我一直在尝试使用 Velocity 创建一个 HTML 页面，该页面显示存储在名为 users 的 SQL 表中的名称。当我运行程序时，它会打印以下堆栈跟踪:
java.sql.SQLException
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1055)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:956)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:926)
at com.mysql.jdbc.ResultSetImpl.checkRowPos(ResultSetImpl.java:815)
at com.mysql.jdbc.ResultSetImpl.getStringInternal(ResultSetImpl.java:5528)
at com.mysql.jdbc.ResultSetImpl.getString(ResultSetImpl.java:5448)
at com.mysql.jdbc.ResultSetImpl.getString(ResultSetImpl.java:5488)
at com.sarvika.velocity.HelloWorld.CfNMHTMLParser.main(CfNMHTMLParser.java:41)
我确信我确实导入了所有必需的库和 MySQL 连接驱动程序。我正在使用 mysql-connector-java-5.1.6 来达到目的。我的代码是:
package com.sarvika.velocity.dbtovelocity;
import java.io.*;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import org.apache.velocity.*;
import org.apache.velocity.app.VelocityEngine;
public class CfNMHTMLParser {
private final static String URL = "jdbc:mysql://localhost/coffeenet";
private final static String USER = "root";
private final static String PASS = "root";
private static final String BOOL_EXC = "exception";
private static final String EXC = "exc";
private static final String USER_LIST = "usersArray";
public static void main (String [] args)
throws IOException {
VelocityEngine engine = new VelocityEngine();
Template template = engine.getTemplate("HTMLTemplate.vm");
VelocityContext context = new VelocityContext();
CfNMHTMLParser parser = new CfNMHTMLParser();
String [] data = null ;
try {
Connection conn = DriverManager.getConnection(URL, USER, PASS);
Statement stmt = conn.createStatement();
String query = "SELECT count(*) FROM users ;";
ResultSet rs = stmt.executeQuery(query);
int count = Integer.parseInt(rs.getString("count(*)"));
data = new String[count];
query = "SELECT AuthID FROM users ;";
rs = stmt.executeQuery(query);
for (int i = 0 ; i < count ; i++) {
rs.next();
data[i] = rs.getString("AuthID");
}
// data = new String [] {
// "developers",
// "developers",
// "developers",
// "developers"
// };
} catch (SQLException ex) {
ex.printStackTrace();
context.put(BOOL_EXC, true);
context.put(EXC, ex.getMessage());
}
context.put(USER_LIST, data);
StringWriter templateData = new StringWriter();
template.merge(context, templateData);
File htmlFile = new File("page.html");
FileWriter fileWriter = new FileWriter(htmlFile);
BufferedWriter writer = new BufferedWriter(fileWriter);
writer.write(templateData.toString());
writer.close();
}
}
文件 HTMLTemplate.vm
#macro( makeUserTable $userListObjArray )
#foreach( $user in $userListObjArray )
<font size="7" color="ffccaa">
$user
</font>
<BR>
#end
#end
<html>
<title>CoffeeNet Messenger Users</title>
#if ($exception == true)
<font size="48">Exception : $exc </font>
#else
#makeUserTable( $usersArray )
#end
</html>
请告诉我哪里出错了......
最佳答案
错误出现在这行 rs.getString("count(*)") 中，因此您可以更改这两行:
String query = "SELECT count(*) FROM users ;";
...
int count = Integer.parseInt(rs.getString("count(*)"));
分别在:
String query = "SELECT count(*) as tot FROM users ;";
...
int count = Integer.parseInt(rs.getString("tot"));
对于 Velocity，我认为你必须初始化，这样你就可以添加这一行:
VelocityEngine engine = new VelocityEngine();
engine.init(); // line to add
Template template = engine.getTemplate("HTMLTemplate.vm");
关于java - MySQL 数据库连接速度无法正常工作，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/27577773/