反射的应用，jdbc封装
实现在Java中查询数据库并保存在Java中
1.创建Dept类（要查找的类）
package cn.ljs;
public class Dept {
private int deptno;
private String dname;
private String loc;
public int getDeptno() {
return deptno;
}
public void setDeptno(int deptno) {
this.deptno = deptno;
}
public String getDname() {
return dname;
}
public void setDname(String dname) {
this.dname = dname;
}
public String getLoc() {
return loc;
}
public void setLoc(String loc) {
this.loc = loc;
}
public Dept() {
super();
}
public Dept(int deptno, String dname, String loc) {
super();
this.deptno = deptno;
this.dname = dname;
this.loc = loc;
}
@Override
public String toString() {
return "Dept [deptno=" + deptno + ", dname=" + dname + ", loc=" + loc
+ "]";
}
}
2.自定义的工具类
package cn.ljs.utill;
import java.io.IOException;
import java.io.InputStream;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.Properties;
public class Jdbcutill {
private static String drive = "";
private static String url = "";
private static String user = "";
private static String password = "";
static {
try {
// 以流的形式获取db.properties
InputStream in = Thread.currentThread().getContextClassLoader().getResourceAsStream("db.properties");
// 创建Properties 类，通过load流读取到该对象中
Properties prop = new Properties();
prop.load(in);
drive = prop.getProperty("drive");
url = prop.getProperty("url");
user = prop.getProperty("user");
password = prop.getProperty("password");
System.out.println(drive);
System.out.println(url);
System.out.println(user);
System.out.println(password);
// 1.加载数据库驱动类
Class.forName(drive);
} catch (ClassNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
System.out.println("配置文件失败");
}
}
public static Connection getConnection() {
Connection connection = null;
try {
connection = DriverManager.getConnection(url, user, password);
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return connection;
}
public static void close(Connection conn, PreparedStatement ps, ResultSet rs) {
if (conn != null) {
try {
conn.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 (rs != null) {
try {
rs.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}
3.配置文件
# do not write space drive=oracle.jdbc.driver.OracleDriver url=jdbc:oracle:thin:@127.0.0.1:1521:orcl user=SCOTT password=tiger
4实现在Java中查询数据库并保存在Java中
package cn.ljs; import java.lang.reflect.Field; 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 cn.ljs.utill.Jdbcutill; public class TestUser { public static void main(String[] args) throws Exception { TestUser testUser = new TestUser(); List list = testUser.rowToBean("select * from dept", Dept.class); for (int i = 0; i < list.size(); i++) { Dept dept = (Dept)list.get(i); System.out.println(dept); } } public List rowToBean(String sql,Class cls) throws Exception{ List list = new ArrayList<>(); //调用自定义的方法，加载数据库，创建数据库的连接对象 Connection conn = Jdbcutill.getConnection(); //创建预编译对象，结果集对象 PreparedStatement ps= null; ResultSet rs = null; ps = conn.prepareStatement(sql); rs = ps.executeQuery(); // 每一个rs对象都对应一个ResultSetMetaData对象 ResultSetMetaData metaData = rs.getMetaData(); // 获取查询的列数 int count = metaData.getColumnCount(); //遍历 while(rs.next()){ Object object = cls.newInstance(); for (int i = 0; i < count; i++) { //获取第几列的名字 String fieldName = metaData.getColumnName(i+1).toLowerCase(); //通过类名获取类中的属性的描述 Field field = cls.getDeclaredField(fieldName); //通过类名，拼接的方法名，属性描述的类型获取set方法 Method method = cls.getDeclaredMethod(getSetMethodName(fieldName),field.getType()); //通过结果集获取数据库中的属性值 Object objval = rs.getObject(fieldName); //执行setfangfa(需要类的对象名，数据库的属性值) if (objval != null) { if (objval instanceof Number) { if (field.getType().getName().equals("int") || field.getType().getName().equals("java.lang.Integer")) { method.invoke(object, rs.getInt(fieldName)); } else if (field.getType().getName().equals("long") || field.getType().getName().equals("java.lang.Long")) { method.invoke(object, rs.getLong(fieldName)); } else if (field.getType().getName().equals("double") || field.getType().getName().equals("java.lang.Double")) { method.invoke(object, rs.getDouble(fieldName)); } else if (field.getType().getName().equals("short") || field.getType().getName().equals("java.lang.Short")) { method.invoke(object, rs.getShort(fieldName)); } else if (field.getType().getName().equals("byte") || field.getType().getName().equals("java.lang.Byte")) { method.invoke(object, rs.getByte(fieldName)); } else if (field.getType().getName().equals("float") || field.getType().getName().equals("java.lang.Float")) { method.invoke(object, rs.getFloat(fieldName)); } } else { method.invoke(object, objval); } } //关闭资源 } list.add(object); } Jdbcutill.close(conn, ps, rs); return list; } //拼接set方法名 public String getSetMethodName(String fieldName){ return "set" + fieldName.substring(0,1).toUpperCase() + fieldName.substring(1); } }
