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JDBC连接数据库方法的封装，以及查询数据方法的封装

(在上一篇文章中，我们详细的介绍了连接数据库的方法，以及eclipse操作数据库信息的相关方法，在这里我们将主要讲封装。)

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     }

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原文地址：https://www.cnblogs.com/wuziyue/p/4846602.html