【发布时间】：2013-09-19 22:04:53
【问题描述】：
我的数据库正在运行。我可以毫无问题地执行以下操作：
Class.forName("com.mysql.jdbc.Driver");
Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/people", "root", "r00t");
PreparedStatement statement = (PreparedStatement) conn.prepareStatement("select * from users");
ResultSet result = statement.executeQuery();
但是，在设置 JPA 和持久类之后，我总是收到“未选择数据库”错误。我似乎不需要调整我的数据库配置（MySQL 连接到 Glassfish 3.1），否则上面的代码将不起作用。
正在拨打的电话：
SELECT USERNAME, FIRSTNAME, LASTNAME, PASSWORD, PERMISSION FROM users
我已经在 MySQL Workbench 中直接尝试过这个调用，但它不起作用。
这个确实有效：
SELECT USERNAME, FIRSTNAME, LASTNAME, PASSWORD, PERMISSION FROM people.users
我一直在玩，似乎无法在任何地方添加数据库名称（“人”）。 这是我目前所拥有的：
使用 EclipseLink 2.0.x
JPA 实现：禁用库配置
连接：本地 MySQL（我的数据库已成功连接）
架构：人
来自我的 servlet：
package com.lowe.samples;
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import com.mysql.jdbc.PreparedStatement;
@WebServlet("/TestServlet")
public class TestServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
@PersistenceContext
private EntityManager em;
public TestServlet() {
super();
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
PrintWriter out = response.getWriter();
out.println("<h1>DataBase Test:<h1>");
try {
Class.forName("com.mysql.jdbc.Driver");
Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/people", "root", "r00t");
PreparedStatement statement = (PreparedStatement) conn.prepareStatement("select * from users");
ResultSet result = statement.executeQuery();
// prep the table
out.print("<table border=\"5\">");
out.print("<tr>");
out.print("<td>UserName</td>");
out.print("<td>FirstName</td>");
out.print("<td>LastName</td>");
out.print("<td>Password</td>");
out.print("<td>Permission</td>");
out.print("</tr>");
while(result.next()) {
out.print("<tr>");
out.print("<td>" + result.getString(1) + "</td>");
out.print("<td>" + result.getString(2) + "</td>");
out.print("<td>" + result.getString(3) + "</td>");
out.print("<td>" + result.getString(4) + "</td>");
out.print("<td>" + result.getString(5) + "</td>");
out.print("</tr>");
}
out.print("</table>");
User u = (User)this.em.createNamedQuery("User.findAll").getResultList();
out.print("User Name: " + u.getFirstName());
} catch (ClassNotFoundException e) {
out.print("<h4>" + e.getMessage() + "</h4>");
e.printStackTrace();
} catch (SQLException e) {
out.print("<h4>" + e.getMessage() + "</h4>");
e.printStackTrace();
}
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
}
}
我的持久化类：
package com.lowe.samples;
import java.io.Serializable;
import javax.persistence.*;
/**
* The persistent class for the users database table.
*/
@Entity
@Table(name="users")
@NamedQuery(name="User.findAll", query="SELECT u FROM User u")
public class User implements Serializable {
private static final long serialVersionUID = 1L;
@Id
private String userName;
private String firstName;
private String permission;
private String lastName;
private String password;
public User() {
}
public String getUserName() {
return this.userName;
}
public void setUserName(String userName) {
this.userName = userName;
}
public String getFirstName() {
return this.firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public String getPermission() {
return this.permission;
}
public void setPermission(String permission) {
this.permission = permission;
}
public String getLastName() {
return this.lastName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
public String getPassword() {
return this.password;
}
public void setPassword(String password) {
this.password = password;
}
}
persistence.xml
<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.0" xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd">
<persistence-unit name="MyFriends">
<jta-data-source>jdbc/MySQLDataSource</jta-data-source>
<class>com.lowe.samples.User</class>
</persistence-unit>
</persistence>
【问题讨论】：
-
你为什么用jdbc？
-
@nachokk 我不关注。与否？
-
如果您使用的是 jpa，您将把这项工作委托给您正在使用的提供商。在您的情况下，toplink。 jpa or jdbc
-
@nachokk 我使用 JDBC 代码来证明我的数据库连接已启动。当我正确集成 JPA 时，我不打算保留它。
标签： java mysql jpa glassfish-3