It's enough for MyBatis to explain in detail

Chapter 1 details of MyBatis framework configuration file

1.1 typeHandlers type converter

Whenever MyBatis sets the parameter to PreparedStatement or gets the value from the ResultSet result set, TypeHandler is used to handle the conversion between database type and java type. The following table describes the default

TypeHandlers

1.1.1 custom type converter

Suppose that the field in the table is of type int, and the attribute corresponding to the entity class is of type boolean, then the user-defined type converter can be used for correspondence.

(1) entity class

 1 package com.chenyanbin.beans;
 2 
 3 public class Dept {
 4     private Integer deptNo;
 5     private String dname;
 6     private String loc;
 7     private boolean flag;
 8     public Integer getDeptNo() {
 9         return deptNo;
10     }
11     public boolean isFlag() {
12         return flag;
13     }
14     public void setFlag(boolean flag) {
15         this.flag = flag;
16     }
17     public void setDeptNo(Integer deptNo) {
18         this.deptNo = deptNo;
19     }
20     public String getDname() {
21         return dname;
22     }
23     public void setDname(String dname) {
24         this.dname = dname;
25     }
26     public String getLoc() {
27         return loc;
28     }
29     public void setLoc(String loc) {
30         this.loc = loc;
31     }
32 }

(2) fields in the table

(3) develop custom type converter: MyTypeHandler.java

Inherit and implement interface: TypeHandler.java

 1 package com.chenyanbin.util;
 2 
 3 import java.sql.CallableStatement;
 4 import java.sql.PreparedStatement;
 5 import java.sql.ResultSet;
 6 import java.sql.SQLException;
 7 
 8 import org.apache.ibatis.jdbc.Null;
 9 import org.apache.ibatis.type.JdbcType;
10 import org.apache.ibatis.type.TypeHandler;
11 /*
12  * setParameter:This method is called only when generating SQL statements
13  * 
14  * getResult:When converting a ResultSet data row to an entity class object after the query, inform the TypeHandler what type to convert a field in the current data row
15  * 
16  * 
17  */
18 public class MyTypeHandler implements TypeHandler {
19 
20     public void setParameter(PreparedStatement ps, int i, Object parameter, JdbcType jdbcType) throws SQLException {
21         if (parameter==null) { //dept.flag=null insertsql flag setting 0
22             ps.setInt(i, 0);
23             return;
24         }
25         Boolean flag=(Boolean)parameter;
26         if (flag==true) {
27             ps.setInt(i, 1);
28         }
29         else {
30             ps.setInt(i, 0);
31         }
32     }
33 
34     public Object getResult(ResultSet rs, String columnName) throws SQLException {
35         int flag = rs.getInt(columnName); //1 or 0
36         Boolean myFlag=Boolean.FALSE;
37         if (flag==1) {
38             myFlag=Boolean.TRUE;
39         }
40         return myFlag;
41     }
42 
43     public Object getResult(ResultSet rs, int columnIndex) throws SQLException {
44         // TODO Auto-generated method stub
45         return null;
46     }
47 
48     public Object getResult(CallableStatement cs, int columnIndex) throws SQLException {
49         // TODO Auto-generated method stub
50         return null;
51     }
52 
53 }

(4) register the custom type converter in MyBatis core configuration file:

myBatis-config.xml

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <!DOCTYPE configuration
 3   PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
 4   "http://mybatis.org/dtd/mybatis-3-config.dtd">
 5 <configuration>
 6     <!-- Attribute configuration -->
 7     <properties resource="config.properties"></properties>
 8     <!-- Alias configuration -->
 9     <typeAliases>
10         <package name="com.chenyanbin.beans" />
11         <package name="com.chenyanbin.dao" />
12     </typeAliases>
13     <!-- Type processor -->
14     <typeHandlers>
15         <!-- from java Medium Boolean turn jdbc Medium NUMERIC -->
16         <typeHandler handler="com.chenyanbin.util.MyTypeHandler"
17             javaType="Boolean" jdbcType="NUMERIC" />
18     </typeHandlers>
19     <!-- Environmental configuration -->
20     <environments default="development">
21         <!-- Environmental configuration -->
22         <environment id="development">
23             <!-- Transaction manager -->
24             <transactionManager type="JDBC"></transactionManager>
25             <!-- data source -->
26             <dataSource type="pooled">
27                 <property name="driver" value="${jdbc.driver}" />
28                 <property name="url" value="${jdbc.url}" />
29                 <property name="username" value="${jdbc.username}" />
30                 <property name="password" value="${jdbc.password}" />
31             </dataSource>
32         </environment>
33     </environments>
34     <!-- Mapper -->
35     <mappers>
36         <package name="com.chenyanbin.dao" />
37     </mappers>
38 </configuration>

config.properties

1 jdbc.driver=com.mysql.jdbc.Driver
2 jdbc.url=jdbc:mysql://localhost:3306/sam
3 jdbc.username=root
4 jdbc.password=root

(5) create interface: DeptMapper.java

 1 package com.chenyanbin.dao;
 2 
 3 import java.util.List;
 4 import com.chenyanbin.beans.Dept;
 5 
 6 public interface DeptMapper {
 7     public void deptSave(Dept dept);
 8 
 9     public List<Dept> deptFind();
10 }

(6) DeptMapper.xml

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <!DOCTYPE mapper
 3   PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
 4   "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
 5 <mapper namespace="com.chenyanbin.dao.DeptMapper">
 6     <insert id="deptSave">
 7         insert into dept (DEPTNO,DNAME,LOC,flag)
 8         values(#{deptNo},#{dname},#{loc},#{flag})
 9     </insert>
10     <select id="deptFind" resultType="Dept">
11         select deptNo,dname,loc,flag from dept
12     </select>
13 </mapper>

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <!DOCTYPE configuration
 3   PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
 4   "http://mybatis.org/dtd/mybatis-3-config.dtd">
 5 <configuration>
 6     <!-- Attribute configuration -->
 7     <properties resource="config.properties"></properties>
 8     <!-- Alias configuration -->
 9     <typeAliases>
10         <package name="com.chenyanbin.beans" />
11         <package name="com.chenyanbin.dao" />
12     </typeAliases>
13     <!-- Environmental configuration -->
14     <environments default="development">
15         <!-- Environmental configuration -->
16         <environment id="development">
17             <!-- Transaction Manager -->
18             <transactionManager type="JDBC"></transactionManager>
19             <!-- data source -->
20             <dataSource type="pooled">
21                 <property name="driver" value="${jdbc.driver}" />
22                 <property name="url" value="${jdbc.url}" />
23                 <property name="username" value="${jdbc.username}" />
24                 <property name="password" value="${jdbc.password}" />
25             </dataSource>
26         </environment>
27     </environments>
28     <!-- Mapper -->
29     <mappers>
30         <package name="com.chenyanbin.dao" />
31     </mappers>
32 </configuration>

Mode 2: myBatis-config.xml

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <!DOCTYPE mapper
 3   PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
 4   "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
 5 <mapper namespace="com.chenyanbin.dao.DeptMapper">
 6     <insert id="deptSave">
 7         insert into dept (DEPTNO,DNAME,LOC,flag)
 8         values(#{deptNo},#{dname},#{loc},#{flag})
 9     </insert>
10     <resultMap type="dept" id="deptMap">
11     <result column="flag" property="flag" typeHandler="com.chenyanbin.util.MyTypeHandler"/>
12     </resultMap>
13     <select id="deptFind" resultType="Dept">
14         select deptNo,dname,loc,flag from dept
15     </select>
16 </mapper>

Mode 2: DeptMapper.xml

1.2 objectFactory

Every time MyBatis creates a new instance of the resulting object, it uses an object factory instance to do so. The default object factory only needs to instantiate the target class, either through the default constructor or through the parameter constructor when the parameter mapping exists. If you want to override the default behavior of an object factory, you can do so by creating your own object factory.

1.2.1 custom object factory

1.3 Plugins interceptor

One of the functions of interceptors is that we can intercept the calls of some methods. We can choose to add some logic before and after the execution of these intercepted methods, or we can execute our own logic when executing these intercepted methods instead of the intercepted methods. One of the original intention of Mybatis interceptor design is for users to realize their own logic at some time without having to move the inherent logic of Mybatis. For example, for the Executor, there are several implementations in Mybatis: BatchExecutor, reuseexecution, simpleexecution, and cachexecution. At this time, if you think the query methods of these implementations for the Executor interface can't meet your requirements, what should you do? Do you want to change the source code? Of course not. We can set up a query method for the Mybatis interceptor to intercept the Executor interface. After intercepting, we can implement our own query method logic, and then we can choose whether to continue to execute the original query method or not.

Mybatis provides us with an Interceptor interface, through which we can define our own interceptors. Let's first look at the definition of this interface:

We can see that there are three methods defined in the interface, intercept, plugin and setProperties. The plugin method is used by the interceptor to encapsulate the target object. Through this method, we can return the target object itself or its agent. When the returned method is an agent, we can intercept the methods to call the intercept method, and of course, we can call other methods, which will be explained later. The setProperties method is used to specify some properties in the Mybatis configuration file.

The most important thing to define your own Interceptor is to implement the plugin method and intercept method. In the plugin method, we can decide whether to intercept and then decide what kind of target object to return. The intercept method is the method to be executed when intercepting.

For the plugin method, mybatis has provided us with an implementation. Mybatis has a class called plugin, which has a static method wrap(Object target,Interceptor interceptor), through which you can decide whether the object to be returned is the target object or the corresponding agent.

There are two important annotations for implementing your own Interceptor. One is @ intercepts, whose value is an array of @ Signature. @Intercepts indicates that the current object is an Interceptor, while @ Signature indicates the interface, method and corresponding parameter type to be intercepted.

Programmer Group

It's enough for MyBatis to explain in detail

Chapter 1 details of MyBatis framework configuration file

1.1 typeHandlers type converter

1.1.1 custom type converter

1.2 objectFactory

1.2.1 custom object factory

1.3 Plugins interceptor

Chapter 2 Mapper configuration file details of MyBatis framework

2.1 parameter ({parameter name})

2.2 difference between {} and ${}

2.3 resultMap

2.4 Sql tag

Chapter 3: MyBatis dynamic SQL

3.1 what is MyBatis dynamic SQL

3.2 dynamic SQL dependency label

if use

choose,when,otherwise

Use of when

set use

trim use

Use of foreach

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