自定义 Mybatis 框架的分析
- 代码展示:
InputStream in = Resources.getResourceAsStream("SqlMapConifg.xml");
SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
SqlSessionFactory sqlSessionFactory = builder.build(in);
SqlSession session = sqlSessionFactory.openSession();
IUserDao dao = session.getMapper(IUserDao.class);
List<User> users= dao.findAll();
System.out.println(users);
session.close();
in.close();
- 分析流程
自定义Mybatis框架(基于XML)
- 导入所需要的jar包和依赖
<dependencies>
<!-- 日志坐标 -->
<dependency>
<groupId>log4j</groupId>
<artifactId>log4j</artifactId>
<version>1.2.12</version>
</dependency>
<!-- 解析 xml 的 dom4j -->
<dependency>
<groupId>dom4j</groupId>
<artifactId>dom4j</artifactId>
<version>1.6.1</version>
</dependency>
<!-- mysql 驱动 -->
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>5.1.6</version>
</dependency>
<!-- dom4j 的依赖包 jaxen -->
<dependency>
<groupId>jaxen</groupId>
<artifactId>jaxen</artifactId>
<version>1.1.6</version>
</dependency>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.10</version>
</dependency>
</dependencies>
- 引入 工具类到项目中
public class XMLConfigBuilder {
public static void loadConfiguration(DefaultSqlSession session,InputStream
config){
try{
Configuration cfg = new Configuration();
SAXReader reader = new SAXReader();
Document document = reader.read(config);
Element root = document.getRootElement();
List<Element> propertyElements = root.selectNodes("//property");
for(Element propertyElement : propertyElements){
String name = propertyElement.attributeValue("name");
if("driver".equals(name)){
String driver = propertyElement.attributeValue("value");
cfg.setDriver(driver);
}
if("url".equals(name)){
String url = propertyElement.attributeValue("value");
cfg.setUrl(url);
}
if("username".equals(name)){
String username = propertyElement.attributeValue("value");
cfg.setUsername(username);
}
if("password".equals(name)){
String password = propertyElement.attributeValue("value");
cfg.setPassword(password);
}
}
List<Element> mapperElements = root.selectNodes("//mappers/mapper");
for(Element mapperElement : mapperElements){
Attribute attribute = mapperElement.attribute("resource");
if(attribute != null){
System.out.println("使用的是 XML");
String mapperPath = attribute.getValue();
"com/itheima/dao/IUserDao.xml"
Map<String,Mapper> mappers = loadMapperConfiguration(mapperPath);
cfg.setMappers(mappers);
}else{
System.out.println("使用的是注解");
String daoClassPath = mapperElement.attributeValue("class");
Map<String,Mapper> mappers = loadMapperAnnotation(daoClassPath);
cfg.setMappers(mappers);
}
}
session.setCfg(cfg);
}catch(Exception e){
throw new RuntimeException(e);
}finally{
try {
config.close();
}catch(Exception e){
e.printStackTrace();
}
}
}
根据传入的参数,解析 XML,并且封装到 Map 中
private static Map<String,Mapper> loadMapperConfiguration(String
mapperPath)throws IOException {
InputStream in = null;
try{
Map<String,Mapper> mappers = new HashMap<String,Mapper>();
in = Resources.getResourceAsStream(mapperPath);
SAXReader reader = new SAXReader();
Document document = reader.read(in);
Element root = document.getRootElement();
String namespace = root.attributeValue("namespace");
部分
List<Element> selectElements = root.selectNodes("//select");
for(Element selectElement : selectElements){
String id = selectElement.attributeValue("id");
String resultType = selectElement.attributeValue("resultType");
String queryString = selectElement.getText();
String key = namespace+"."+id;
Mapper mapper = new Mapper();
mapper.setQueryString(queryString);
mapper.setResultType(resultType);
mappers.put(key,mapper);
}
return mappers;
}catch(Exception e){
throw new RuntimeException(e);
}finally{
in.close();
}
}
根据传入的参数,得到 dao 中所有被 select 注解标注的方法。
根据方法名称和类名,以及方法上注解 value 属性的值,组成 Mapper 的必要信息
private static Map<String,Mapper> loadMapperAnnotation(StringdaoClassPath)throws Exception{
Map<String,Mapper> mappers = new HashMap<String, Mapper>();
Class daoClass = Class.forName(daoClassPath);
Method[] methods = daoClass.getMethods();
for(Method method : methods){
boolean isAnnotated = method.isAnnotationPresent(Select.class);
if(isAnnotated){
Mapper mapper = new Mapper();
Select selectAnno = method.getAnnotation(Select.class);
String queryString = selectAnno.value();
mapper.setQueryString(queryString);
Type type = method.getGenericReturnType();
if(type instanceof ParameterizedType){
ParameterizedType ptype = (ParameterizedType)type;
Type[] types = ptype.getActualTypeArguments();
Class domainClass = (Class)types[0];
String resultType = domainClass.getName();
mapper.setResultType(resultType);
}
String methodName = method.getName();
String className = method.getDeclaringClass().getName();
String key = className+"."+methodName;
mappers.put(key,mapper);
}
}
return mappers;
}
}
负责执行 SQL 语句,并且封装结果集
public class Executor {
public <E> List<E> selectList(Mapper mapper, Connection conn) {
PreparedStatement pstm = null;
ResultSet rs = null;
try {
String queryString = mapper.getQueryString();
String resultType = mapper.getResultType();
Class domainClass = Class.forName(resultType);
pstm = conn.prepareStatement(queryString);
rs = pstm.executeQuery();
List<E> list = new ArrayList<E>();
while(rs.next()) {
E obj = (E)domainClass.newInstance();
ResultSetMetaData rsmd = rs.getMetaData();
int columnCount = rsmd.getColumnCount();
for (int i = 1; i <= columnCount; i++) {
String columnName = rsmd.getColumnName(i);
Object columnValue = rs.getObject(columnName);
PropertyDescriptor pd = new
PropertyDescriptor(columnName,domainClass);
Method writeMethod = pd.getWriteMethod();
username);
writeMethod.invoke(obj,columnValue);
}
list.add(obj);
}
return list;
} catch (Exception e) {
throw new RuntimeException(e);
} finally {
release(pstm,rs);
}
}
private void release(PreparedStatement pstm,ResultSet rs){
if(rs != null){
try {
rs.close();
}catch(Exception e){
e.printStackTrace();
}
}
if(pstm != null){
try {
pstm.close();
}catch(Exception e){
e.printStackTrace();
}
}
}
}
public class DataSourceUtil {
public static Connection getConnection(Configuration cfg) {
try {
Class.forName(cfg.getDriver());
Connection conn =
DriverManager.getConnection(cfg.getUrl(),cfg.getUsername() , cfg.getPassword());
return conn;
} catch (Exception e) {
throw new RuntimeException(e);
}
}
}
- 编写构建者类
public class SqlSessionFactoryBuilder {
public SqlSessionFactory build(InputStream in) {
DefaultSqlSessionFactory factory = new DefaultSqlSessionFactory();
factory.setConfig(in);
return factory;
}
}
- 编写 SqlSessionFactory 接口和实现类
public interface SqlSessionFactory {
SqlSession openSession();
}
public class DefaultSqlSessionFactory implements SqlSessionFactory {
private InputStream config = null;
public void setConfig(InputStream config) {
this.config = config;
}
@Override
public SqlSession openSession() {
DefaultSqlSession session = new DefaultSqlSession();
XMLConfigBuilder.loadConfiguration(session, config);
return session;
}
}
- 编写 SqlSession 接口和实现类
public interface SqlSession {
<T> T getMapper(Class<T> daoClass);
void close();
}
public class DefaultSqlSession implements SqlSession {
private Configuration cfg;
public void setCfg(Configuration cfg) {
this.cfg = cfg;
}
private Connection conn;
public Connection getConn() {
try {
conn = DataSourceUtil.getDataSource(cfg).getConnection();
return conn;
} catch (Exception e) {
throw new RuntimeException(e);
}
}
@Override
public <T> T getMapper(Class<T> daoClass) {
conn = getConn();
System.out.println(conn);
T daoProxy = (T) Proxy.newProxyInstance(daoClass.getClassLoader(),new
Class[] {daoClass}, new MapperProxyFactory(cfg.getMappers(),conn));
return daoProxy;
}
@Override
public void close() {
try {
System.out.println(conn);
conn.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
public <E> List<E> selectList(String statement){
Mapper mapper = cfg.getMappers().get(statement);
return new Executor().selectList(mapper,conn);
}
}
- 编写用于创建 Dao 接口代理对象的类
public class MapperProxyFactory implements InvocationHandler {
private Map<String,Mapper> mappers;
private Connection conn;
public MapperProxyFactory(Map<String, Mapper> mappers,Connection conn) {
this.mappers = mappers;
this.conn = conn;
}
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable
{
String methodName = method.getName();
String className = method.getDeclaringClass().getName();
String key = className+"."+methodName;
Mapper mapper = mappers.get(key);
if(mapper == null) {
throw new IllegalArgumentException("传入的参数有误,无法获取执行的必要条件
");
}
Executor executor = new Executor();
return executor.selectList(mapper, conn);
}
}
- 运行测试类
public class MybatisTest {
public static void main(String[] args)throws Exception {
InputStream in = Resources.getResourceAsStream("SqlMapConfig.xml");
SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
SqlSessionFactory factory = builder.build(in);
SqlSession session = factory.openSession();
IUserDao userDao = session.getMapper(IUserDao.class);
List<User> users = userDao.findAll();
for(User user : users) {
System.out.println(user);
}
session.close();
in.close();
}
}
- 详细过程