封装一个工具类,用来实现jdbc
package contemplate;
//封装起来的工具类
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;public final class JDBC_utils { private static String url="jdbc:mysql://localhost:3306/test";
private static String user="root";
private static String password="lycy";
public JDBC_utils(){}
static{
try{
Class.forName("com.mysql.jdbc.Driver");
}catch(ClassNotFoundException e){
throw new ExceptionInInitializerError(e);
}
}
public static Connection getConnection() throws SQLException
{
return DriverManager.getConnection(url, user, password);
}
public static void free(ResultSet rs,Statement st,Connection conn)
{
try{
if(rs!=null)
rs.close();
}catch(SQLException e){
e.printStackTrace();
}finally{
try{
if(st!=null)
st.close();
}catch(SQLException e){
e.printStackTrace();
}finally{
if(conn!=null)
try{
conn.close();
}catch(SQLException e){
e.printStackTrace();
}
}
}
}
}
下面是实现代码:
package contemplate;import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.Statement;public class Base { /**
* @param args
* @throws Exception
*/
public static void main(String[] args) throws Exception {
// TODO Auto-generated method stub
template();
}
static void template() throws Exception{
Connection conn=null;
Statement st=null;
ResultSet rs=null;
try{
//建立连接
conn=JDBC_utils.getConnection();
//创建语句
st=conn.createStatement();
//执行语句
rs=st.executeQuery("select *from user");
//处理结果
while (rs.next()){
System.out.println(rs.getObject(1)+ "\t" + rs.getObject(2)
+ "\t" + rs.getObject(3) + "\t" );
}
}finally{
JDBC_utils.free(rs, st, conn);
}
}
}
出现的错误信息是:Exception in thread "main" java.lang.NoClassDefFoundError: Could not initialize class contemplate.JDBC_utils
at contemplate.Base.template(Base.java:37)
at contemplate.Base.main(Base.java:17)求解~各位大神请帮忙~
package contemplate;
//封装起来的工具类
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;public final class JDBC_utils { private static String url="jdbc:mysql://localhost:3306/test";
private static String user="root";
private static String password="lycy";
public JDBC_utils(){}
static{
try{
Class.forName("com.mysql.jdbc.Driver");
}catch(ClassNotFoundException e){
throw new ExceptionInInitializerError(e);
}
}
public static Connection getConnection() throws SQLException
{
return DriverManager.getConnection(url, user, password);
}
public static void free(ResultSet rs,Statement st,Connection conn)
{
try{
if(rs!=null)
rs.close();
}catch(SQLException e){
e.printStackTrace();
}finally{
try{
if(st!=null)
st.close();
}catch(SQLException e){
e.printStackTrace();
}finally{
if(conn!=null)
try{
conn.close();
}catch(SQLException e){
e.printStackTrace();
}
}
}
}
}
下面是实现代码:
package contemplate;import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.Statement;public class Base { /**
* @param args
* @throws Exception
*/
public static void main(String[] args) throws Exception {
// TODO Auto-generated method stub
template();
}
static void template() throws Exception{
Connection conn=null;
Statement st=null;
ResultSet rs=null;
try{
//建立连接
conn=JDBC_utils.getConnection();
//创建语句
st=conn.createStatement();
//执行语句
rs=st.executeQuery("select *from user");
//处理结果
while (rs.next()){
System.out.println(rs.getObject(1)+ "\t" + rs.getObject(2)
+ "\t" + rs.getObject(3) + "\t" );
}
}finally{
JDBC_utils.free(rs, st, conn);
}
}
}
出现的错误信息是:Exception in thread "main" java.lang.NoClassDefFoundError: Could not initialize class contemplate.JDBC_utils
at contemplate.Base.template(Base.java:37)
at contemplate.Base.main(Base.java:17)求解~各位大神请帮忙~
解决方案 »
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