Here I will adopt mybatis3.2 Make database persistent , Many of them may stay under the guidance of their teachers , Still stuck with traditional JDBC Persistent access data layer . today , Let's talk about interface oriented programming and how to take advantage of annotations !

realization DAO Persistent layer

From the current Java Frame trend ,spring Framework still dominates , No matter what you use SSH Framework and SSM Framework development , Must be thorough spring There's nothing wrong with it .

From the current distribution of Internet companies , Small and medium-sized companies still own half of the country , They don't have a lot of money and development resources , In other words, very few companies use it hibernate+struts Development project , For small and medium-sized companies, the development of super large projects is beyond their consideration . that ,mybatis+springmvc Development framework is rising …

End of chat , Let me talk about the principle first :

use mybatis Define interface complete sql Statement mapping , The interface can also be directly used as DAO Use of components of .

Bridge mode, you know ?

Application of bridge mode here :

Using this pattern can embody business logic component encapsulation DAO Patterns of components , You can also separate business logic components from DAO Functions of components . in other words , Business logic components are responsible for changes in business logic , and DAO Components are responsible for persistent changes .

Benefits of doing so :
① each DAO Component contains the access logic of the database .
② each DAO Component can complete basic CRUD Etc .

1. Common constant class

HrmConstants class

1234567891011121314151617181920212223/** *  * constant  * */public class HrmConstants
{     // Database table constant     public static final String USERTABLE="user_inf";    public
static final String DEPTTABLE="dept_inf";    public static final String
JOBTABLE="job_inf";    public static final String EMPLOYEETABLE="employee_inf";
    public static final String NOTICETABLE="notice_inf";    public static final
String DOCUMENTTABLE="document_inf";         // Sign in     public static final String
LOGIN="loginFrom";    // User's session object     public static final String USER_SESSION=
"user_session";    // Default per page 4 Data     public static int PAGE_DEFAULT_SIZE=4;     }

I won't post the database here . This common constant class is defined according to the structure of the database table , That is to say, in the database, I created 6 Tables , Each table corresponds to this class one by one . As for here session object , It is for the later stage of writing control layer , Nothing to do with what I've said .

2. Entity class

4546474849505152535455565758596061626364656667/** *  * User entity class  * */public class
User {     private Integer id;//id    private String username;// user name     private
String loginname;// Login name     private String password;// password     private Integer
status;// state     private Date createDate;// created date          public User() {    }     
//setter and getter method     public Integer getId() {        return id;    }     public
void setId(Integer id) { = id;    }     public String
getUsername() {        return username;    }     public void setUsername(String
username) {        this.username = username;    }     public String
getLoginname() {        return loginname;    }     public void
setLoginname(String loginname) {        this.loginname = loginname;    }     
public String getPassword() {        return password;    }     public void
setPassword(String password) {        this.password = password;    }     public
Integer getStatus() {        return status;    }     public void
setStatus(Integer status) {        this.status = status;    }     public Date
getCreateDate() {        return createDate;    }     public void
setCreateDate(Date createDate) {        this.createDate = createDate;    }     }

here , I will make a case introduction with user entity class . The basic principle of entity class is to follow javabean rule , That is to say, public class , Private member variable and its own construction method without parameter . of course , I used it here setter and getter The method simply encapsulates it .

3. definition DAO Interface

123456789101112131415161718192021222324252627282930313233343536373839/** *  *
UserDao Interface implementation class of  * */public interface UserDao {     // Login user name and password query employee     @Select(
"select * from "+USERTABLE+" where loginname = #{loginname} and password =
#{password} ")    User selectByLoginnmameAndPassword(            @Param(
"loginname") String loginname,            @Param("password") String password
            );         // according to Id Query users     @Select("select * from "+USERTABLE+" where
id = #{id} ")    User selectById(Integer id);         // according to Id delete user     @Delete(
"delete from "+USERTABLE+" where id = #{id} ")    void deleteById(Integer id);
         // Dynamically modify users     @SelectProvider(method = "updateUser", type =
UserDynaSqlProvider.class)    void update(User user);         // Dynamic query     
@SelectProvider(method = "selectWhitParam", type = UserDynaSqlProvider.class)
    List<User> selectByPage(Map<String, Object> params);         // Total number of users queried by parameters
    @SelectProvider(method = "count", type = UserDynaSqlProvider.class)    
Integer count(Map<String, Object> params);         // Insert users dynamically     @SelectProvider
(method ="inserUser", type = UserDynaSqlProvider.class)    void save(User user);
This is the real beginning of sublimation , First of all, I've only defined one UserDao Interface of , And then make the most of it mybatis Annotation advantage of , Defined ’ Login user name and password query employee ’ Method of ……

Here, I'd like to add some explanatory knowledge for you :

@Select annotation , Don't explain that , It is equivalent to an annotation for storing query statements , Defined on a method , The effect is equivalent to writing a query statement in the configuration file .

@Param annotation , It's an explanation of the parameters . Used here string
loginname It is defined in the public constant class . How to put it? , We can understand that request.setAttribute(“”,”") The sublimation of this form .

@SelectProvider annotation , For generating queries sql sentence , Different from @Select annotation . Structurally ,@SelectProvide Specified a Class And methods , By calling Class This method on to get sql sentence .

matters needing attention :

① there @Param Annotations are based on mybatis Framed , no spring On frame , Pay attention when importing packages !

②@SelectProvider Annotation has a span in the thinking of programming , Because it needs a class And its methods , So when defining this annotation , Be sure to think about what the classes and methods in the next hierarchy need to do ! of course , Methods in interfaces , It can be budgeted in advance , But the note on it , You have to think more to make a decision !
③ Common constant class . On the application of this interface , Since it's interface oriented programming , And complete the basic operation of the database , Then it must be imported into the public constant class USERTABLE Of .
④id = #{id} Generated sql Statement is id = ?

4. dynamic SQL Provider class

858687888990public class UserDynaSqlProvider {     // Paging dynamic query     public String
selectWhitParam(final Map<String, Object> params) {        String sql=new SQL(){
            {                SELECT("*");                FROM(USERTABLE);
                if (params.get("user")!=null) {                    User
user=(User) params.get("user");                    if (user.getUsername()!=null
&& !user.getUsername().equals("")) {                        WHERE(" username
LIKE CONCAT('%',#{user.username},'%') ");                    }
                    if (user.getStatus()!=null && !user.getStatus().equals(""))
{                        WHERE(" status LIKE CONCAT('%',#{user.status},'%') ");
                    }                }            }        }.toString();        
if (params.get("pageModel")!=null) {            sql += " limit
#{pageModel.firstLimitParam} , #{pageModel.pageSize} ";        }        return
sql;    }         // Total number of dynamic queries     public String count(final Map<String, Object>
params) {        return new SQL(){            {                SELECT("*");
                FROM(USERTABLE);                if (params.get("user") !=null) {
                    User user=(User) params.get("user");                    if
(user.getUsername()!=null && !user.getUsername().equals("")) {
                        WHERE(" username LIKE CONCAT('%',#{user.username},'%') "
);                    }                    if (user.getStatus()!=null &&
!user.getStatus().equals("")) {                        WHERE(" status LIKE
CONCAT('%',#{user.status},'%') ");                    }                }
            }        }.toString();    }         // Dynamic insertion     public String
inserUser(final User user) {        return new SQL(){            {
                INSERT_INTO(USERTABLE);                if (user.getUsername()!=
null && !user.getUsername().equals("")) {                    VALUES("username",
"#{username}");                }                if (user.getStatus()!=null &&
!user.getStatus().equals("")) {                    VALUES("status", "#{status}"
);                }                if (user.getLoginname()!=null &&
!user.getLoginname().equals("")) {                    VALUES("loginname",
"#{loginname}");                }                if (user.getPassword()!=null
&& !user.getPassword().equals("")) {                    VALUES("password",
"#{password}");                }            }        }.toString();    }         
// Dynamic update     public String updateUser(final User user) {        return new SQL(){
            {                UPDATE(USERTABLE);                if
(user.getUsername()!=null) {                    SET(" username = #{username} ");
                }                if (user.getLoginname()!=null) {
                    SET(" loginname = #{loginname} ");                }
                if (user.getPassword()!=null) {                    SET("
password = #{password} ");                }                if
(user.getStatus()!=null) {                    SET(" status = #{status} ");
                }                if (user.getCreateDate()!=null) {
                    SET(" create_date = #{createDate} ");                }
                WHERE(" id = #{id} ");            }        }.toString();    }}

As I said earlier when I wrote the interface class , Now that it's used @SelectProvider annotation , It's bound to use one class And its methods . We used it four times in the interface class @SelectProvider annotation , So there are four ways to do it , Paging dynamic query (selectWhitParam), Total number of dynamic queries (count), Dynamic insertion (inserUser), Dynamic update (updateUser).

This class is specially provided for the interface sql Statement serving , No longer need to implement traditional interfaces , Using annotations instead of the original tedious things .

ps: Maybe someone will wonder , How do we configure what we write in applicationContext.xml Inside ? Will it be very troublesome ? Now? , I tell you , No trouble at all !

configuration file


12345678<!-- mybatis:scan Can scan com.dao.inter All interfaces under the package are treated as spring Of bean to configure , Dependency injection can be done later
-->    <mybatis:scan base-package="com.dao.inter"/>    <!--
use PropertyOverrideConfigurer Post processor load data source parameters -->    <context:property-override
location="" />    <!-- to configure c3p0 data source -->    <bean id=
"dataSource" class="com.mchange.v2.c3p0.CombopooledDataSource "/>    <!--
to configure yes mybatis Community development for integration Spring Of bean
-->    <bean id="sqlSessionFactory" class=
"org.mybatis.spring.SqlSessionFactoryBean" p:dataSource-ref="dataSource"/>


principle :mybatis Persistence of DAO Interface only needs to pass SqlSession Of getMapper Method to obtain the corresponding interface instance , So as to call the interface method to complete the operation of the database , And in spring In the container , Only responsible for generation and management DAO Components of .

I'm done ? So do you think it's better than traditional JDBC Persistent access is easier ? I think , At least it's more convenient .

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