从数据库读取数据后利用反射为对应的实体类的属性赋值

1、连接数据库并关闭连接（jdbctools.java）

package com.xiaojie.dao;

import java.io.IOException;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

import javax.sql.DataSource;

import com.mchange.v2.c3p0.ComboPooledDataSource;

public class Jdbctools {
private static DataSource ds=null;
//数据库连接池应只被初始化一次
static{
ds=new ComboPooledDataSource("helloc3p0");
}
//获取数据库连接
public static  Connection getConnection() throws ClassNotFoundException, SQLException, IOException{
return ds.getConnection();
}
public static void shifanglianjie(Connection ct, PreparedStatement ps,ResultSet rs) {
if(rs!=null){
try {
rs.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
if(ps!=null){
try {
ps.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
if(ct!=null){
try {
ct.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}

}

2、DAO 模块

package com.xiaojie.dao;
import java.io.IOException;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.Date;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import com.xiaojie.beans.Trade;

import java.sql.SQLException;
public class DAO<T> {
//查询一条记录，返回对应的对象
public <T> T query(Class<T> clazz,String sql,Object...args){
T example=null;
Connection ct=null;
PreparedStatement ps=null;
ResultSet rs=null;
try {
//1、获取connection
ct=Jdbctools.getConnection();
System.out.println("query获取到数据库的连接了");
//2、获取PreparedStatement
ps=ct.prepareStatement(sql);
//3、填充占位符
for(int i=0;i<args.length;i++){
ps.setObject(i+1, args[i]);
}
//4、进行查询，得到ResultSet
rs=ps.executeQuery();
//5、准备一个Map<String,Object>:(前提是结果集中要有记录)
if(rs.next()){
Map<String,Object> values=new HashMap<String,Object>();

//6、得到ResultSetMetaData对象
ResultSetMetaData rsd=rs.getMetaData();
//7、处理ResultSet,把指针向下移动一个单位

//8、由ResultSetMetaData对象得到结果集中有多少列
int lieshu=rsd.getColumnCount();
//9、由ResultSetMetaData对象得到每一列的别名，由ResultSet得到具体每一列的值
for(int i=0;i<lieshu;i++){
String lieming=rsd.getColumnLabel(i+1);
Object liezhi=rs.getObject(i+1);
//10、填充Map对象
values.put(lieming,liezhi);
}

//11、用反射创建Class对应的对象
example=clazz.newInstance();
//12、遍历Map对象，用反射填充对象的属性值，
for(Map.Entry<String, Object> ent:values.entrySet()){
String name=ent.getKey();
Object value=ent.getValue();
//用反射赋值
ReflectionUtils.setFieldValue(example, name,  value);

}
}
} catch (Exception e) {
e.printStackTrace();
}finally{
Jdbctools.shifanglianjie(ct, ps, rs);
}
return example;

}
//查询多条记录，返回多个对应的对象
public List<T>  querylist(Class<T> clazz,String sql,Object...args){
T example=null;
Connection ct=null;
PreparedStatement ps=null;
ResultSet rs=null;
List li=new ArrayList();
try {
//1、获取connection
ct=Jdbctools.getConnection();
System.out.println("querylist获取到数据库的连接了");
//2、获取PreparedStatement
ps=ct.prepareStatement(sql);
//3、填充占位符
for(int i=0;i<args.length;i++){
ps.setObject(i+1, args[i]);
}
//4、进行查询，得到ResultSet
rs=ps.executeQuery();
//5、准备一个Map<String,Object>:(前提是结果集中要有记录)

while(rs.next()){
Map<String,Object> values=new HashMap<String,Object>();

//6、得到ResultSetMetaData对象
ResultSetMetaData rsd=rs.getMetaData();
//7、处理ResultSet,把指针向下移动一个单位

//8、由ResultSetMetaData对象得到结果集中有多少列
int lieshu=rsd.getColumnCount();
//9、由ResultSetMetaData对象得到每一列的别名，由ResultSet得到具体每一列的值
for(int i=0;i<lieshu;i++){
String lieming=rsd.getColumnLabel(i+1);
Object liezhi=rs.getObject(i+1);
//10、填充Map对象
values.put(lieming,liezhi);
}

//11、用反射创建Class对应的对象
example=clazz.newInstance();
//12、遍历Map对象，用反射填充对象的属性值，
for(Map.Entry<String, Object> ent:values.entrySet()){
String name=ent.getKey();
Object value=ent.getValue();
//用反射赋值
ReflectionUtils.setFieldValue(example, name,  value);

}
li.add(example);
}
} catch (Exception e) {
e.printStackTrace();
}finally{
Jdbctools.shifanglianjie(ct, ps, rs);
}
return li;

}
}

3、反射工具类

package com.xiaojie.dao;

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 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 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;
}
}

4、数据库对应的那个Javabeans实体类

package com.xiaojie.beans;

import java.util.Date;

public class Trade {
private int tradeid;
private int userid;
private Date tradetime;
public int getTradeid() {
return tradeid;
}
public void setTradeid(int tradeid) {
this.tradeid = tradeid;
}
public int getUserid() {
return userid;
}
public void setUserid(int userid) {
this.userid = userid;
}
public Date getTradetime() {
return tradetime;
}
public void setTradetime(Date tradetime) {
this.tradetime = tradetime;
}
public Trade(int tradeid, int userid, Date tradetime) {
super();
this.tradeid = tradeid;
this.userid = userid;
this.tradetime = tradetime;
}
public Trade() {
super();
}

}

5、写了一个测试类试一下效果（前提是该导入的jar包都导入了，而且数据库建有相应的Javabeans的表，c3p0配置文件等都弄好了）

package com.xiaojie.test;

import java.io.IOException;
import java.sql.Date;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;

import org.junit.Test;

import com.xiaojie.beans.Trade;
import com.xiaojie.dao.DAO;

public class Daotest {
private DAO dao=new DAO();
<span style="white-space:pre">	</span>//以下测试方法是测试从数据库查询一条记录给相应的Javabean的属性赋值，并在控制台显示出一条打印结果
@Test
public void testquery() throws ClassNotFoundException, SQLException, IOException{
String sql="select * from trade where tradeid=?";
Trade trade=new Trade();
trade= (Trade) dao.query(Trade.class,sql,1);
System.out.println("tradeid:"+trade.getTradeid()+"\nuserid:"+trade.getUserid()+"\ntradetiem:"+trade.getTradetime());

}
//以下测试方法是从数据库查询后的结果（不只一条记录）给相应的Javabean的属性赋值，并在控制台显示出多条打印结果
@Test
public void testquerylist(){
String sql="select * from trade";
Trade trade=new Trade();

List<Trade>trades=new ArrayList<Trade>();
trades=(List<Trade>) dao.querylist(Trade.class,sql);
for(Trade trade1:trades){

System.out.println("tradeid:"+trade1.getTradeid()+"\nuserid:"+trade1.getUserid()+"\ntradetiem:"+trade1.getTradetime());
}

}
}