我有连接到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。看起来我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
我已经直接在 MySQL Workbench 中尝试过这个调用，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”）。这是我到目前为止所拥有的：
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
从我的 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 {
}
}
我的持久性课程：
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;
}
}
持久性.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>