利用反射实现mysql数据库sql查询 返回List<E>泛型（持久化）对象

利用反射实现sql查询，得到持久化对象

标题想不出言简意赅的词汇，想找相关信息的朋友们，先来看看方法结构是否符合你的胃口。

public static <E> List<E> getObjectBySql(String sql,E e)
{
List<E> list = new ArrayList<E>();
//...
//.方法区域
//...
return list;
}

正题

重温了一下hibernate中的hql，发现其中得到持久化对象很新奇，自己研究了会儿。

实现原理是利用 反射机制 通过 传入的Class对象（类似String.Class） 得到该对象的所有方法、变量名。

实现步骤如下：

import org.apache.commons.dbcp.BasicDataSourceFactory;
import javax.sql.DataSource;
import java.io.FileInputStream;
import java.io.IOException;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.sql.*;
import java.util.ArrayList;
import java.util.List;
import java.util.Properties;

/**
* Created by HaoWeiTao on 2017/5/15.
*/
public class Eazy01 {
private static DataSource ds ;//连接池

static {
Properties properties = new Properties();//得到一个properties对象
try {
properties.load(new FileInputStream("src\\main\\dbcp.properties"));//加载properties文件
ds = BasicDataSourceFactory.createDataSource(properties);//通过连接池工厂加载数据
} catch (IOException e) {
e.printStackTrace();
} catch (Exception e) {
e.printStackTrace();
}
}
public static <E> List<E> getObjectBySql(String sql,E e)
{
Connection conn = null;     //连接
Statement st = null;
ResultSet rs = null;
List<E> list = new ArrayList<E>();
try {
conn = ds.getConnection();  //得到一个连接
st = conn.createStatement();
rs = st.executeQuery(sql);
ResultSetMetaData rsmd = rs.getMetaData();//得到结果集元数据对象，可以通过该对象得到列数，列名等信息
int count = 0;
while (rs.next())
{
Class<?> eClas = e.getClass();
E eObj = (E) eClas.newInstance();
int len = rsmd.getColumnCount();
count++;
for (int i=1;i<=len;i++)
{
//得到列名
String columnName = rsmd.getColumnName(i);
//将列名首字母转大写
String columnNameUpCase = columnName.substring(0,1).toUpperCase()+columnName.substring(1);
//得到每一列在泛型对象中对应的set方法名
String columnSetMethod = "set"+columnNameUpCase;
Field filed = eClas.getDeclaredField(columnName);
Class<?> clazz = filed.getType();   //得到字段名对应的类型
//字段为int类型
if (clazz.isAssignableFrom(int.class)) {
//getMethod(),第一个参数为方法名，后边参数是方法中参数的类型，方法中有几个参数就写几个类型
Method method = eClas.getMethod(columnSetMethod, int.class);
//invoke()方法第一个参数是执行方法的对象，第二个是执行方法时的实参
method.invoke(eObj,rs.getInt(i));
}
//字段为字符串类型的
else if (clazz.isAssignableFrom(String.class)) {
Method method = eClas.getMethod(columnSetMethod,String.class);
method.invoke(eObj,rs.getString(i));
}
//字段为double类型
else if (clazz.isAssignableFrom(double.class)) {
Method method = eClas.getMethod(columnSetMethod,double.class);
method.invoke(eObj,rs.getDouble(i));
} //字段为float类型
else if (clazz.isAssignableFrom(float.class)) {
Method method = eClas.getMethod(columnSetMethod,float.class);
method.invoke(eObj,rs.getFloat(i));
}//字段为Integer类型
else if (clazz.isAssignableFrom(Integer.class)) {
Method method = eClas.getMethod(columnSetMethod,Integer.class);
method.invoke(eObj,rs.getInt(i));
}//字段为Float类型
else if (clazz.isAssignableFrom(Float.class)) {
Method method = eClas.getMethod(columnSetMethod,Float.class);
method.invoke(eObj,rs.getFloat(i));
}//字段为double类型
else if (clazz.isAssignableFrom(Double.class)) {
Method method = eClas.getMethod(columnSetMethod,Double.class);
method.invoke(eObj,rs.getDouble(i));
}//字段为Date类型
else if (clazz.isAssignableFrom(Date.class)) {
Method method = eClas.getMethod(columnSetMethod,Date.class);
method.invoke(eObj,rs.getDate(i));
}
}
list.add(eObj);
}
} catch (SQLException e0) {
e0.printStackTrace();
} catch (IllegalAccessException e1) {
e1.printStackTrace();
} catch (InstantiationException e1) {
e1.printStackTrace();
} catch (NoSuchFieldException e1) {
e1.printStackTrace();
} catch (NoSuchMethodException e1) {
e1.printStackTrace();
} catch (InvocationTargetException e1) {
e1.printStackTrace();
}
return list;
}

public static void main(String[] args) {
String sql = "select * from title"; //查询sql
List<Title> list = getObjectBySql(sql,new Title());
for (Title title:list) {
System.out.println(title);
}
}
}
}

Title实体类

/**
* Created by HaoWeiTao on 2017/5/15.
*/
public class Title {
private int id;
private int titleId;
private String titleName;
private double beilv;
private int isEffective;

public Title() {
}

public Title(int id, int titleId, String titleName, double beilv, int isEffective) {
this.id = id;
this.titleId = titleId;
this.titleName = titleName;
this.beilv = beilv;
this.isEffective = isEffective;
}

public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}

public int getTitleId() {
return titleId;
}

public void setTitleId(int titleId) {
this.titleId = titleId;
}

public String getTitleName() {
return titleName;
}

public void setTitleName(String titleName) {
this.titleName = titleName;
}

public double getBeilv() {
return beilv;
}

public void setBeilv(double beilv) {
this.beilv = beilv;
}

public int getIsEffective() {
return isEffective;
}

public void setIsEffective(int isEffective) {
this.isEffective = isEffective;
}

@Override
public String toString() {
return "Title{" +
"id=" + id +
", titleId=" + titleId +
", titleName=" + titleName +
", beilv=" + beilv +
", isEffective=" + isEffective +
'}';
}
}

下面是数据库源数据

`

下面是运行结果

`

《对应jar包有mysql-connect和dbcp》