我有以下代码,我正在尝试创建与数据库的连接。 当我运行命令时,我收到错误“无法找到或加载主类onjava ”: java -cp。 ONJava的
我能够运行 javac -classpath“C:\ CATALINA_HOME \ lib *”onjava.java 命令 我的.class和.java文件都在同一目录WEB-INF \ classes \ com \ onjava
onjava.java
package com.onjava;
import java.sql.*;
import javax.naming.InitialContext;
import javax.naming.NamingException;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.sql.*;
import javax.naming.Context;
public class onjava extends HttpServlet {
private DataSource datasource;
public void init(ServletConfig config) throws ServletException {
try {
// Look up the JNDI data source only once at init time
Context envCtx = (Context) new InitialContext().lookup("java:comp/env");
datasource = (DataSource) ((InitialContext) envCtx).lookup("jdbc/testdb");
}
catch (NamingException e) {
e.printStackTrace();
}
}
private Connection getConnection() throws SQLException {
return datasource.getConnection();
}
public void doGet (HttpServletRequest req, HttpServletResponse res) throws ServletException {
Connection connection=null;
try {
connection = getConnection();
//..<do JDBC work>..
if (connection != null) {
String message = "You are connected!";
System.out.println(message);
} else {
System.out.println("Failed to make connection!");
}
}
catch (SQLException sqlException) {
sqlException.printStackTrace();
}
finally {
if (connection != null)
try {connection.close();} catch (SQLException e) {}
}
}
}
修改
我更改了代码并添加了公共类。但是当我运行它时我遇到了同样的错误!
package src;
import java.sql.DriverManager;
import java.sql.Connection;
import java.sql.SQLException;
import java.sql.Statement;
import java.sql.Wrapper;
import java.util.Hashtable;
import java.util.Properties;
import java.io.*;
import javax.activation.DataSource;
import javax.naming.Context;
import javax.naming.InitialContext;
import javax.naming.NamingException;
import oracle.jdbc.pool.OracleDataSource;
public class onjava {
public static void main(String[] argv) throws SQLException, NamingException {
Properties prop = new Properties();
System.setProperty(Context.INITIAL_CONTEXT_FACTORY,"org.apache.naming.java.javaURLContextFactory");
Context initialContext = new InitialContext(prop);
if ( initialContext == null){
System.out.print("JNDI problem. Cannot get InitialContext.");
} else {System.out.print("NO JNDI problemb ");}
// Get DataSource
Context envContext = (Context)initialContext.lookup("java:/comp/env");
DataSource ds = (DataSource)envContext.lookup("jdbc/testdb");
System.out.println("\n -------- Oracle JDBC Connection Testing ------");
try {
Connection jdbcConnection = ((Statement) ds).getConnection();
OracleDataSource ods = ((Wrapper) ds).unwrap(OracleDataSource.class);
jdbcConnection.close();
} catch (SQLException e) {
System.out.println("Connection Failed! Check output console");
e.printStackTrace();
return;
}
String message = "You are connected!";
System.out.println(message);
}
}
答案 0 :(得分:1)
当像这样运行java时,您需要显式声明主类。您的命令应该看起来更像java -cp . com.onjava.onjava
。但是,我也没有看到这个类中的主要方法。您需要指向main方法(即签名public static void main()
)。
顺便说一下,给你的类名称以大写字母(Onjava)开头是合适的惯例。
答案 1 :(得分:0)
好的,从你告诉我的内容来看,你需要在你的项目中附上一个主类。这意味着返回编译器并创建main方法。要添加代码,您需要在主类中执行类似的操作,我将调用onjavaMain
:
public class onjavaMain{
//Main method is this
public static void main(String[] args)
{
//create variable of your onjava class
onjava onJavaConnectToDatabase = new onjava();
onJavaConnectToDatabase.doGet(argument1,argument2);
}
}
现在这不是完整的答案,但是这将让您了解在命令行中运行项目需要执行的操作。