在上一章中,我们创建了一个示例RMI应用程序,其中客户端调用显示GUI窗口(JavaFX)的方法.
在本章中,我们将举例说明看看客户端程序如何检索驻留在服务器上的MySQL数据库中表的记录.
假设我们在数据库中有一个名为 student_data 的表详情如下所示.
+----+--------+--------+------------+---------------------+ | ID | NAME | BRANCH | PERCENTAGE | EMAIL | +----+--------+--------+------------+---------------------+ | 1 | Ram | IT | 85 | ram123@gmail.com | | 2 | Rahim | EEE | 95 | rahim123@gmail.com | | 3 | Robert | ECE | 90 | robert123@gmail.com | +----+--------+--------+------------+---------------------+
假设用户名是 myuser ,密码是密码.
使用创建学生课程setter 和 getter 方法如下所示.
public class Student implements java.io.Serializable { private int id, percent; private String name, branch, email; public int getId() { return id; } public String getName() { return name; } public String getBranch() { return branch; } public int getPercent() { return percent; } public String getEmail() { return email; } public void setID(int id) { this.id = id; } public void setName(String name) { this.name = name; } public void setBranch(String branch) { this.branch = branch; } public void setPercent(int percent) { this.percent = percent; } public void setEmail(String email) { this.email = email; } }
定义远程接口.在这里,我们定义了一个名为 Hello 的远程接口,其中包含一个名为 getStudents()的方法.此方法返回一个列表,其中包含类 Student 的对象.
import java.rmi.Remote; import java.rmi.RemoteException; import java.util.*; // Creating Remote interface for our application public interface Hello extends Remote { public List<Student> getStudents() throws Exception; }
创建一个类并实现上面创建的接口.
这里我们正在实现远程接口的 getStudents()方法.当您调用此方法时,它将检索名为 student_data 的表的记录.使用setter方法将这些值设置为Student类,将其添加到列表对象并返回该列表.
import java.sql.*; import java.util.*; // Implementing the remote interface public class ImplExample implements Hello { // Implementing the interface method public List<Student> getStudents() throws Exception { List<Student> list = new ArrayList<Student>(); // JDBC driver name and database URL String JDBC_DRIVER = "com.mysql.jdbc.Driver"; String DB_URL = "jdbc:mysql://localhost:3306/details"; // Database credentials String USER = "myuser"; String PASS = "password"; Connection conn = null; Statement stmt = null; //Register JDBC driver Class.forName("com.mysql.jdbc.Driver"); //Open a connection System.out.println("Connecting to a selected database..."); conn = DriverManager.getConnection(DB_URL, USER, PASS); System.out.println("Connected database successfully..."); //Execute a query System.out.println("Creating statement..."); stmt = conn.createStatement(); String sql = "SELECT * FROM student_data"; ResultSet rs = stmt.executeQuery(sql); //Extract data from result set while(rs.next()) { // Retrieve by column name int id = rs.getInt("id"); String name = rs.getString("name"); String branch = rs.getString("branch"); int percent = rs.getInt("percentage"); String email = rs.getString("email"); // Setting the values Student student = new Student(); student.setID(id); student.setName(name); student.setBranch(branch); student.setPercent(percent); student.setEmail(email); list.add(student); } rs.close(); return list; } }
RMI服务器程序应实现远程接口或者扩展实现类.在这里,我们应该创建一个远程对象并将其绑定到 RMI注册表.
以下是此应用程序的服务器程序.在这里,我们将扩展上面创建的类,创建一个远程对象并使用绑定名称 hello 将其注册到RMI注册表.
import java.rmi.registry.Registry; import java.rmi.registry.LocateRegistry; import java.rmi.RemoteException; import java.rmi.server.UnicastRemoteObject; public class Server extends ImplExample { public Server() {} public static void main(String args[]) { try { // Instantiating the implementation class ImplExample obj = new ImplExample(); // Exporting the object of implementation class ( here we are exporting the remote object to the stub) Hello stub = (Hello) UnicastRemoteObject.exportObject(obj, 0); // Binding the remote object (stub) in the registry Registry registry = LocateRegistry.getRegistry(); registry.bind("Hello", stub); System.err.println("Server ready"); } catch (Exception e) { System.err.println("Server exception: " + e.toString()); e.printStackTrace(); } } }
以下是客户本申请的程序.在这里,我们获取远程对象并调用名为 getStudents()的方法.它从列表对象中检索表的记录并显示它们.
import java.rmi.registry.LocateRegistry; import java.rmi.registry.Registry; import java.util.*; public class Client { private Client() {} public static void main(String[] args)throws Exception { try { // Getting the registry Registry registry = LocateRegistry.getRegistry(null); // Looking up the registry for the remote object Hello stub = (Hello) registry.lookup("Hello"); // Calling the remote method using the obtained object List<Student> list = (List)stub.getStudents(); for (Student s:list)v { // System.out.println("bc "+s.getBranch()); System.out.println("ID: " + s.getId()); System.out.println("name: " + s.getName()); System.out.println("branch: " + s.getBranch()); System.out.println("percent: " + s.getPercent()); System.out.println("email: " + s.getEmail()); } // System.out.println(list); } catch (Exception e) { System.err.println("Client exception: " + e.toString()); e.printStackTrace(); } } }
关注是运行我们的RMI示例的步骤.
步骤1 : 打开存储所有程序的文件夹并编译所有Java文件,如下所示.
Javac * .java
第2步 : 使用以下命令启动 rmi 注册表.
start rmiregistry
这将开始一个单独的窗口上的 rmi 注册表,如下所示.
第3步 : 运行服务器类文件,如下所示.
Java Server
第4步&减号;运行客户端类文件,如下所示.
java Client