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);
} }