JDBC之利用反射技术将查询结果封装为对象

1、User.java中的代码

package cn.itcast.jdbc.domain;

import java.util.Date;

/**
 * 用户对象
 */
public class User {
private int id;
private String name;
private Date birthday;
private float money;

public User() {
}

public User(String name) {
this.name = name;
}

public User(float money) {
this.money = money;
}

public void showName() {
System.out.println(this.name);
}

public int getId() {
return id;
}

public void setId(Integer id) {
this.id = id;
}

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public Date getBirthday() {
return birthday;
}

public void setBirthday(java.sql.Date birthday) {
this.birthday = birthday;
}

public float getMoney() {
return money;
}

public void setMoney(Float money) {
this.money = money;
}

}

2、测试类ORMTest.java中的代码

package cn.itcast.jdbc;

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;

import org.junit.Test;

import cn.itcast.jdbc.domain.User;

/**
 * 利用Java反射技术将查询结果封装为对象
 */
public class ORMTest {

/**
 * 测试封装单个对象
 * @throws InstantiationException
 * @throws IllegalAccessException
 * @throws NoSuchMethodException
 * @throws SecurityException
 * @throws IllegalArgumentException
 * @throws InvocationTargetException
 * @throws SQLException
 */
@Test
public void testGetObject() throws 
InstantiationException, IllegalAccessException, 
NoSuchMethodException, SecurityException, 
IllegalArgumentException, InvocationTargetException, 
SQLException {
User user = (User) getObject(
"select id as Id, name as Name, birthday as Birthday, "
+ "money as Money  from user where id=1",
User.class);
System.out.println(user);
}

/**
 * 测试将对象封装进List集合中
 * @throws InstantiationException
 * @throws IllegalAccessException
 * @throws IllegalArgumentException
 * @throws InvocationTargetException
 * @throws SQLException
 */
@Test
public void testGetObjects() throws 
InstantiationException, IllegalAccessException, 
IllegalArgumentException, InvocationTargetException, 
SQLException {
List<Object> list = getObjects("select id as Id, name as Name, birthday as Birthday, "
+ "money as Money  from user where id=1",
User.class);
System.out.println(list.size());
}


/**
 * 测试封装多个对象
 * @param sql
 * @param clazz
 * @return
 * @throws SQLException
 * @throws InstantiationException
 * @throws IllegalAccessException
 * @throws IllegalArgumentException
 * @throws InvocationTargetException
 */
static List<Object> getObjects(String sql, @SuppressWarnings("rawtypes") Class clazz) 
throws SQLException, InstantiationException, 
IllegalAccessException, IllegalArgumentException, 
InvocationTargetException {

Connection conn = null;
PreparedStatement ps = null;
ResultSet rs = null;

try {
conn = JdbcUtils.getConnection();
ps = conn.prepareStatement(sql);
rs = ps.executeQuery();
String[] colNames = getColNames(rs);

List<Object> objects = new ArrayList<Object>();
//获取所有的公共方法
Method[] ms = clazz.getMethods();
while(rs.next()) {
//创建一个新对象
Object object = clazz.newInstance();
for(int i = 0; i < colNames.length; i ++) {
String colName = colNames[i];
//获取set方法的方法名
String methodName = "set" + colName;
for(Method m : ms) {
if(methodName.equals(m.getName())) {
m.invoke(object, rs.getObject(colName));
break;
}
}
objects.add(object);
}
}
return objects;
} finally {
JdbcUtils.free(rs, ps, conn);
}
}

/**
 * 根据结果集获取查询结果的别名
 * @param rs
 * @return
 * @throws SQLException
 */
private static String[] getColNames(ResultSet rs) throws SQLException {
ResultSetMetaData rsmd = rs.getMetaData();
//获取查询的列数
int count = rsmd.getColumnCount();
String[] colNames = new String[count];
for(int i = 1; i <= count; i ++) {
//获取查询类的别名
colNames[i - 1] = rsmd.getColumnLabel(i);
}
return colNames;
}

/**
 * 封装单个对象
 * @param sql
 * @param clazz
 * @return
 * @throws SQLException
 * @throws InstantiationException
 * @throws IllegalAccessException
 * @throws NoSuchMethodException
 * @throws SecurityException
 * @throws IllegalArgumentException
 * @throws InvocationTargetException
 */
static Object getObject(String sql, @SuppressWarnings("rawtypes") Class clazz) 
throws SQLException, InstantiationException, 
IllegalAccessException, NoSuchMethodException, 
SecurityException, IllegalArgumentException, 
InvocationTargetException {
Connection conn = null;
PreparedStatement ps = null;
ResultSet rs = null;

try {
conn = JdbcUtils.getConnection();
ps = conn.prepareStatement(sql);
rs = ps.executeQuery();
String[] colNames = getColNames(rs);

Object object = null;
Method[] ms = clazz.getMethods();
if(rs.next()) {
object = clazz.newInstance();
for(int i = 0; i < colNames.length; i ++) {
String colName = colNames[i];
String methodName = "set" + colName;

//直接根据方法名获取对应的Method对象
/*Object value = rs.getObject(colName);
@SuppressWarnings("unchecked")
Method m = clazz.getMethod(methodName, value.getClass());
if(m != null) {
m.invoke(object, value);
}*/

for(Method md : ms) {
if(methodName.equals(md.getName())) {
md.invoke(object, rs.getObject(colName));
break;
}
}
}
}
return object;
} finally {
JdbcUtils.free(rs, ps, conn);
}
}

}