上一章展示了如何使用iBATIS执行创建操作表。本章将告诉你如何使用iBATIS来读取表。

我们已经在MySQL下有EMPLOYEE表：

CREATE TABLE EMPLOYEE (
   id INT NOT NULL auto_increment,
   first_name VARCHAR(20) default NULL,
   last_name  VARCHAR(20) default NULL,
   salary     INT  default NULL,
   PRIMARY KEY (id)
);

此表有如下只有一条记录：

mysql> select * from EMPLOYEE;
+----+------------+-----------+--------+
| id | first_name | last_name | salary |
+----+------------+-----------+--------+
|  1 | Zara       | Ali       |   5000 |
+----+------------+-----------+--------+
1 row in set (0.00 sec)

Employee POJO 类:

要执行读操作，我们将修改Employee类中Employee.java文件，如下所示：

public class Employee {
  private int id;
  private String first_name; 
  private String last_name;   
  private int salary;  

  /* Define constructors for the Employee class. */
  public Employee() {}
  
  public Employee(String fname, String lname, int salary) {
    this.first_name = fname;
    this.last_name = lname;
    this.salary = salary;
  }

  /* Here are the method definitions */
  public int getId() {
    return id;
  }
  public String getFirstName() {
    return first_name;
  }
  public String getLastName() {
    return last_name;
  }
  public int getSalary() {
    return salary;
  }
} /* End of Employee */

Employee.xml 文件:

要定义使用iBATIS SQL映射语句，我们将增加<select>标记在Employee.xml文件，这个标签定义中，我们会定义将用于在IbatisRead.java文件的数据库执行SQL SELECT查询的“id”。

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE sqlMap 
PUBLIC "-//ibatis.apache.org//DTD SQL Map 2.0//EN"
"http://ibatis.apache.org/dtd/sql-map-2.dtd">

<sqlMap namespace="Employee">
<insert id="insert" parameterClass="Employee">
   INSERT INTO EMPLOYEE(first_name, last_name, salary)
   values (#first_name#, #last_name#, #salary#)

   <selectKey resultClass="int" keyProperty="id">
      select last_insert_id() as id
   </selectKey>

</insert>
<select id="getAll" resultClass="Employee">
   SELECT * FROM EMPLOYEE
</select>
</sqlMap>

在这里，我们没有使用WHERE子句和SQL SELECT语句。后续章节将演示如何用WHERE和SELECT语句子句，以及如何将值传递到WHERE子句。

IbatisRead.java 文件:

该文件将应用程序级别的逻辑从雇员Employee表中读出记录：

import com.ibatis.common.resources.Resources;
import com.ibatis.sqlmap.client.SqlMapClient;
import com.ibatis.sqlmap.client.SqlMapClientBuilder;
import java.io.*;
import java.sql.SQLException;
import java.util.*;

public class IbatisRead{
  public static void main(String[] args)
   throws IOException,SQLException{
   Reader rd = Resources.getResourceAsReader("SqlMapConfig.xml");
   SqlMapClient smc = SqlMapClientBuilder.buildSqlMapClient(rd);

   /* This would read all records from the Employee table. */
   System.out.println("Going to read records.....");
   List <Employee> ems = (List<Employee>)
                        smc.queryForList("Employee.getAll", null);
   Employee em = null;
   for (Employee e : ems) {
      System.out.print("  " + e.getId());
      System.out.print("  " + e.getFirstName());
      System.out.print("  " + e.getLastName());
      System.out.print("  " + e.getSalary());
      em = e; 
      System.out.println("");
   }    

   System.out.println("Records Read Successfully ");

  }
} 

编译和运行：

下面是步骤来编译并运行上述应用。请确保您已在进行的编译和执行之前，适当地设置PATH和CLASSPATH。

• 创建Employee.xml如上所示。

• 创建Employee.java如上图所示，并编译它。

• 创建IbatisRead.java如上图所示，并编译它。

• 执行IbatisRead二进制文件来运行程序。

你会得到下面的结果，并且将记录从EMPLOYEE表中读取。

Going to read records.....
  1  Zara  Ali  5000
Record Reads Successfully

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