mysql的java数据库连接错误
我正在尝试使用eclipse在EclipseJuno中进行java数据库连接,但出现以下错误mysql的java数据库连接错误,java,mysql,Java,Mysql,我正在尝试使用eclipse在EclipseJuno中进行java数据库连接,但出现以下错误 java.lang.ClassNotFoundException: com.mysql.jdbc.Driver java.lang.NullPointerException 建议我一些解决方案。。。。。。。。。。 这是我的代码: package example; import java.sql.Connection; import java.sql.DriverManager; import jav
java.lang.ClassNotFoundException: com.mysql.jdbc.Driver
java.lang.NullPointerException
建议我一些解决方案。。。。。。。。。。
这是我的代码:
package example;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
public class Connect {
public static Connection getConnection()
{
String url="jdbc:mysql://localhost:3306/demo";
String drive="com.mysql.jdbc.Driver";
//String databse="demo";
String user="root";
String password="abc";
Connection conn=null;
try
{
Class.forName(drive);
conn=DriverManager.getConnection(url, user, password);
}
catch (Exception e)
{
System.out.println(""+e);
}
return conn;
}
public static void main(String[] args)
{
Connection conn=null;
PreparedStatement pstmt=null;
try
{
conn=getConnection();
conn.setAutoCommit(false);
pstmt=conn.prepareStatement("insert into testlongtele(address,name)values(?,?)");
pstmt.setString(0, "NIRAV");
pstmt.setString(1, "KAMANI");
pstmt.executeUpdate();
pstmt.close();
conn.commit();
conn.close();
}
catch(Exception e)
{
System.out.println(""+e);
}
}
}
从
此错误的可能原因是:
1) 类路径中没有mysql-connector.jar。如前所述,这个jar文件包含“com.mysql.jdbc.Driver”类,它必须存在于类路径中,才能成功连接到mysql数据库。您可以从mysql.com下载mysql-connector.jar
2) mysql-connector.jar位于类路径中,但不知何故,您的类路径被覆盖了。
类路径在Java中很棘手,jar中指定的类路径可能会覆盖类路径变量。请参阅Java中类路径的工作原理,以详细了解此问题
3) mysql-connector.jar位于类路径中,但当前用户没有读取权限。
这个问题经常发生在Unix或Linux操作系统中,该系统具有基于用户、组和所有者级别的复杂文件和目录权限。只需获得正确的权限,然后再次运行您的程序。您可以添加:
class.forName(driver).newInstance();
导入java.sql.Connection;
导入java.sql.DriverManager;
导入java.sql.SQLException;
导入com.mindtree.kalinga.exception.ConnectionfailedException;
公共类JdbcConnection{
私有静态JdbcConnection JdbcConnection;
专用静态连接;
私有JdbcConnection(){
}
公共静态JdbcConnection getInstance(){
if(jdbcConnection==null)
jdbcConnection=新的jdbcConnection();
返回jdbc连接;
}
public static void createConnection()引发ConnectionfailedException{
试一试{
dbConnection=DriverManager.getConnection(“jdbc:mysql://localhost:3306/mindtree“、”根“、”Welcome123”);
}捕获(SQLE异常){
抛出新的ConnectionfailedException(“创建到数据库的连接时出错”,e);
}
System.out.println(“与数据库的连接已建立!”);
}
公共静态连接getConnection(){
返回数据库连接;
}
public static void closeConnection()引发ConnectionfailedException{
试一试{
dbConnection.close();
}捕获(SQLE异常){
抛出新的ConnectionfailedException(“连接未正确关闭”,e);
}
}
}
--------------------------------------
主要
--------------------------------------
包com.mindtree.kalinga.controller;
导入java.util.ArrayList;
导入java.util.List;
导入java.util.Scanner;
导入com.mindtree.kalinga.entity.mindtree;
导入com.mindtree.kalinga.exception.ConnectionfailedException;
导入com.mindtree.kalinga.service.Mindtreeservice;
导入com.mindtree.kalinga.serviceimp.Mindtreeserviceimp;
导入com.mindtree.kalinga.utility.jdbc连接;
公共阶级思维模式{
静态扫描仪输入=新扫描仪(系统输入);
静态Mindtreeservice ms=新的Mindtreeserviceimp();
公共静态void main(字符串[]args){
试一试{
JdbcConnection.createConnection();
}捕捉(连接失败异常e){
System.out.println(“无法连接到数据库!正在终止应用程序!”);
e、 printStackTrace();
}
MindtreeMain mm=新的MindtreeMain();
int i=1;
而(i==1){
System.out.println(“1.输入详细信息\n”+“2.获取详细信息\n”+“3.退出”);
int key=in.nextInt();
开关(钥匙){
案例1:
Mindtree m=mm.createminds();
打破
案例2:
List ml=new ArrayList();
毫米显示(毫升);
打破
案例3:
i=0;
打破
违约:
打破
}
}
}
私有Mindtree createminds(){
//TODO自动生成的方法存根
System.out.println(“输入思想id”);
int id=in.nextInt();
in.nextLine();
System.out.println(“输入思想的名称”);
字符串名称=in.nextLine();
System.out.println(“心灵的地址”);
字符串地址=in.nextLine();
Mindtree m=新Mindtree(id、名称、地址);
返回m;
}
专用空白显示(列表){
为(心智树i:心智){
System.out.println(i.getMid());
System.out.println(i.getName());
System.out.println(i.getAddress());
}
}
}
-------------------------------------------------
服务
-------------------------------------------------
导入java.util.List;
导入com.mindtree.kalinga.entity.mindtree;
公共接口Mindtreeservice{
公共空间插入心智(Mindtree m);
公共列表getAllminds();
}
---------------------------------------------
serviceimp
---------------------------------------------
包com.mindtree.kalinga.serviceimp;
导入java.util.List;
导入com.mindtree.kalinga.dao.Mindtreedao;
导入com.mindtree.kalinga.daoimp.Mindtreedaoimp;
导入com.mindtree.kalinga.entity.mindtree;
导入com.mindtree.kalinga.service.Mindtreeservice;
公共类Mindtreeserviceimp实现Mindtreeservice{
Mindtreedao md=新的Mindtreedaoimp();
@凌驾
公共空间插件(Mindtree m){
//TODO自动生成的方法存根
医学博士insertMindToDb(m);
}
@凌驾
公共列表getAllminds(){
//TODO自动生成的方法存根
返回md.getAllMindFromDb();
}
}
--------------------------------------------
刀
--------------------------------------------
导入java.util.List;
导入com.mindtree.kalinga.entity.mindtree;
公共接口Mindtreedao{
公共空间插入mindtodb(mindtreem);
公共列表getAllMindFromDb();
}
-------------------------------------------
达欧姆
-------------------------------------------
包com.mindtree.kalinga.d
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import com.mindtree.kalinga.exception.ConnectionfailedException;
public class JdbcConnection {
private static JdbcConnection jdbcConnection;
private static Connection dbConnection;
private JdbcConnection() {
}
public static JdbcConnection getInstance() {
if (jdbcConnection == null)
jdbcConnection = new JdbcConnection();
return jdbcConnection;
}
public static void createConnection() throws ConnectionfailedException {
try {
dbConnection = DriverManager.getConnection("jdbc:mysql://localhost:3306/mindtree", "root", "Welcome123");
} catch (SQLException e) {
throw new ConnectionfailedException("Error creating the connection to database", e);
}
System.out.println("Connection to db Established!");
}
public static Connection getConnection() {
return dbConnection;
}
public static void closeConnection() throws ConnectionfailedException {
try {
dbConnection.close();
} catch (SQLException e) {
throw new ConnectionfailedException("connection not closed properly", e);
}
}
}
--------------------------------------
Main
--------------------------------------
package com.mindtree.kalinga.controller;
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
import com.mindtree.kalinga.entity.Mindtree;
import com.mindtree.kalinga.exception.ConnectionfailedException;
import com.mindtree.kalinga.service.Mindtreeservice;
import com.mindtree.kalinga.serviceimp.Mindtreeserviceimp;
import com.mindtree.kalinga.utility.JdbcConnection;
public class MindtreeMain {
static Scanner in = new Scanner(System.in);
static Mindtreeservice ms = new Mindtreeserviceimp();
public static void main(String[] args) {
try {
JdbcConnection.createConnection();
} catch (ConnectionfailedException e) {
System.out.println("Not able to connect to database! Terminating application!");
e.printStackTrace();
}
MindtreeMain mm = new MindtreeMain();
int i = 1;
while (i == 1) {
System.out.println("1. to enter the detail\n" + "2. fetch the detail\n" + "3. to exit");
int key = in.nextInt();
switch (key) {
case 1:
Mindtree m = mm.createminds();
break;
case 2:
List<Mindtree> ml = new ArrayList<>();
mm.display(ml);
break;
case 3:
i = 0;
break;
default:
break;
}
}
}
private Mindtree createminds() {
// TODO Auto-generated method stub
System.out.println("enter the id of mind");
int id = in.nextInt();
in.nextLine();
System.out.println("enter the name of mind");
String name = in.nextLine();
System.out.println("ente the address of minds");
String address = in.nextLine();
Mindtree m = new Mindtree(id, name, address);
return m;
}
private void display(List<Mindtree> mind) {
for (Mindtree i : mind) {
System.out.println(i.getMid());
System.out.println(i.getName());
System.out.println(i.getAddress());
}
}
}
-------------------------------------------------
service
-------------------------------------------------
import java.util.List;
import com.mindtree.kalinga.entity.Mindtree;
public interface Mindtreeservice {
public void insertmind(Mindtree m);
public List<Mindtree> getAllminds();
}
---------------------------------------------
serviceimp
---------------------------------------------
package com.mindtree.kalinga.serviceimp;
import java.util.List;
import com.mindtree.kalinga.dao.Mindtreedao;
import com.mindtree.kalinga.daoimp.Mindtreedaoimp;
import com.mindtree.kalinga.entity.Mindtree;
import com.mindtree.kalinga.service.Mindtreeservice;
public class Mindtreeserviceimp implements Mindtreeservice {
Mindtreedao md = new Mindtreedaoimp();
@Override
public void insertmind(Mindtree m) {
// TODO Auto-generated method stub
md.insertMindToDb(m);
}
@Override
public List<Mindtree> getAllminds() {
// TODO Auto-generated method stub
return md.getAllMindFromDb();
}
}
--------------------------------------------
dao
--------------------------------------------
import java.util.List;
import com.mindtree.kalinga.entity.Mindtree;
public interface Mindtreedao {
public void insertMindToDb(Mindtree m);
public List<Mindtree> getAllMindFromDb();
}
-------------------------------------------
daoimp
-------------------------------------------
package com.mindtree.kalinga.daoimp;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;
import com.mindtree.kalinga.dao.Mindtreedao;
import com.mindtree.kalinga.entity.Mindtree;
import com.mindtree.kalinga.utility.JdbcConnection;
import com.mysql.jdbc.Statement;
public class Mindtreedaoimp implements Mindtreedao {
@Override
public void insertMindToDb(Mindtree m) {
Connection con = JdbcConnection.getConnection();
String query = "insert into mindtree values(?,?,?);";
PreparedStatement ps = null;
try {
ps = con.prepareStatement(query);
ps.setInt(1, m.getMid());
ps.setString(2, m.getName());
ps.setString(3, m.getAddress());
} catch (SQLException e) {
// TODO Auto-generated catch block
System.out.println(e.getMessage());
}
}
@Override
public List<Mindtree> getAllMindFromDb() {
// TODO Auto-generated method stub
List<Mindtree> mtl = new ArrayList<Mindtree>();
Connection con = JdbcConnection.getConnection();
String query = "select * from mindtree;";
Statement st = null;
ResultSet rs = null;
try {
st = (Statement) con.createStatement();
rs = st.executeQuery(query);
while (rs.next()) {
Mindtree m = new Mindtree(rs.getInt(1), rs.getString(2), rs.getString(3));
mtl.add(m);
}
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return mtl;
}
}
-----------------------------------------------
exception
package com.mindtree.kalinga.exception;
public class ConnectionfailedException extends Exception {
public ConnectionfailedException() {
super();
// TODO Auto-generated constructor stub
}
public ConnectionfailedException(String arg0, Throwable arg1, boolean arg2, boolean arg3) {
super(arg0, arg1, arg2, arg3);
// TODO Auto-generated constructor stub
}
public ConnectionfailedException(String arg0, Throwable arg1) {
super(arg0, arg1);
// TODO Auto-generated constructor stub
}
public ConnectionfailedException(String arg0) {
super(arg0);
// TODO Auto-generated constructor stub
}
public ConnectionfailedException(Throwable arg0) {
super(arg0);
// TODO Auto-generated constructor stub
}
}
-----------------------------
entity
-----------------------------
package com.mindtree.kalinga.entity;
public class Mindtree {
int Mid;
String name;
String address;
public Mindtree(int mid, String name, String address)
{
Mid = mid;
this.name = name;
this.address = address;
}
public int getMid() {
return Mid;
}
public void setMid(int mid) {
Mid = mid;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getAddress() {
return address;
}
public void setAddress(String address) {
this.address = address;
}
}