的Class.forName（QUOT; com.mysql.jdbc.Driver&QUOT）的newInstance（）。 [英] Class.forName("com.mysql.jdbc.Driver").newInstance()

问题描述

我在Netbeans 7.2上遇到这个错误，它说ClassNotFoundexception和InstantationException。我真的被这个问题困住了。请帮助我。

I am having this error on Netbeans 7.2, it says that ClassNotFoundexception and InstantationException. I am really stuck on this matter. Kindly help me.

protected void doPost(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    try {
        String driver = "com.mysql.jdbc.Driver";
        con = null;
        String username = "";
        String password = "";

        Class.forName("com.mysql.jdbc.Driver").newInstance();

        con = DriverManager.getConnection("jdbc:mysql://localhost:3306/dbName", "root", "password");
        Statement st = con.createStatement();
        ResultSet mar = st.executeQuery("SELECT * FROM table");


        Gson gson = new GsonBuilder().create();
        response.setContentType("application/json");  
        response.setCharacterEncoding("utf-8"); 

    } catch (SQLException e) {
                String message = e.getMessage();
    }

推荐答案

这个简单的方法怎么样？ ！

What about this simple way?!

java.sql.Driver d=new com.mysql.jdbc.Driver();

我也想知道你为什么用这种方式连接到数据库？！让服务器管理它会更好。

I also wondered why do you connect to database with such this way?! It's better let server manage it.

首先配置 context.xml （如果你使用的是tomcat）就像这样：

First config the context.xml (if you are using tomcat) like this:

<context>
<Resource name="_ds" auth="Container" type="javax.sql.DataSource"
               maxActive="128" maxIdle="32" username="_admin" password="qwerty" driverClassName="com.mysql.jdbc.Driver"
               url="jdbc:mysql://127.0.0.1:3306/dbname"/>
</context>

然后，简单地从servlet / etc中获取此资源的连接，如下所示：

Then, simple get a connection from this resource in servlet/etc, like this:

public void init() {
    try {
        _ds = (DataSource) InitialContext.lookup("java:/comp/env/_ds");
    } catch (Exception ex) {
    }
}

private javax.sql.DataSource _ds;

protected void doPost(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException
{
    try {
        /*String driver = "com.mysql.jdbc.Driver";
        con = null;
        String username = "";
        String password = "";

        Class.forName("com.mysql.jdbc.Driver").newInstance();

        con = DriverManager.getConnection("jdbc:mysql://localhost:3306/dbName", "root", "password");*/
        Connection con=_ds.getConnection();
        Statement st = con.createStatement();
        ResultSet mar = st.executeQuery("SELECT * FROM table");


        Gson gson = new GsonBuilder().create();
        response.setContentType("application/json");  
        response.setCharacterEncoding("utf-8"); 
        con.close();
    } catch (SQLException e) {
        String message = e.getMessage();
    }

顺便说一句，不要忘记编写MySQL JDBC驱动程序jar-文件在< CATALINA_BASE> / lib 文件夹中。

By the way, don't forget to compy the MySQL JDBC driver jar-file in <CATALINA_BASE>/lib folder.

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