利用反射及JDBC元数据编写通用的查询方法
遇到了若干问题：
1.从oracle返回的列名都是大写，再用反射，就找不到相对应得 名字
2.oracle 中number类型 返回来，就变成了BigDecimal
public static void main(String[] args){ String sql = "SELECT IDCARD , examcard , " + "studentname ," + "lacation LoCATION,grade " + " FROM student WHERE IDCARD = ?"; Student s = get(Student.class, sql, 7); System.out.println(s); } //String sql = "SELECT id, name, email, birth " <span style="white-space:pre"> </span>//<span style="white-space:pre"> </span>+ "FROM customers WHERE id = ?"; public static <T> T get(Class<T> clazz, String sql, Object... args) { T entity = null; Connection connection = null; PreparedStatement preparedStatement = null; ResultSet resultSet = null; try { //1. 得到 ResultSet 对象 connection = JDBC_Tools.getConnection(); preparedStatement = connection.prepareStatement(sql); for (int i = 0; i < args.length; i++) { preparedStatement.setObject(i + 1, args[i]); } resultSet = preparedStatement.executeQuery(); //2. 得到 ResultSetMetaData 对象 ResultSetMetaData rsmd = resultSet.getMetaData(); //3. 创建一个 Map<String, Object> 对象, 键: SQL 查询的列的别名, //值: 列的值 Map<String, Object> values = new HashMap<>(); //4. 处理结果集. 利用 ResultSetMetaData 填充 3 对应的 Map 对象 if(resultSet.next()){ for(int i = 0; i < rsmd.getColumnCount(); i++){ //从 ResultSetMetaData 获取列的别名 String columnLabel = rsmd.getColumnLabel(i + 1); //从 结果集 中获取列的值 Object columnValue = resultSet.getObject(i + 1); values.put(columnLabel, columnValue); } } //5. 若 Map 不为空集, 利用反射创建 clazz 对应的对象 if(values.size() > 0){ entity = clazz.newInstance(); //5. 遍历 Map 对象, 利用反射为 Class 对象的对应的属性赋值. for(Map.Entry<String, Object> entry: values.entrySet()){ String fieldName = entry.getKey(); Object value = entry.getValue(); //System.out.println(fieldName+":"+value); ReflectionUtils.setFieldValue(entity, fieldName, value); //出问题 //System.out.println(ReflectionUtils.getDeclaredField(entity,fieldName)); } } } catch (Exception e) { e.printStackTrace(); } finally { JDBC_Tools.relaseSource(resultSet, connection, preparedStatement); } return entity; } } ReflectionUtils.setFieldValue(entity, fieldName, value);出问题
java.lang.IllegalArgumentException: Can not set int field xuezaipiao3.Student.GRADE to java.math.BigDecimal
at sun.reflect.UnsafeFieldAccessorImpl.throwSetIllegalArgumentException(UnsafeFieldAccessorImpl.java:164)
at sun.reflect.UnsafeFieldAccessorImpl.throwSetIllegalArgumentException(UnsafeFieldAccessorImpl.java:168)
at sun.reflect.UnsafeIntegerFieldAccessorImpl.set(UnsafeIntegerFieldAccessorImpl.java:98)
at java.lang.reflect.Field.set(Field.java:741)
at xuezaipiao3.ReflectionUtils.setFieldValue(ReflectionUtils.java:156)
at xuezaipiao3.ThinkInJDBC.get(ThinkInJDBC.java:77)
at xuezaipiao3.ThinkInJDBC.main(ThinkInJDBC.java:45)
Student [IDCARD=0, EXAMCARD=0, STUDENTNAME=null, LOCATION=7, GRADE=0]
Oracle 中 number类型 通过ResultSet 的 getObject() 返回的是 BigDecimal ，无法强制转化，而且 ResultSetMetaData 的 getColumnLabel() 取回的 列的别名是大写
MySQL不存在这样的问题
用的 Oracle 10g
ReflectionUtils
package xuezaipiao3; import java.lang.reflect.Field; import java.lang.reflect.InvocationTargetException; import java.lang.reflect.Method; import java.lang.reflect.Modifier; import java.lang.reflect.ParameterizedType; import java.lang.reflect.Type; /** * 反射的 Utils 函数集合 * 提供访问私有变量, 获取泛型类型 Class, 提取集合中元素属性等 Utils 函数 * @author Administrator * */ public class ReflectionUtils { /** * 通过反射, 获得定义 Class 时声明的父类的泛型参数的类型 * 如: public EmployeeDao extends BaseDao<Employee, String> * @param <T> * @param clazz * @param index * @return */ @SuppressWarnings("unchecked") public static Class getSuperClassGenricType(Class clazz, int index){ Type genType = clazz.getGenericSuperclass(); if(!(genType instanceof ParameterizedType)){ return Object.class; } Type [] params = ((ParameterizedType)genType).getActualTypeArguments(); if(index >= params.length || index < 0){ return Object.class; } if(!(params[index] instanceof Class)){ return Object.class; } return (Class) params[index]; } /** * 通过反射, 获得 Class 定义中声明的父类的泛型参数类型 * 如: public EmployeeDao extends BaseDao<Employee, String> * @param <T> * @param clazz * @return */ @SuppressWarnings("unchecked") public static<T> Class<T> getSuperGenericType(Class<T> clazz){ return getSuperClassGenricType(clazz, 0); } /** * 循环向上转型, 获取对象的 DeclaredMethod * @param object * @param methodName * @param parameterTypes * @return */ public static Method getDeclaredMethod(Object object, String methodName, Class<?>[] parameterTypes){ for(Class<?> superClass = object.getClass(); superClass != Object.class; superClass = superClass.getSuperclass()){ try { //superClass.getMethod(methodName, parameterTypes); return superClass.getDeclaredMethod(methodName, parameterTypes); } catch (NoSuchMethodException e) { //Method 不在当前类定义, 继续向上转型 } //.. } return null; } /** * 使 filed 变为可访问 * @param field */ public static void makeAccessible(Field field){ if(!Modifier.isPublic(field.getModifiers())){ field.setAccessible(true); } } /** * 循环向上转型, 获取对象的 DeclaredField * @param object * @param filedName * @return */ public static Field getDeclaredField(Object object, String filedName){ for(Class<?> superClass = object.getClass(); superClass != Object.class; superClass = superClass.getSuperclass()){ try { return superClass.getDeclaredField(filedName); } catch (NoSuchFieldException e) { //Field 不在当前类定义, 继续向上转型 } } return null; } /** * 直接调用对象方法, 而忽略修饰符(private, protected) * @param object * @param methodName * @param parameterTypes * @param parameters * @return * @throws InvocationTargetException * @throws IllegalArgumentException */ public static Object invokeMethod(Object object, String methodName, Class<?> [] parameterTypes, Object [] parameters) throws InvocationTargetException{ Method method = getDeclaredMethod(object, methodName, parameterTypes); if(method == null){ throw new IllegalArgumentException("Could not find method [" + methodName + "] on target [" + object + "]"); } method.setAccessible(true); try { return method.invoke(object, parameters); } catch(IllegalAccessException e) { System.out.println("不可能抛出的异常"); } return null; } /** * 直接设置对象属性值, 忽略 private/protected 修饰符, 也不经过 setter * @param object * @param fieldName * @param value */ public static void setFieldValue(Object object, String fieldName, 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) { System.out.println("不可能抛出的异常"); } } /** * 直接读取对象的属性值, 忽略 private/protected 修饰符, 也不经过 getter * @param object * @param fieldName * @return */ public static Object getFieldValue(Object object, String fieldName){ Field field = getDeclaredField(object, fieldName); if (field == null) throw new IllegalArgumentException("Could not find field [" + fieldName + "] on target [" + object + "]"); makeAccessible(field); Object result = null; try { result = field.get(object); } catch (IllegalAccessException e) { System.out.println("不可能抛出的异常"); } return result; } } 来自：http://blog.csdn.net/wjw0130/article/details/43760487