带有MS SQL Server 2008的Java Eclipse
[英]Java Eclipse with MS SQL server 2008
问题描述
I started learning c# with the use of MS SQL server 2008, I'm just wondering if I could implement the 3 layered in jsp? 
我从使用MS SQL Server 2008开始学习c＃，我只是想知道是否可以在jsp中实现3层？
I will have my Data access layer where my connections and methods like (add,delete,view,update) and so on with the Business logic and for the UI. 我将拥有我的数据访问层，在这里我的连接和方法（如（添加，删除，查看，更新）等）以及业务逻辑和UI。
I tried to do it but it can't display the output. 我尝试这样做，但是无法显示输出。 I tried a simple one of adding then viewing the added ones. 我尝试了一种简单的添加方法，然后查看添加的内容。 (No business logic yet) （尚无业务逻辑）
Here is my code: 这是我的代码：
public class DAL { DAL公共类{
public static String driver = "com.microsoft.sqlserver.jdbc.SQLServerDriver";
static String connectionURL = "jdbc:sqlserver://localhost; database = Sample; Integratedsecurity = true";
public void addProduct(String productName){
try {
Class.forName(driver);
Connection con = DriverManager.getConnection(connectionURL);
String sql = "Insert into Products values (?)";
PreparedStatement pst = con.prepareStatement(sql);
pst.setString(1, productName);
pst.closeOnCompletion();
pst.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (ClassNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
public ResultSet viewProduct(){
ResultSet rs = null;
try {
Class.forName(driver);
Connection con = DriverManager.getConnection(connectionURL);
String sql = "Select * from Products";
PreparedStatement pst = con.prepareStatement(sql);
rs = pst.executeQuery();
while(rs.next()){
rs.getInt(2);
}
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (ClassNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return rs;
}
Here is my page where it add the products from the user (i just cut the other parts of html) 这是我在其中添加用户产品的页面（我只是剪切了html的其他部分）
<%!
DAL d = new DAL();
%>
<body>
<%
String productName = request.getParameter("productName") != null ?
request.getParameter("productName") : "No product has been delivered";
d.addProduct(productName);
%>
<h1> Product: <%= d.viewProduct() %> </h1>
</body>
The errors says java.lang.ClassNotFoundException: com.microsoft.sqlserver.jdbc.SQLServerDriver but I have in my classPath the library and I tried not to have a 3 tier just for testing purposes but yet it still not working. 错误显示java.lang.ClassNotFoundException: com.microsoft.sqlserver.jdbc.SQLServerDriver但是我在classPath中拥有该库，并且我尝试不具有仅用于测试目的的3层，但仍然无法正常工作。 The return is Null and classnotfoundexception. 返回值为Null和classnotfoundexception。 Any kind of help would be appreciated. 任何帮助将不胜感激。
2 个解决方案
解决方案1
0 已采纳 2015-04-08 14:26:29
Multiple issues in your code: 您的代码中存在多个问题：
The
addProduct()call is missing anpst.executeUpdate()method on the statement.addProduct()调用在该语句上缺少pst.executeUpdate()方法。 So, the insert will never be run.因此，插入将永远不会运行。 The
viewProduct()call is not closing the obtainedResultSet, this results in dangling resources in the JDBC driver and possibly even on the SQL-server.viewProduct()调用没有关闭获得的ResultSet，这导致JDBC驱动程序中甚至是SQL服务器上的资源悬空。You can manage all calls using one connection, no need to open a new one every run.
您可以使用一个连接管理所有呼叫，而无需每次运行都打开一个新的连接。 Besides that, you are not closing the connections after use. 除此之外，使用后您不会关闭连接。 You should use the new Java syntax for try-with-resources or add a finally block: 您应该将新的Java语法用于try-with-resources或添加一个finally块： try ( Statement st = connection.prepareStatement(sql); ) { // use the statement here ... st.executeUpdate(); } catch(Exception e) { } // st will be closed here Statement st = null; try { st = connection.prepareStatement(sql); } catch(Exception e) { } finally { try { if( st != null ) st.close(); } catch (Exception ex) { throw new RuntimeException("cannot close statement", ex); } }
The general approach is very hackish. 通用的方法非常骇人听闻。 If this is to be a JSP based application, you should consider a connection pool instead of handling the connections on a per call basis. 如果这是基于JSP的应用程序，则应考虑使用连接池，而不是基于每个调用来处理连接。 The connection pool is configured as a Datasource in your web.xml and needs to be configured according to the container you are using (Tomcat, Jetty, ...). 连接池在web.xml中配置为数据源，需要根据您使用的容器（Tomcat，Jetty等）进行配置。
If you are using a container datasource, you will draw the connection from the datasource, not from the JDBC driver directly. 如果使用的是容器数据源，则将从数据源绘制连接，而不是直接从JDBC驱动程序绘制连接。 Otherwise, you should consider a connection pool inside your application, that provides a ready-made connection to you on request. 否则，您应该考虑应用程序内部的连接池，该连接池可应要求为您提供现成的连接。
Having said this: 话虽如此：
Where do you place the jar file for the SQL driver? 您将SQL驱动程序的jar文件放在哪里？ The way you call it, it should be in the WEB-INF/lib folder of your web application. 调用方式应位于Web应用程序的WEB-INF/lib文件夹中。
解决方案2
0 2015-04-08 14:37:19
First thing to make sure is that the sqlserver library is correctly set in the build path. 首先要确保的是在构建路径中正确设置了sqlserver库。 To access/update/delete entries from your database, try the following: 要访问/更新/删除数据库中的条目，请尝试以下操作：
Connection conn = null;
Statement stmt = null;
try {
// Register JDBC driver
Class.forName("com.microsoft.sqlserver.jdbc.SQLServerDriver");
conn = DriverManager.getConnection(DB_URL, USER, PASSWORD);
stmt = conn.createStatement();
String sql = "Enter your update query";
stmt.executeUpdate(sql);
// Extract all the records to see the updated records
sql = "Enter your select query";
ResultSet rs = stmt.executeQuery(sql);
while (rs.next()) {
// Retrieve data by column name in your database
String username = rs.getString("enter relevant column name from database");
int logintries = rs.getInt("enter relevant column name from database");
// Display values to console
System.out.print("Username : " + username);
System.out.print(", Login Tries : " + logintries);
}
rs.close();
} catch (SQLException se) {
se.printStackTrace();
} catch (Exception e) {
e.printStackTrace();
}
If the ms sqlserver library is set correctly, this should work for you too. 如果ms sqlserver库设置正确，这也应该为您工作。 Hope it helps... 希望能帮助到你...
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