() throws Exception {List<Book> books = SaxHelper.saxReader(is);for (Book book : books) {bookDao.save(book);}}@Testpublic void testStudentFindAll1() throws Exception {System.out.println("\n-------------更新、删除前,测试查询所有记录--------------------");List<Book> books = bookDao.findAllByConditions(null, Book.class);for (Book book : books) {System.out.println(book);}} @Testpublic void testDelete() throws Exception {System.out.println("\n-------------测试删除一条记录--------------------");bookDao.delete("9787111349662",Book.class);}@Testpublic void testGet() throws Exception {System.out.println("\n-------------测试查询一条记录--------------------");Book book = bookDao.get("9787121025389", Book.class);System.out.println(book);}@Testpublic void testUpdate() throws Exception {System.out.println("\n-------------测试修改一条记录--------------------");Book book = new Book();book.setIsbn("9787121025389");book.setName("JAVA面向对象编程");book.setAuthor("孙卫琴");book.setPublishing("电子工业出版社");book.setPubdate(DateUtils.string2Date("yyyy-MM-dd", "2006-07-01"));book.setPrice(50.6);bookDao.update(book);}@Testpublic void testStudentFindAll2() throws Exception {System.out.println("\n-------------更新、删除前,测试根据条件查询所有记录--------------------");Map<String,Object> sqlWhereMap = new HashMap<String, Object>();//sqlWhereMap.put("t_isbn", "9787111213826");//sqlWhereMap.put("t_name", "Java");sqlWhereMap.put("t_publishing", "机械工业出版社");//sqlWhereMap.put("t_pubdate", new Date(new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").parse("2007-01-01 12:06:00").getTime()));List<Book> books = bookDao.findAllByConditions(null, Book.class);for (Book book : books) {System.out.println(book);}} }

七、测试结果