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Java Mybatis framework Dao layer implementation and mapping files and core configuration file example analysis, many novices are not very clear about this, in order to help you solve this problem, the following editor will explain in detail for you, people with this need can come to learn, I hope you can get something.

The Dao layer of Mybatis implements the traditional development method

1. Write UserDao interface

Public interface UserMapper {public List findAll () throws IOException;}

2. Write UserDaoImpl implementation

3. Test the traditional way

Agent development mode

Introduction of agent development method

The agent development method of Mybatis is used to realize the development of DAO layer, which is the mainstream for us to enter the enterprise.

The Mapper interface development method only needs the programmer to write the Mapper interface (equivalent to the Dao interface), and the Mybatis framework creates the dynamic proxy object of the interface according to the interface definition, and the method body of the proxy object is the same as the above Dao interface implementation class method.

Mapper interface development needs to follow the following specifications:

The namespace in the ① Mapper.xml file has the same fully qualified name as the mapper interface

The ② Mapper interface method name is the same as the id for each statement defined in Mapper.xml

The input parameter type of the ③ Mapper interface method is the same as the parameterType type of each sql defined in mapper.xml. 4. The output parameter type of the ④ Mapper interface method is the same as the resultType type of each sql defined in mapper.xml.

With

1. Write UserMapper interface

2. Test agent mode

MyBatis mapping file goes deep into dynamic sql statements

Dynamic sql statement description [official documentation]

Dynamic SQL

We use different SQL statements to query according to the different values of the entity class. For example, if the id is not empty, you can query according to id, and add the user name as a condition if the username is different. This situation is often encountered in our multi-conditional combination queries.

Select * from user and id=# {id} and username=# {username} and password=# {password}

When the query conditions id and username exist, the test code is as follows

Dynamic SQL

The loop performs the stitching operation of sql, for example: SELECT * FROM USER WHERE id IN (1 ~ 2 ~ 5).

# {id}

The test code is as follows

The attribute meaning of the foreach tag is as follows:

The tag is used to traverse the collection, and its properties are:

① collection: represents the collection element to be traversed. Be careful not to write # {} when writing

② open: represents the beginning of the statement

③ close: represents the closing section

④ item: represents the name of the generated variable for each element of the traversal collection

⑤ sperator: represents the delimiter

SQL fragment extraction

The duplicate sql can be extracted from Sql and can be referenced by include when using it, so as to achieve the purpose of sql reuse.

Summary

MyBatis mapping file configuration:

Query

: insert

: modify

: deletin

Where condition

If judgment

: cycle

Sql fragment extraction

The Mybatis core profile goes deep into the typeHandlers tag

Whether MyBatis sets a parameter in a preprocessing statement (PreparedStatement) or fetches a value from the result set, the type handler converts the acquired value to the Java type in an appropriate manner. The following table describes some of the default type handlers (intercept section).

You can override type handlers or create your own type handlers to handle unsupported or non-standard types. To do this: implement the org.apache.ibatis.type.TypeHandler interface, or inherit a convenient class, org.apache.ibatis.type.BaseTypeHandler, and optionally map it to a JDBC type. For example, the requirement: a Date data type in Java, which I want to save to a database in milliseconds from 1970 to the present, and when taken out, it is converted to the Date of java, that is, the conversion between the Date of java and the Varchar millisecond value of the database.

Development steps:

① defines the transformation class inheritance class BaseTypeHandler

② covers four unimplemented methods, in which setNonNullarameter sets the callback method of data to the database for the java program, and getNullableResult is the method for converting the string type of mysql to the Type type of java when querying.

③ registers in the MyBatis core configuration file

④ tests whether the conversion is correct

Public class DateTypeHandler extends BaseTypeHandler {/ / convert the java type to the type required by the database public void setNonNullParameter (PreparedStatement preparedStatement, int I, Date date, JdbcType jdbcType) throws SQLException {long time = date.getTime (); preparedStatement.setLong (iQuery time) } / / convert the type in the database to java type / / the field name to be converted by the String parameter / / the result set queried by ResultSet public Date getNullableResult (ResultSet resultSet, String s) throws SQLException {/ / get the data needed in the result set (long) convert to Date type return long aLong = resultSet.getLong (s); Date date = new Date (aLong); return date } / / convert types in the database to java types public Date getNullableResult (ResultSet resultSet, int I) throws SQLException {long aLong = resultSet.getLong (I); Date date = new Date (aLong); return date;} / / convert types in the database to java types public Date getNullableResult (CallableStatement callableStatement, int I) throws SQLException {long aLong = callableStatement.getLong (I) Date date = new Date (aLong); return date;}}

Test add operation

Database data:

Plugins tag

MyBatis can use third-party plug-ins to expand the function. The paging assistant PageHelper encapsulates the complex operation of paging and uses a simple way to obtain the relevant data of paging.

Development steps:

① imports coordinates of generic PageHelper

② configures the PageHelper plug-in in the mybatis core configuration file

③ test paging data acquisition

① imports coordinates of generic PageHelper

Com.github.pagehelper pagehelper 3.7.5 com.github.jsqlparser jsqlparser 0.9.1

② configures the PageHelper plug-in in the mybatis core configuration file

③ test paging data acquisition

Get other parameters related to paging

/ / get the parameters related to paging PageInfo pageInfo = new PageInfo (userList); System.out.println ("current page:" + pageInfo.getPageNum ()); System.out.println ("number of entries per page:" + pageInfo.getPageSize ()); System.out.println ("total number of pages:" + pageInfo.getTotal ()); System.out.println ("total pages:" + pageInfo.getPages ()) System.out.println ("previous page:" + pageInfo.getPrePage ()); System.out.println ("next page:" + pageInfo.getNextPage ()); System.out.println ("whether it is the first:" + pageInfo.isIsFirstPage ()); System.out.println ("is it the last:" + pageInfo.isIsLastPage ()); summary

Common tags for MyBatis core configuration files:

1. Properties tag: this tag can load external properties files

2. TypeAliases tag: set type alias

3. Environments tag: data source environment configuration label

4. TypeHandlers tag: configure custom type handlers

5. Plugins tag: configure the plug-in for MyBatis

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