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：
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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