Class.forName（“ com.mysql.jdbc.Driver”）。newInstance（）

Question

我在Netbeans
7.2上遇到此错误，它说ClassNotFoundexception和InstantationException。我真的在这个问题上陷入困境。请帮助我。

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();
    }

Answer 1

那么这个简单的方法呢？

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

我也想知道为什么您要用这种方式连接数据库？最好让服务器对其进行管理。

首先context.xml像这样配置（如果您使用的是tomcat）：

<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中的该资源获取连接，如下所示：

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，不要忘记在<CATALINA_BASE>/lib文件夹中编写MySQL JDBC驱动程序jar 文件。