JDBC：利用反射及JDBC元数据编写通用的查询方法

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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;
	}
}

JDBC：利用反射及JDBC元数据编写通用的查询方法

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原文地址：http://blog.csdn.net/wjw0130/article/details/43760487