Mybatis BASICS (3) ---- SqlMapConfig. xml global configuration file parsing, mybatis getting started tutorial

Mybatis BASICS (3) ---- SqlMapConfig. xml global configuration file parsing, mybatis getting started tutorial
I. Content and configuration SEQUENCE OF THE SqlMapConfig. xml configuration file are as follows:

Mappers)

Ii. properties

Purpose: separately configure the data connection in the db. properties, only need to be in SqlMapConfig. load db in xml. properties attribute value in SqlMapConfig. in xml, you do not need to hard encode the database connection parameters. Database Connection parameters are only configured in db. properties to facilitate unified management of parameters. Other xml can reference this db. properties.

Content of db. properties:

jdbc.driver=com.mysql.jdbc.Driverjdbc.url=jdbc:mysql://localhost:3306/mybatisjdbc.username=rootjdbc.password=root

Load db. properties in SqlMapConfig. xml

<! -- Load database file db. properties -->
<Properties resource = "db. properties"> <! -- Properties can also be configured with some attribute names and attribute values. Here, the attribute values are preferentially loaded --> <! -- <Property name = "driver" value = ""/> --> </properties> <! -- After integration with spring, environments configuration will be abolished --> <environments default = "development"> <environment id = "development"> <! -- Use jdbc transaction management, and the transaction control is managed by mybatis --> <transactionManager type = "JDBC"/> <! -- Database connection pool, managed by mybatis --> <dataSource type = "POOLED"> <property name = "driver" value = "$ {jdbc. driver} "/> <property name =" url "value =" $ {jdbc. url} "/> <property name =" username "value =" $ {jdbc. username} "/> <property name =" password "value =" $ {jdbc. password} "/> </dataSource> </environment> </environments>

Properties features:

Note:

• Properties defined in the properties element are read first.
• Then, read the properties loaded by resource or url in the properties element, which overwrites the read attributes of the same name.
• Finally, read the properties passed by parameterType, which overwrites the read attributes of the same name.

Suggestion:

Do not add any attribute values to the properties element. Only the attribute values are defined in the properties file.

Attribute names defined in the properties file must have some special characteristics, such as xxxx. xxxx (jdbc. driver)

Iii. settings global parameter configuration

You can adjust some running parameters when running the mybatis framework. For example, enable Level 2 Cache and enable delayed loading. Global parameters affect the running behavior of mybatis.

Configuration attributes and descriptions of mybatis-settings

Setting)	Description)	Valid Values (Verification value group)	Default (Default)
CacheEnabled	Enable or disable cache configuration globally for any er under this configuration.	True | false	TRUE
LazyLoadingEnabled	Enable or disable delayed loading globally. When disabled, all associated hot loads.	True | false	TRUE
AggressiveLazyLoading	When it is enabled, objects with delayed loading attributes will be fully loaded and then call any lazy attributes. Otherwise, each attribute is loaded as needed.	True | false	TRUE
MultipleResultSetsEnabled	Allow or disallow multiple result sets to be returned from a separate statement (requiring a compatible driver.	True | false	TRUE
UseColumnLabel	Use column labels instead of column names. In this regard, different drivers have different behaviors. Refer to the driver document or test two methods to determine how your driver acts.	True | false	TRUE
UseGeneratedKeys	Allows JDBC to support generated keys. Compatible drivers are required. This setting forces the generated key to be used. If it is set to true, some drivers will not be compatible, but will still work.	True | false	FALSE
AutoMappingBehavior	Specifies how MyBatis automatically maps columns to fields/attributes. NONE automatic ing. PARTIAL only automatically maps results without nested result ing definitions. FULL will automatically map the results to any complex (including nesting or other ).	NONE, PARTIAL, FULL	PARTIAL
DefaultExecutorType	Configure the default executor. SIMPLE executors do have nothing special. REUSE the executor to REUSE prepared statements. BATCH executor reuse statement and BATCH update.	SIMPLE, REUSE, BATCH	SIMPLE
SafeRowBoundsEnabled	The nested statement RowBounds is allowed.	True | false	FALSE
MapUnderscoreToCamelCase	Enable Automatic ing from the classic database column name A_COLUMN to the classic Java attribute name aColumn of the camel identity.	True | false	FALSE
Localcached	MyBatis uses the local cache to prevent loop reference and accelerate repeated nested queries. All query caches executed during a SESSION by default. If localCacheScope = STATMENT is used for statement execution, the same SqlSession is not called between two different data sharing sessions.	SESSION STATEMENT	SESSION
DbcTypeForNull	If it is null, no specific JDBC Type parameter is specified. Some drivers need to specify the JDBC Type of the column, but OTHER drivers such as NULL, VARCHAR, or OTHER work with common values.	JdbcType enumeration. Most common are: NULL, VARCHAR and OTHER	OTHER
LazyLoadTriggerMethods	Specifies the method of the object that triggers the delayed loading.	A method name list separated by commas	Equals, clone, hashCode, toString
DefaultScriptingLanguage	The specified language is generated by dynamic SQL by default.	A type alias or fully qualified class name.	Org. apache. ibatis. scripting. xmltags . XMLDynamicLanguageDriver
CallSettersOnNulls	Specify that if the setter method or map put method is used, the retrieved value is null. It is useful when you rely on Map. keySet () or null for initialization. Note that primitives (such as integer and Boolean) are not set to null.	True | false	FALSE
LogPrefix	The specified prefix string. MyBatis will add the recorder name.	Any String	Not set
LogImpl	Specify the log Implementation of MyBatis. If this setting does not exist, the record will be automatically searched.	SLF4J | LOG4J | LOG4J2 | JDK_LOGGING | COMMONS_LOGGING | STDOUT_LOGGING | NO_LOGGING	Not set
ProxyFactory	If you specify a proxy tool, MyBatis will use the object that creates the lazy loading capability.	CGLIB | JAVASSIST	CGLIB

Example of settings in the official document

<Setting name = "cacheEnabled" value = "true"/> <setting name = "lazyLoadingEnabled" value = "true"/> <setting name = "multipleResultSetsEnabled" value = "true" /> <setting name = "useColumnLabel" value = "true"/> <setting name = "useGeneratedKeys" value = "false"/> <setting name = "autoMappingBehavior" value =" PARTIAL "/> <setting name =" defaultExecutorType "value =" SIMPLE "/> <setting name =" defaultStatementTimeout "value =" 25 "/> <setting name =" safeRowBoundsEnabled "value = "false"/> <setting name = "mapUnderscoreToCamelCase" value = "false"/> <setting name = "localcached" value = "SESSION"/> <setting name = "jdbcTypeForNull "value =" OTHER "/> <setting name =" lazyLoadTriggerMethods "value =" equals, clone, hashCode, toString "/> </settings>View Code 4: typeAiases (alias)-Key Points

In mapper. xml, many statement are defined. statement requires parameterType to specify the input parameter type, and resultType to specify the ing type of the output result.

If the full path of the input type is not convenient for development when the type is specified, you can define aliases for the type specified by parameterType or resultType, and define aliases in mapper. xml to facilitate development.

4.1.mybatis default supported aliases

Alias	Ing type
_ Byte	Byte
_ Long	Long
_ Short	Short
_ Int	Int
_ Integer	Int
_ Double	Double
_ Float	Float
_ Boolean	Boolean
String	String
Byte	Byte
Long	Long
Short	Short
Int	Integer
Integer	Integer
Double	Double
Float	Float
Boolean	Boolean
Date	Date
Decimal	BigDecimal
Bigdecimal	BigDecimal

 

. Custom alias

4.2.1: define a single alias (in SqlMapConfig. xml)　　

<! -- Alias definition: defines the type: Path of the type for a single alias; alias: alias --> <typeAliases> <typeAlias type = "com. mybatis. entity. user "alias =" user "/> </typeAliases>

UserMapper. xml reference alias:

<select id="findUserById" parameterType="int" resultType="user" >    　　select * from t_user where id=#{id}</select>

　4.2.2: Define aliases in batches (frequently used)　

<! -- Batch alias definition: package: Specifies the package name. mybatis automatically scans the pojo class in the package and automatically defines the alias. the alias is the class name (either in upper or lower case) --> <typeAliases> <package name = "com. mybatis. entity "/>
<Package name = "other packages"/>
</TypeAliases>

5. typeHandlers (type processor)

In mybatis, jdbc and java types are converted using typeHandlers.

In general, the type processor provided by mybatis meets daily needs and does not need to be customized.

Mybatis supports type processors:

Type Processor	Java type	JDBC Type
BooleanTypeHandler	Boolean, boolean	Any compatible Boolean Value
ByteTypeHandler	Byte, byte	Any compatible number or byte type
ShortTypeHandler	Short, short	Any compatible number or short integer
IntegerTypeHandler	Integer, int	Any compatible number and integer type
LongTypeHandler	Long, long	Any compatible number or long integer
FloatTypeHandler	Float, float	Any compatible numeric or single precision floating point type
DoubleTypeHandler	Double, double	Any compatible numeric or Double Precision Floating Point Type
BigDecimalTypeHandler	BigDecimal	Any compatible numeric or decimal type
StringTypeHandler	String	CHAR and VARCHAR types
ClobTypeHandler	String	CLOB and LONGVARCHAR types
NStringTypeHandler	String	NVARCHAR and NCHAR types
NClobTypeHandler	String	NCLOB type
ByteArrayTypeHandler	Byte []	Any compatible byte stream type
BlobTypeHandler	Byte []	BLOB and LONGVARBINARY types
DateTypeHandler	Date (java. util)	TIMESTAMP type
DateOnlyTypeHandler	Date (java. util)	DATE type
TimeOnlyTypeHandler	Date (java. util)	TIME Type
SqlTimestampTypeHandler	Timestamp (java. SQL)	TIMESTAMP type
SqlDateTypeHandler	Date (java. SQL)	DATE type
SqlTimeTypeHandler	Time (java. SQL)	TIME Type
ObjectTypeHandler	Arbitrary	Other or unspecified types
EnumTypeHandler	Enumeration type	VARCHAR-any compatible string type that is stored as code (rather than indexed ).

6. mappers (ing configuration)

6.1: load a single ing file using resource

<! -- Load the ing file --> <mappers> <! -- Load a ing file at a time using the resource method --> <mapper resource = "sqlmap/User. xml "/> <mapper resource =" mapper/UserMapper. xml "/> </mappers>

6.2: load a single ing file through the ER interface

<! -- Use the mapper interface to load a single ing configuration file following certain specifications: you need to set the ER interface class name and mapper. the name of the xml ing file must be consistent and in a directory. The premise of the preceding rule is that the mapper proxy method is used; --> <mapper class = "com. mybatis. mapper. userMapper "/>

According to the above specifications, put mapper. java and mapper. xml in a directory with the same name.

6.3: Load mapper in batches (recommended)

<! -- Load the er configuration file in batches. mybatis automatically scans the ER interface under the package to load according to certain specifications: The mapper Interface Class Name and mapper must be set. the name of the xml ing file must be consistent and in a directory. The premise of the preceding rule is that the mapper proxy method is used; --> <package name = "com. mybatis. mapper "/>