Java的MyBatis框架中Mapper映照設置裝備擺設的應用及道理解析。本站提示廣大學習愛好者：（Java的MyBatis框架中Mapper映照設置裝備擺設的應用及道理解析）文章只能為提供參考，不一定能成為您想要的結果。以下是Java的MyBatis框架中Mapper映照設置裝備擺設的應用及道理解析正文
Mapper的內置辦法
model層就是實體類，對應數據庫的表。controller層是Servlet，重要是擔任營業模塊流程的掌握，挪用service接口的辦法，在struts2就是Action。Service層重要做邏輯斷定，Dao層是數據拜訪層，與數據庫停止對接。至於Mapper是mybtis框架的映照用到,mapper映照文件在dao層用。
上面是引見一下Mapper的內置辦法：
1、countByExample ===>依據前提查詢數目
int countByExample(UserExample example);
//上面是一個完全的案列
UserExample example = new UserExample();
Criteria criteria = example.createCriteria();
criteria.andUsernameEqualTo("joe");
int count = userDAO.countByExample(example);
相當於：select count(*) from user where username='joe'
2、deleteByExample ===>依據前提刪除多條
int deleteByExample(AccountExample example);
//上面是一個完全的案例
UserExample example = new UserExample();
Criteria criteria = example.createCriteria();
criteria.andUsernameEqualTo("joe");
userDAO.deleteByExample(example);
相當於：delete from user where username='joe'
3、deleteByPrimaryKey===>依據前提刪除單條
int deleteByPrimaryKey(Integer id); userDAO.deleteByPrimaryKey(101);
相當於：
delete from user where id=101
4、insert===>拔出數據
int insert(Account record);
//上面是完全的案例
User user = new User();
//user.setId(101);
user.setUsername("test");
user.setPassword("123456")
user.setEmail("[email protected]");
userDAO.insert(user);
相當於：
insert into user(ID,username,password,email) values(101,'test','123456','[email protected]');
5、insertSelective===>拔出數據
int insertSelective(Account record);
6、selectByExample===>依據前提查詢數據
List<Account> selectByExample(AccountExample example);
//上面是一個完全的案例
UserExample example = new UserExample();
Criteria criteria = example.createCriteria();
criteria.andUsernameEqualTo("joe");
criteria.andUsernameIsNull();
example.setOrderByClause("username asc,email desc");
List<?>list = userDAO.selectByExample(example);
相當於：select * from user where username = 'joe' and username is null order by username asc,email desc
//注：在iBator 生成的文件UserExample.java中包括一個static 的外部類 Criteria ，在Criteria中有許多辦法，重要是界說SQL 語句where後的查詢前提。
7、selectByPrimaryKey===>依據主鍵查詢數據
Account selectByPrimaryKey(Integer id);//相當於select * from user where id = 變量id
8、updateByExampleSelective===>按前提更新值不為null的字段
int updateByExampleSelective(@Param("record") Account record, @Param("example") AccountExample example);
//上面是一個完全的案列
UserExample example = new UserExample();
Criteria criteria = example.createCriteria();
criteria.andUsernameEqualTo("joe");
User user = new User();
user.setPassword("123");
userDAO.updateByPrimaryKeySelective(user,example);
相當於：update user set password='123' where username='joe'
9、updateByExampleSelective===>按前提更新
int updateByExample(@Param("record") Account record, @Param("example") AccountExample example);
10、updateByPrimaryKeySelective===>按前提更新
int updateByPrimaryKeySelective(Account record);
//上面是一個完全的案例
User user = new User();
user.setId(101);
user.setPassword("joe");
userDAO.updateByPrimaryKeySelective(user);
相當於：
update user set password='joe' where id=101
int updateByPrimaryKeySelective(Account record);
//上面是一個完全的案例
User user = new User();
user.setId(101);
user.setPassword("joe");
userDAO.updateByPrimaryKeySelective(user);
相當於：update user set password='joe' where id=101
11、updateByPrimaryKey===>按主鍵更新
int updateByPrimaryKey(Account record);
//上面是一個完全的案例
User user =new User();
user.setId(101);
user.setUsername("joe");
user.setPassword("joe");
user.setEmail("[email protected]");
userDAO.updateByPrimaryKey(user);
相當於：
update user set username='joe',password='joe',email='[email protected]' where id=101
int updateByPrimaryKey(Account record);
//上面是一個完全的案例
User user =new User();
user.setId(101);
user.setUsername("joe");
user.setPassword("joe");
user.setEmail("[email protected]");
userDAO.updateByPrimaryKey(user);
相當於：
update user set username='joe',password='joe',email='[email protected]' where id=101
解析mapper的xml設置裝備擺設文件
我們來看看mybatis是怎樣讀取mapper的xml設置裝備擺設文件並解析個中的sql語句。
我們還記得是如許設置裝備擺設sqlSessionFactory的：
<bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean"> <property name="dataSource" ref="dataSource" /> <property name="configLocation" value="classpath:configuration.xml"></property> <property name="mapperLocations" value="classpath:com/xxx/mybatis/mapper/*.xml"/> <property name="typeAliasesPackage" value="com.tiantian.mybatis.model" /> </bean>
這裡設置裝備擺設了一個mapperLocations屬性，它是一個表達式，sqlSessionFactory會依據這個表達式讀取包com.xxx.mybaits.mapper上面的一切xml格局文件，那末詳細是怎樣依據這個屬性來讀取設置裝備擺設文件的呢？
謎底就在SqlSessionFactoryBean類中的buildSqlSessionFactory辦法中：
if (!isEmpty(this.mapperLocations)) {
for (Resource mapperLocation : this.mapperLocations) {
if (mapperLocation == null) {
continue;
}
try {
XMLMapperBuilder xmlMapperBuilder = new XMLMapperBuilder(mapperLocation.getInputStream(),
configuration, mapperLocation.toString(), configuration.getSqlFragments());
xmlMapperBuilder.parse();
} catch (Exception e) {
throw new NestedIOException("Failed to parse mapping resource: '" + mapperLocation + "'", e);
} finally {
ErrorContext.instance().reset();
}
if (logger.isDebugEnabled()) {
logger.debug("Parsed mapper file: '" + mapperLocation + "'");
}
}
}
mybatis應用XMLMapperBuilder類的實例來解析mapper設置裝備擺設文件。
public XMLMapperBuilder(Reader reader, Configuration configuration, String resource, Map<String, XNode> sqlFragments) {
this(new XPathParser(reader, true, configuration.getVariables(), new XMLMapperEntityResolver()),
configuration, resource, sqlFragments);
}
private XMLMapperBuilder(XPathParser parser, Configuration configuration, String resource, Map<String, XNode> sqlFragments) {
super(configuration);
this.builderAssistant = new MapperBuilderAssistant(configuration, resource);
this.parser = parser;
this.sqlFragments = sqlFragments;
this.resource = resource;
}
接著體系挪用xmlMapperBuilder的parse辦法解析mapper。
public void parse() {
//假如configuration對象還沒加載xml設置裝備擺設文件（防止反復加載，現實上是確認能否解析了mapper節點的屬性及內容，
//為解析它的子節點如cache、sql、select、resultMap、parameterMap等做預備），
//則從輸出流中解析mapper節點，然後再將resource的狀況置為已加載
if (!configuration.isResourceLoaded(resource)) {
configurationElement(parser.evalNode("/mapper"));
configuration.addLoadedResource(resource);
bindMapperForNamespace();
}
//解析在configurationElement函數中處置resultMap時其extends屬性指向的父對象還沒被處置的<resultMap>節點
parsePendingResultMaps();
//解析在configurationElement函數中處置cache-ref時其指向的對象不存在的<cache>節點(假如cache-ref先於其指向的cache節點加載就會湧現這類情形)
parsePendingChacheRefs();
//同上，假如cache沒加載的話處置statement時也會拋出異常
parsePendingStatements();
}
mybatis解析mapper的xml文件的進程曾經很顯著了，接上去我們看看它是怎樣解析mapper的：
private void configurationElement(XNode context) {
try {
//獲得mapper節點的namespace屬性
String namespace = context.getStringAttribute("namespace");
if (namespace.equals("")) {
throw new BuilderException("Mapper's namespace cannot be empty");
}
//設置以後namespace
builderAssistant.setCurrentNamespace(namespace);
//解析mapper的<cache-ref>節點
cacheRefElement(context.evalNode("cache-ref"));
//解析mapper的<cache>節點
cacheElement(context.evalNode("cache"));
//解析mapper的<parameterMap>節點
parameterMapElement(context.evalNodes("/mapper/parameterMap"));
//解析mapper的<resultMap>節點
resultMapElements(context.evalNodes("/mapper/resultMap"));
//解析mapper的<sql>節點
sqlElement(context.evalNodes("/mapper/sql"));
//應用XMLStatementBuilder的對象解析mapper的<select>、<insert>、<update>、<delete>節點,
//mybaits會應用MappedStatement.Builder類build一個MappedStatement對象,
//所以mybaits中一個sql對應一個MappedStatement
buildStatementFromContext(context.evalNodes("select|insert|update|delete"));
} catch (Exception e) {
throw new BuilderException("Error parsing Mapper XML. Cause: " + e, e);
}
}
configurationElement函數簡直解析了mapper節點下一切子節點，至此mybaits解析了mapper中的一切節點，並將其參加到了Configuration對象中供給給sqlSessionFactory對象隨時應用。這裡我們須要彌補講一下mybaits是怎樣應用XMLStatementBuilder類的對象的parseStatementNode函數借用MapperBuilderAssistant類對象builderAssistant的addMappedStatement解析MappedStatement並將其聯系關系到Configuration類對象的：
public void parseStatementNode() {
//ID屬性
String id = context.getStringAttribute("id");
//databaseId屬性
String databaseId = context.getStringAttribute("databaseId");
if (!databaseIdMatchesCurrent(id, databaseId, this.requiredDatabaseId)) {
return;
}
//fetchSize屬性
Integer fetchSize = context.getIntAttribute("fetchSize");
//timeout屬性
Integer timeout = context.getIntAttribute("timeout");
//parameterMap屬性
String parameterMap = context.getStringAttribute("parameterMap");
//parameterType屬性
String parameterType = context.getStringAttribute("parameterType");
Class<?> parameterTypeClass = resolveClass(parameterType);
//resultMap屬性
String resultMap = context.getStringAttribute("resultMap");
//resultType屬性
String resultType = context.getStringAttribute("resultType");
//lang屬性
String lang = context.getStringAttribute("lang");
LanguageDriver langDriver = getLanguageDriver(lang);
Class<?> resultTypeClass = resolveClass(resultType);
//resultSetType屬性
String resultSetType = context.getStringAttribute("resultSetType");
StatementType statementType = StatementType.valueOf(context.getStringAttribute("statementType", StatementType.PREPARED.toString()));
ResultSetType resultSetTypeEnum = resolveResultSetType(resultSetType);
String nodeName = context.getNode().getNodeName();
SqlCommandType sqlCommandType = SqlCommandType.valueOf(nodeName.toUpperCase(Locale.ENGLISH));
//能否是<select>節點
boolean isSelect = sqlCommandType == SqlCommandType.SELECT;
//flushCache屬性
boolean flushCache = context.getBooleanAttribute("flushCache", !isSelect);
//useCache屬性
boolean useCache = context.getBooleanAttribute("useCache", isSelect);
//resultOrdered屬性
boolean resultOrdered = context.getBooleanAttribute("resultOrdered", false);
// Include Fragments before parsing
XMLIncludeTransformer includeParser = new XMLIncludeTransformer(configuration, builderAssistant);
includeParser.applyIncludes(context.getNode());
// Parse selectKey after includes and remove them.
processSelectKeyNodes(id, parameterTypeClass, langDriver);
// Parse the SQL (pre: <selectKey> and <include> were parsed and removed)
SqlSource sqlSource = langDriver.createSqlSource(configuration, context, parameterTypeClass);
//resultSets屬性
String resultSets = context.getStringAttribute("resultSets");
//keyProperty屬性
String keyProperty = context.getStringAttribute("keyProperty");
//keyColumn屬性
String keyColumn = context.getStringAttribute("keyColumn");
KeyGenerator keyGenerator;
String keyStatementId = id + SelectKeyGenerator.SELECT_KEY_SUFFIX;
keyStatementId = builderAssistant.applyCurrentNamespace(keyStatementId, true);
if (configuration.hasKeyGenerator(keyStatementId)) {
keyGenerator = configuration.getKeyGenerator(keyStatementId);
} else {
//useGeneratedKeys屬性
keyGenerator = context.getBooleanAttribute("useGeneratedKeys",
configuration.isUseGeneratedKeys() && SqlCommandType.INSERT.equals(sqlCommandType))
? new Jdbc3KeyGenerator() : new NoKeyGenerator();
}
builderAssistant.addMappedStatement(id, sqlSource, statementType, sqlCommandType,
fetchSize, timeout, parameterMap, parameterTypeClass, resultMap, resultTypeClass,
resultSetTypeEnum, flushCache, useCache, resultOrdered,
keyGenerator, keyProperty, keyColumn, databaseId, langDriver, resultSets);
}
由以上代碼可以看出mybaits應用XPath解析mapper的設置裝備擺設文件後將個中的resultMap、parameterMap、cache、statement等節點應用聯系關系的builder創立並將獲得的對象聯系關系到configuration對象中，而這個configuration對象可以從sqlSession中獲得的，這就說明了我們在應用sqlSession對數據庫停止操作時mybaits怎樣獲得到mapper並履行個中的sql語句的成績。
