主要内容：
- 一般的连接数据库测试
- 把连接数据库的方法封装成一个类和测试
- 一个简单的插入表实例
- 查询数据实例
- 封装查询的数据库的信息
- 封装信息后的查询数据库
一.一般的数据库连接测试
1 public class TestConnection1 {
2 public static void main(String[] args) throws Exception {
3 Class.forName("com.mysql.jdbc.Driver");
4 String url="jdbc:mysql://localhost:3306/test?"//数据库url
5 + "useUnicode=true&characterEncoding=UTF8";//防止乱码
6 String user="h4";
7 String pass="111";
8 Connection conn=DriverManager.getConnection(url, user, pass);
9
10 System.out.println(conn+",成功连接数据库");
11 conn.close();
12 }
13 }
二.我们不可能每写一个处理信息功能就写一次连接，这样太麻烦，那么为了方便以后的应用，我们通常把数据库连接封装起来。
具体实现步骤如下：
1.定义变量：
private static String DRIVER_CLASS;
private static String URL;
private static String USERRNAME;
private static String PASSWORD;
2.在你建的eclipse根目录下新建一个File文件Properties；
文件内容为你定义的变量所指向的对象：
driver=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/test? useUnicode=true&characterEncoding=UTF8
user=h4
pass=111
3.构建一个Properties对象：Properties p=new Properties();
4. java.io下的类FileInputStream的方法；FileInputStream(String name) ：通过打开一个到实际文件的连接来创建一个 FileInputStream，该文件通过文件系统中的路径名 name 指定。
来获取这个文件里面的资料：FileInputStream fis=new FileInputStream("db.properties");
5. 用3构建的变量p来下载资料：p.load(fis);
6.利用getProperty();获取参数：
DRIVER_CLASS=p.getProperty("driver");
URL=p.getProperty("url");
USERRNAME=p.getProperty("user");
PASSWORD=p.getProperty("pass");
7.写一个连接数据库的方法getConection()；
8.写一个关闭数据库的方法close(Connection conn)；
写好后代码如下：
1 public class jdbcutil {
2 private static String DRIVER_CLASS;
3 private static String URL;
4 private static String USERRNAME;
5 private static String PASSWORD;
6 private static Properties p=new Properties();
7 static{
8 try {
9 FileInputStream fis=new FileInputStream("db.properties");
10 p.load(fis);
11 DRIVER_CLASS=p.getProperty("driver");
12 URL=p.getProperty("url");
13 USERRNAME=p.getProperty("user");
14 PASSWORD=p.getProperty("pass");
15 Class.forName(DRIVER_CLASS);
16 fis.close();
17 } catch (IOException e) {
18 e.printStackTrace();
19 } catch (ClassNotFoundException e) {
20 e.printStackTrace();
21 }
22 }
23 public static Connection getConection(){
24 Connection conn=null;
25 try{
26 conn=DriverManager.getConnection(URL, USERRNAME, PASSWORD);
27 }
28 catch (Exception e) {
29 e.printStackTrace();
30 }
31 return conn;
32 }
33 public static void close(Connection conn) {
34 try {
35 if (conn != null)
36 conn.close();
37 } catch (Exception e) {
38 e.printStackTrace();
39 }
40 }
41
42 }
那么封装好之后，我们来写一个测试类，测试连接
1 public class TestConnection2 {
2
3 public static void main(String[] args) throws Exception {
4 Connection conn=jdbcutil.getConection();//利用封装好的类名来调用连接方法便可
5 System.out.println(conn+",成功连接数据库");
6 jdbcutil.close( conn);//同样利用类名调用关闭方法即可
7 }
8 }
三.连接成功，我们写一个简单的向数据库插入表的实例。
1 public class TestDDl {
2
3 public static void main(String[] args) {
4 Connection conn=null;
5 Statement stmt=null;
6 conn=jdbcutil.getConection();//连接数据库
7 String createTableSql= " create table user_test1( "+//记住引号和单词间一定要有空格
8 " id int, "+
9 " name varchar(32) , "+
10 " password varchar(32) , "+
11 " birthday date "+
12 " ) ";
13 try {
14 stmt=conn.createStatement();
15 stmt.execute(createTableSql);
16 } catch (SQLException e) {
17 e.printStackTrace();
18 }
19 jdbcutil.close(null, stmt, conn);//关闭数据库
20 }
21 }
四.我们在写一个查询数据库数据的实例。(有三种方法)
1 public class TestDQL {
2 public static void main(String[] args){
3 Connection conn=null;//定义为空值
4 Statement stmt=null;
5 ResultSet rs=null;
6 String sql="select * from employees";//sql语句
7 conn=jdbcutil.getConection();
8 try {
9 stmt=conn.createStatement();//创建一个Statement语句对象
10 rs=stmt.executeQuery(sql);//执行sql语句
11 while(rs.next()){
12 System.out.print(rs.getInt(1)+",");
13 System.out.print(rs.getString(2)+",");//直接使用参数
14 System.out.print(rs.getString(3)+",");
15 System.out.print(rs.getString(4)+",");
16 System.out.println(rs.getString(5));
17 }
18 } catch (SQLException e) {
19 e.printStackTrace();
20 }finally{
21 jdbcutil.close(rs,stmt,conn);//关闭数据库
22 }
23 }
24 } //第二种方法如下：
1 public class TestDQl2 {
2
3 public static void main(String[] args) {
4 Connection conn=null;
5 Statement stmt=null;
6 ResultSet rs=null;
7 String sql="select * from employees";
8 conn=jdbcutil.getConection();
9 try {
10 stmt=conn.createStatement();
11 rs=stmt.executeQuery(sql);
12 while(rs.next()){
13 System.out.print(rs.getInt("userid")+",");//里面直接写要查找的内容名称
14 System.out.print(rs.getString("employee_id")+",");
15 System.out.print(rs.getString("last_name")+",");
16 System.out.print(rs.getString("salary")+",");
17 System.out.println(rs.getString("department_id"));
18 }
19 } catch (SQLException e) {
20 e.printStackTrace();
21 }finally{
22 jdbcutil.close(rs,stmt,conn);
23 }
24 }
25 }
1 //第三种方法如下：
2 public class TestDQL3 {
3 public static void main(String[] args) {
4 Connection conn=null;
5 Statement stmt=null;
6 ResultSet rs=null;
7 String sql="select * from employees";
8 conn=jdbcutil.getConection();
9 try {
10 stmt=conn.createStatement();
11 rs=stmt.executeQuery(sql);
12 while(rs.next()){
13 int index=1;
14 System.out.print(rs.getInt(index++)+",");
15 System.out.print(rs.getString(index++)+",");
16 System.out.print(rs.getString(index++)+",");
17 System.out.print(rs.getString(index++)+",");
18 System.out.println(rs.getString(index++));
19 }
20 } catch (SQLException e) {
21 e.printStackTrace();
22 }finally{
23 jdbcutil.close(rs,stmt,conn);
24 }
25 }
26 }
五.在四里面我们写了查询员工资料的信息，但是有的时候我们要保存起来方便之后更好的查找，那怎么办呢？没错，封装。
1 public class employees implements Serializable {
2 private Integer userid;
3 private String employee_id;
4 private String last_name;
5 private String salary;
6 private String department_id;
7
8 public employees() {
9 super();
10 }
11
12 public employees(String employee_id, String last_name, String salary, String department_id) {
13 super();
14 this.employee_id = employee_id;
15 this.last_name = last_name;
16 this.salary = salary;
17 this.department_id = department_id;
18 }
19
20 @Override
21 public String toString() {
22 return "employees [userid=" + userid + ", employee_id=" + employee_id + ", last_name=" + last_name
23 + ", salary=" + salary + ", department_id=" + department_id + "]";
24 }
25
26 public Integer getUserid() {
27 return userid;
28 }
29
30 public void setUserid(Integer userid) {
31 this.userid = userid;
32 }
33
34 public String getEmployee_id() {
35 return employee_id;
36 }
37
38 public void setEmployee_id(String employee_id) {
39 this.employee_id = employee_id;
40 }
41
42 public String getLast_name() {
43 return last_name;
44 }
45
46 public void setLast_name(String last_name) {
47 this.last_name = last_name;
48 }
49
50 public String getSalary() {
51 return salary;
52 }
53
54 public void setSalary(String salary) {
55 this.salary = salary;
56 }
57
58 public String getDepartment_id() {
59 return department_id;
60 }
61
62 public void setDepartment_id(String department_id) {
63 this.department_id = department_id;
64 }
65 }
六.封装好后的查询和上面没封装之前有点变化。
1 public class TestDQL4 {
2 public static void main(String[] args) {
3 Connection conn=null;
4 Statement stmt=null;
5 ResultSet rs=null;
6 List<employees> emps=new ArrayList<>();//构造集合对象
7
8 String sql="select * from employees";
9
10 conn=jdbcutil.getConection();//获取数据库连接
11
12 try {
13 stmt=conn.createStatement();
14 rs=stmt.executeQuery(sql);
15 while(rs.next()){//遍历结果集
16 int index=1;
17 employees emp=new employees();//构造员工类对象
18 emp.setUserid(rs.getInt(index++));//获取值
19 emp.setEmployee_id(rs.getString(index++));
20 emp.setLast_name(rs.getString(index++));
21 emp.setSalary(rs.getString(index++));
22 emp.setDepartment_id(rs.getString(index++));
23 emps.add(emp);//放到集合中去
24 }
25 } catch (SQLException e) {
26 e.printStackTrace();
27 }finally{
28 jdbcutil.close(rs,stmt,conn);//关闭连接
29 }
30 for(employees emp:emps){//遍历
31 System.out.println(emp);
32 }
33 }
34 }
其实我们可以继续封装，把遍历结果集给封装起来。
1 public class TestDQL5 {
2
3 public static void main(String[] args) {
4 Connection conn=null;
5 Statement stmt=null;
6 ResultSet rs=null;
7 List<employees> emps=new ArrayList<>();
8
9 String sql="select * from employees";
10
11 conn=jdbcutil.getConection();
12
13 try {
14 stmt=conn.createStatement();
15 rs=stmt.executeQuery(sql);
16 emps=resultSetToEmployees(rs);
17 } catch (SQLException e) {
18 e.printStackTrace();
19 }finally{
20 jdbcutil.close(rs,stmt,conn);
21 }
22 for(employees emp:emps){
23 System.out.println(emp);
24 }
25 }
26 public static List<employees> resultSetToEmployees(ResultSet rs){
27 List<employees> emps=new ArrayList<>();
28 try {
29 while(rs.next()){
30 int index=1;
31 employees emp=new employees();
32 emp.setUserid(rs.getInt(index++));
33 emp.setEmployee_id(rs.getString(index++));
34 emp.setLast_name(rs.getString(index++));
35 emp.setSalary(rs.getString(index++));
36 emp.setDepartment_id(rs.getString(index++));
37 emps.add(emp);
38 }
39 } catch (SQLException e) {
40 e.printStackTrace();
41 }
42
43 return emps;
44 }
45 }
如果是一个人查询信息呢？还可以这样封装。
1 public class TestDQL6 {
2 public static void main(String[] args) {
3 Connection conn=null;
4 Statement stmt=null;
5 ResultSet rs=null;
6 List<employees> emps=new ArrayList<>();
7
8 String sql="select * from employees";
9
10 conn=jdbcutil.getConection();
11
12 try {
13 stmt=conn.createStatement();
14 rs=stmt.executeQuery(sql);
15 while(rs.next()){
16 employees emp=resultSetToEmployee(rs);
17 emps.add(emp);
18 }
19 } catch (SQLException e) {
20 e.printStackTrace();
21 }finally{
22 jdbcutil.close(rs,stmt,conn);
23 }
24 for(employees emp:emps){
25 System.out.println(emp);
26 }
27 }
28 public static employees resultSetToEmployee(ResultSet rs){
29 employees emp=null;
30 try {
31 int index=1;
32 emp=new employees();
33 emp.setUserid(rs.getInt(index++));
34 emp.setEmployee_id(rs.getString(index++));
35 emp.setLast_name(rs.getString(index++));
36 emp.setSalary(rs.getString(index++));
37 emp.setDepartment_id(rs.getString(index++));
38 } catch (SQLException e) {
39 e.printStackTrace();
40 }
41 return emp;
42 }
43
时间： 2024-10-05 13:58:30