Java Mysql 简明教程

Java & MySQL - Navigating a ResultSet

ResultSet 接口中有几种方法涉及移动光标，包括 -

There are several methods in the ResultSet interface that involve moving the cursor, including −

S.N.

Methods & Description

1

*public void beforeFirst() throws SQLException *Moves the cursor just before the first row.

2

*public void afterLast() throws SQLException *Moves the cursor just after the last row.

3

*public boolean first() throws SQLException *Moves the cursor to the first row.

4

*public void last() throws SQLException *Moves the cursor to the last row.

5

*public boolean absolute(int row) throws SQLException*Moves the cursor to the specified row.

6

*public boolean relative(int row) throws SQLException *Moves the cursor the given number of rows forward or backward, from where it is currently pointing.

7

*public boolean previous() throws SQLException *Moves the cursor to the previous row. This method returns false if the previous row is off the result set.

8

*public boolean next() throws SQLException *Moves the cursor to the next row. This method returns false if there are no more rows in the result set.

9

*public int getRow() throws SQLException *Returns the row number that the cursor is pointing to.

10

*public void moveToInsertRow() throws SQLException *Moves the cursor to a special row in the result set that can be used to insert a new row into the database. The current cursor location is remembered.

11

*public void moveToCurrentRow() throws SQLException *Moves the cursor back to the current row if the cursor is currently at the insert row; otherwise, this method does nothing

下面是使用所描述的一些导航方法的示例。

Following is the example which makes use of few navigation methods described.

此示例代码基于先前章节中完成的环境和数据库设置编写。

This sample code has been written based on the environment and database setup done in the previous chapters.

将以下示例复制并粘贴到 TestApplication.java 中，如下进行编译和运行：

Copy and paste the following example in TestApplication.java, compile and run as follows −

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

public class TestApplication {
   static final String DB_URL = "jdbc:mysql://localhost/TUTORIALSPOINT";
   static final String USER = "guest";
   static final String PASS = "guest123";
   static final String QUERY = "SELECT id, first, last, age FROM Employees";

   public static void main(String[] args) {
      // Open a connection
      try(Connection conn = DriverManager.getConnection(DB_URL, USER, PASS);
         Statement stmt = conn.createStatement(
         ResultSet.TYPE_SCROLL_INSENSITIVE,
         ResultSet.CONCUR_READ_ONLY);
         ResultSet rs = stmt.executeQuery(QUERY);
      ) {
         // Move cursor to the last row.
         System.out.println("Moving cursor to the last...");
         rs.last();

         // Extract data from result set
         System.out.println("Displaying record...");
         //Retrieve by column name
         int id  = rs.getInt("id");
         int age = rs.getInt("age");
         String first = rs.getString("first");
         String last = rs.getString("last");

         // Display values
         System.out.print("ID: " + id);
         System.out.print(", Age: " + age);
         System.out.print(", First: " + first);
         System.out.println(", Last: " + last);

         // Move cursor to the first row.
         System.out.println("Moving cursor to the first row...");
         rs.first();

         // Extract data from result set
         System.out.println("Displaying record...");
         // Retrieve by column name
         id  = rs.getInt("id");
         age = rs.getInt("age");
         first = rs.getString("first");
         last = rs.getString("last");

         // Display values
         System.out.print("ID: " + id);
         System.out.print(", Age: " + age);
         System.out.print(", First: " + first);
         System.out.println(", Last: " + last);
         // Move cursor to the first row.

         System.out.println("Moving cursor to the next row...");
         rs.next();

         // Extract data from result set
         System.out.println("Displaying record...");
         id  = rs.getInt("id");
         age = rs.getInt("age");
         first = rs.getString("first");
         last = rs.getString("last");

         // Display values
         System.out.print("ID: " + id);
         System.out.print(", Age: " + age);
         System.out.print(", First: " + first);
         System.out.println(", Last: " + last);

      } catch (SQLException e) {
         e.printStackTrace();
      }
   }
}

现在让我们如下编译上述示例：

Now let us compile the above example as follows −

C:\>javac TestApplication.java
C:\>

运行 TestApplication 时，它会生成以下结果：

When you run TestApplication, it produces the following result −

C:\>java TestApplication
Moving cursor to the last...
Displaying record...
ID: 103, Age: 30, First: Sumit, Last: Mittal
Moving cursor to the first row...
Displaying record...
ID: 100, Age: 18, First: Zara, Last: Ali
Moving cursor to the next row...
Displaying record...
ID: 101, Age: 25, First: Mehnaz, Last: Fatma
C:\>