上篇展示了如何使用MyBatis执行创建操作表。本章将告诉你如何使用MyBatis来读取表。
我们已经在MySQL下有EMPLOYEE表：
1 CREATE TABLE EMPLOYEE ( 2 id INT NOT NULL auto_increment, 3 first_name VARCHAR(20) default NULL, 4 last_name VARCHAR(20) default NULL, 5 salary INT default NULL, 6 PRIMARY KEY (id) 7 );
此表有如下只有一条记录：
1 mysql> select * from EMPLOYEE; 2 +----+------------+-----------+--------+ 3 | id | first_name | last_name | salary | 4 +----+------------+-----------+--------+ 5 | 1 | Zara | Ali | 5000 | 6 +----+------------+-----------+--------+ 7 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：
1 public class Employee { 2 private int id; 3 private String first_name; 4 private String last_name; 5 private int salary; 6 7 /* Define constructors for the Employee class. */ 8 public Employee() {} 9 10 public Employee(String fname, String lname, int salary) { 11 this.first_name = fname; 12 this.last_name = lname; 13 this.salary = salary; 14 } 15 16 /* Here are the method definitions */ 17 public int getId() { 18 return id; 19 } 20 public String getFirstName() { 21 return first_name; 22 } 23 public String getLastName() { 24 return last_name; 25 } 26 public int getSalary() { 27 return salary; 28 } 29 } /* 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。
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创建Employee.xml如上所示。
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创建Employee.java如上图所示，并编译它。
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创建IbatisRead.java如上图所示，并编译它。
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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。
1 Going to read records..... 2 1 Zara Ali 5000 3 Record Reads Successfully
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