利用反射及JDBC元数据编写通用的查询方法，jdbc元数据,遇到了若干问题： 1.从

利用反射及JDBC元数据编写通用的查询方法，jdbc元数据,遇到了若干问题： 1.从

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.BigDecimalat 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