一、自定義Mybatis分析
1、執行查詢分析
Mybatis在使用代理dao的方式實現增刪改查時做了什麼事:
只做了兩件事:
1、創建代理對象;
2、在代理對象中調用selectList;
解析
1圖解:
2步驟分析:
第一步:根據配置文件創建Connection對象,註冊啓動,獲取連接;
第二步:獲取預處理對象PreparedStatement,此時需要sql語句,conn.preparedStatement(sql);
第三步:執行查詢
ResultSet resultSet = preparedStatement.executeQuery();
第四步:遍歷結果集用於封裝(使用反射封裝)
List<E> list = new ArrayList();
while(resultSet.next()){
E element = (E)Class.forName(配置的全限定類名).newInstance();
//進行封裝,把每個rs內容都添加到element中
//
我們的實體類屬性是和表中的列名是一致的,所以我們可以把表中的列名看作是屬性名,
就可以通過反射的方式來根據名稱獲取每個屬性,並把值賦進去;
//
//把element添加到list中
list.add(element);
}
第五步:返回list return list;
3備註:
要想讓操作數據庫的Java方法執行,必須提供以下兩條數據信息:
1、連接數據;
2、映射數據(Mapper):
-- 執行SQL的語句;
-- 封裝結果的實體類的全限定類名;
(把這兩個信息組合起來定義成一個對象)
2、創建代理對象分析
3、自定義mybatis能通過入門案例看到的類
class Resources
class SqlSessionFactoryBuilder
interface SqlSessionFactory
interface SqlSession
pom.xml
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>org.example</groupId>
<artifactId>mybatis20200127</artifactId>
<version>1.0-SNAPSHOT</version>
<packaging>jar</packaging>
<dependencies>
<!-- <dependency>-->
<!-- <groupId>org.mybatis</groupId>-->
<!-- <artifactId>mybatis</artifactId>-->
<!-- <version>3.5.3</version>-->
<!-- </dependency>-->
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>8.0.19</version>
</dependency>
<dependency>
<groupId>log4j</groupId>
<artifactId>log4j</artifactId>
<version>1.2.17</version>
</dependency>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.13-beta-3</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>dom4j</groupId>
<artifactId>dom4j</artifactId>
<version>1.6.1</version>
</dependency>
<dependency>
<groupId>jaxen</groupId>
<artifactId>jaxen</artifactId>
<version>1.1.6</version>
</dependency>
</dependencies>
</project>
測試代碼:
Main.java
package com.zibo.mybatis;
import com.zibo.mybatis.dao.IUserDao;
import com.zibo.mybatis.domain.User;
import com.zibo.mybatis.io.Resources;
import com.zibo.mybatis.session.SqlSession;
import com.zibo.mybatis.session.SqlSessionFactory;
import com.zibo.mybatis.session.SqlSessionFactoryBuilder;
import java.io.IOException;
import java.io.InputStream;
import java.util.List;
public class Main {
public static void main(String[] args) throws IOException {
//1、讀取配置文件
InputStream in = Resources.getResourceAsStream("SqlMapConfig.xml");
//2、創建SqlSessionFactory工廠
SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
SqlSessionFactory factory = builder.build(in);
//3、使用工廠生產SqlSession對象
SqlSession sqlSession = factory.openSession();
//4、使用SqlSession創建Dao接口的代理對象
IUserDao iUserDao = sqlSession.getMapper(IUserDao.class);
//5、使用代理對象執行方法
System.out.println("==============================");
List<User> users = iUserDao.findAll();
for (User user : users) {
System.out.println(user);
}
//6、釋放資源
sqlSession.close();
in.close();
}
}
代碼文件:
註解Select:
package com.zibo.mybatis.annotations;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
/**
* @author 黑馬程序員
* @Company http://www.ithiema.com
* 查詢的註解
*/
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface Select {
/**
* 配置SQL語句的
* @return
*/
String value();
}
Configuration:
package com.zibo.mybatis.cfg;
import java.util.HashMap;
import java.util.Map;
//自定義mybatis的配置類
public class Configuration {
private String driver;
private String url;
private String username;
private String password;
private Map<String,Mapper> mappers = new HashMap<String, Mapper>();
public Map<String, Mapper> getMappers() {
return mappers;
}
public void setMappers(Map<String, Mapper> mappers) {
this.mappers.putAll(mappers);//此處使用追加的方式
}
public String getDriver() {
return driver;
}
public void setDriver(String driver) {
this.driver = driver;
}
public String getUrl() {
return url;
}
public void setUrl(String url) {
this.url = url;
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
}
Mapper:
package com.zibo.mybatis.cfg;
//用於封裝執行的SQL語句和結果類的全限定類名
public class Mapper {
private String queryString;//SQL
private String resultType;//實體類的全限定類名
public String getQueryString() {
return queryString;
}
public void setQueryString(String queryString) {
this.queryString = queryString;
}
public String getResultType() {
return resultType;
}
public void setResultType(String resultType) {
this.resultType = resultType;
}
}
IUserDao接口:
package com.zibo.mybatis.dao;
import com.zibo.mybatis.annotations.Select;
import com.zibo.mybatis.domain.User;
import java.util.List;
public interface IUserDao {
// 查詢所有
@Select("select * from user")
List<User> findAll();
}
實體類User:
package com.zibo.mybatis.domain;
import java.io.Serializable;
import java.util.Date;
public class User implements Serializable {
private Integer id;
private String username;
private Date birthday;
private String sex;
private String address;
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public Date getBirthday() {
return birthday;
}
public void setBirthday(Date birthday) {
this.birthday = birthday;
}
public String getSex() {
return sex;
}
public void setSex(String sex) {
this.sex = sex;
}
public String getAddress() {
return address;
}
public void setAddress(String address) {
this.address = address;
}
@Override
public String toString() {
return "User{" +
"id=" + id +
", username='" + username + '\'' +
", birthday=" + birthday +
", sex='" + sex + '\'' +
", address='" + address + '\'' +
'}';
}
}
Resources:
package com.zibo.mybatis.io;
import java.io.InputStream;
//使用類加載器讀取配置文件的類
public class Resources {
//根據傳入的參數獲取一個字節輸入流
public static InputStream getResourceAsStream(String filePath){
return Resources.class.getClassLoader().getResourceAsStream(filePath);
}
}
MapperProxy:
package com.zibo.mybatis.proxy;
import com.zibo.mybatis.cfg.Mapper;
import com.zibo.mybatis.utils.Executor;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.sql.Connection;
import java.util.Map;
public class MapperProxy implements InvocationHandler {
//map的key是全限定類名+方法名
private Map<String,Mapper> mappers;
private Connection coon;
public MapperProxy(Map<String, Mapper> mappers, Connection coon) {
this.mappers = mappers;
this.coon = coon;
}
//用於對方法進行增強,調用selectList方法
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
//1、獲取方法名
String methodName = method.getName();
//2、獲取方法所在類的名稱
String className = method.getDeclaringClass().getName();
//3、組合key
String key = className + "." + methodName;
//4、獲取mappers中的mapper對象
Mapper mapper = mappers.get(key);
//5、判斷是否有mapper
if(mapper == null){
throw new IllegalArgumentException("傳入的參數有誤");
}
//6、調用工具類,查詢所有
return new Executor().selectList(mapper,coon);
}
}
DefaultSqlSession:
package com.zibo.mybatis.session.defaults;
import com.zibo.mybatis.cfg.Configuration;
import com.zibo.mybatis.proxy.MapperProxy;
import com.zibo.mybatis.session.SqlSession;
import com.zibo.mybatis.utils.DataSourceUtil;
import java.lang.reflect.Proxy;
import java.sql.Connection;
import java.sql.SQLException;
//SqlSession接口的實現類
public class DefaultSqlSession implements SqlSession {
private Configuration cfg;
private Connection connection;
public DefaultSqlSession(Configuration cfg) {
this.cfg = cfg;
this.connection = DataSourceUtil.getConnection(cfg);
}
//用於創建代理對象
public <T> T getMapper(Class<T> daoInterfaceClass) {
return (T)Proxy.newProxyInstance(daoInterfaceClass.getClassLoader(),new Class[]{daoInterfaceClass},new MapperProxy(cfg.getMappers(),connection));
}
//用於釋放資源
public void close() {
if(connection!=null) {
try {
connection.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
}
DefaultSqlSessionFactory:
package com.zibo.mybatis.session.defaults;
import com.zibo.mybatis.cfg.Configuration;
import com.zibo.mybatis.session.SqlSession;
import com.zibo.mybatis.session.SqlSessionFactory;
//SqlSessionFactory接口的實現類
public class DefaultSqlSessionFactory implements SqlSessionFactory {
private Configuration cfg;
public DefaultSqlSessionFactory(Configuration cfg) {
this.cfg = cfg;
}
//用於創建一個新的數據庫對象
public SqlSession openSession() {
return new DefaultSqlSession(cfg);
}
}
SqlSession:
package com.zibo.mybatis.session;
//自定義mybatis中與數據庫交互的核心類,裏面可以創建dao接口的代理對象
public interface SqlSession {
//根據參數創建一個代理對象,參數是dao的接口字節碼
<T> T getMapper(Class<T> daoInterfaceClass);
//釋放資源
void close();
}
SqlSessionFactory:
package com.zibo.mybatis.session;
public interface SqlSessionFactory {
//用於打開一個新的SqlSession對象
SqlSession openSession();
}
SqlSessionFactoryBuilder:
package com.zibo.mybatis.session;
import com.zibo.mybatis.cfg.Configuration;
import com.zibo.mybatis.session.defaults.DefaultSqlSessionFactory;
import com.zibo.mybatis.utils.XMLConfigBuilder;
import java.io.InputStream;
//用於創建一個SqlSessionFactory工廠對象
public class SqlSessionFactoryBuilder {
//根據配置文件構建SqlSessionFactory工廠
public SqlSessionFactory build(InputStream config){
Configuration cfg = XMLConfigBuilder.loadConfiguration(config);
return new DefaultSqlSessionFactory(cfg);
}
}
DataSourceUtil:
package com.zibo.mybatis.utils;
import com.zibo.mybatis.cfg.Configuration;
import java.sql.Connection;
import java.sql.DriverManager;
//用於創建數據源的工具類
public class DataSourceUtil {
//用於獲取一個連接
public static Connection getConnection(Configuration cfg){
try {
Class.forName(cfg.getDriver());
return DriverManager.getConnection(cfg.getUrl(),cfg.getUsername(),cfg.getPassword());
} catch (Exception e) {
throw new RuntimeException(e);
}
}
}
Executor:
package com.zibo.mybatis.utils;
import com.zibo.mybatis.cfg.Mapper;
import java.beans.PropertyDescriptor;
import java.lang.reflect.Method;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.util.ArrayList;
import java.util.List;
/**
* @author 黑馬程序員
* @Company http://www.ithiema.com
* 負責執行SQL語句,並且封裝結果集
*/
public class Executor {
public <E> List<E> selectList(Mapper mapper, Connection conn) {
PreparedStatement pstm = null;
ResultSet rs = null;
try {
//1.取出mapper中的數據
String queryString = mapper.getQueryString();//select * from user
String resultType = mapper.getResultType();//com.itheima.domain.User
Class domainClass = Class.forName(resultType);
//2.獲取PreparedStatement對象
pstm = conn.prepareStatement(queryString);
//3.執行SQL語句,獲取結果集
rs = pstm.executeQuery();
//4.封裝結果集
List<E> list = new ArrayList<E>();//定義返回值
while(rs.next()) {
//實例化要封裝的實體類對象
E obj = (E)domainClass.newInstance();
//取出結果集的元信息:ResultSetMetaData
ResultSetMetaData rsmd = rs.getMetaData();
//取出總列數
int columnCount = rsmd.getColumnCount();
//遍歷總列數
for (int i = 1; i <= columnCount; i++) {
//獲取每列的名稱,列名的序號是從1開始的
String columnName = rsmd.getColumnName(i);
//根據得到列名,獲取每列的值
Object columnValue = rs.getObject(columnName);
//給obj賦值:使用Java內省機制(藉助PropertyDescriptor實現屬性的封裝)
PropertyDescriptor pd = new PropertyDescriptor(columnName,domainClass);//要求:實體類的屬性和數據庫表的列名保持一種
//獲取它的寫入方法
Method writeMethod = pd.getWriteMethod();
//把獲取的列的值,給對象賦值
writeMethod.invoke(obj,columnValue);
}
//把賦好值的對象加入到集合中
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();
}
}
}
}
XMLConfigBuilder:
package com.zibo.mybatis.utils;
import com.zibo.mybatis.annotations.Select;
import com.zibo.mybatis.cfg.Configuration;
import com.zibo.mybatis.cfg.Mapper;
import com.zibo.mybatis.io.Resources;
import org.dom4j.Attribute;
import org.dom4j.Document;
import org.dom4j.Element;
import org.dom4j.io.SAXReader;
import java.io.IOException;
import java.io.InputStream;
import java.lang.reflect.Method;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
/**
* @author 黑馬程序員
* @Company http://www.ithiema.com
* 用於解析配置文件
*/
public class XMLConfigBuilder {
/**
* 解析主配置文件,把裏面的內容填充到DefaultSqlSession所需要的地方
* 使用的技術:
* dom4j+xpath
*/
public static Configuration loadConfiguration(InputStream config){
try{
//定義封裝連接信息的配置對象(mybatis的配置對象)
Configuration cfg = new Configuration();
//1.獲取SAXReader對象
SAXReader reader = new SAXReader();
//2.根據字節輸入流獲取Document對象
Document document = reader.read(config);
//3.獲取根節點
Element root = document.getRootElement();
//4.使用xpath中選擇指定節點的方式,獲取所有property節點
List<Element> propertyElements = root.selectNodes("//property");
//5.遍歷節點
for(Element propertyElement : propertyElements){
//判斷節點是連接數據庫的哪部分信息
//取出name屬性的值
String name = propertyElement.attributeValue("name");
if("driver".equals(name)){
//表示驅動
//獲取property標籤value屬性的值
String driver = propertyElement.attributeValue("value");
cfg.setDriver(driver);
}
if("url".equals(name)){
//表示連接字符串
//獲取property標籤value屬性的值
String url = propertyElement.attributeValue("value");
cfg.setUrl(url);
}
if("username".equals(name)){
//表示用戶名
//獲取property標籤value屬性的值
String username = propertyElement.attributeValue("value");
cfg.setUsername(username);
}
if("password".equals(name)){
//表示密碼
//獲取property標籤value屬性的值
String password = propertyElement.attributeValue("value");
cfg.setPassword(password);
}
}
//取出mappers中的所有mapper標籤,判斷他們使用了resource還是class屬性
List<Element> mapperElements = root.selectNodes("//mappers/mapper");
//遍歷集合
for(Element mapperElement : mapperElements){
//判斷mapperElement使用的是哪個屬性
Attribute attribute = mapperElement.attribute("resource");
if(attribute != null){
System.out.println("使用的是XML");
//表示有resource屬性,用的是XML
//取出屬性的值
String mapperPath = attribute.getValue();//獲取屬性的值"com/itheima/dao/IUserDao.xml"
//把映射配置文件的內容獲取出來,封裝成一個map
Map<String, Mapper> mappers = loadMapperConfiguration(mapperPath);
//給configuration中的mappers賦值
cfg.setMappers(mappers);
}else{
System.out.println("使用的是註解");
//表示沒有resource屬性,用的是註解
//獲取class屬性的值
String daoClassPath = mapperElement.attributeValue("class");
//根據daoClassPath獲取封裝的必要信息
Map<String,Mapper> mappers = loadMapperAnnotation(daoClassPath);
//給configuration中的mappers賦值
cfg.setMappers(mappers);
}
}
//返回Configuration
return cfg;
}catch(Exception e){
throw new RuntimeException(e);
}finally{
try {
config.close();
}catch(Exception e){
e.printStackTrace();
}
}
}
/**
* 根據傳入的參數,解析XML,並且封裝到Map中
* @param mapperPath 映射配置文件的位置
* @return map中包含了獲取的唯一標識(key是由dao的全限定類名和方法名組成)
* 以及執行所需的必要信息(value是一個Mapper對象,裏面存放的是執行的SQL語句和要封裝的實體類全限定類名)
*/
private static Map<String,Mapper> loadMapperConfiguration(String mapperPath)throws IOException {
InputStream in = null;
try{
//定義返回值對象
Map<String,Mapper> mappers = new HashMap<String,Mapper>();
//1.根據路徑獲取字節輸入流
in = Resources.getResourceAsStream(mapperPath);
//2.根據字節輸入流獲取Document對象
SAXReader reader = new SAXReader();
Document document = reader.read(in);
//3.獲取根節點
Element root = document.getRootElement();
//4.獲取根節點的namespace屬性取值
String namespace = root.attributeValue("namespace");//是組成map中key的部分
//5.獲取所有的select節點
List<Element> selectElements = root.selectNodes("//select");
//6.遍歷select節點集合
for(Element selectElement : selectElements){
//取出id屬性的值 組成map中key的部分
String id = selectElement.attributeValue("id");
//取出resultType屬性的值 組成map中value的部分
String resultType = selectElement.attributeValue("resultType");
//取出文本內容 組成map中value的部分
String queryString = selectElement.getText();
//創建Key
String key = namespace+"."+id;
//創建Value
Mapper mapper = new Mapper();
mapper.setQueryString(queryString);
mapper.setResultType(resultType);
//把key和value存入mappers中
mappers.put(key,mapper);
}
return mappers;
}catch(Exception e){
throw new RuntimeException(e);
}finally{
in.close();
}
}
/**
* 根據傳入的參數,得到dao中所有被select註解標註的方法。
* 根據方法名稱和類名,以及方法上註解value屬性的值,組成Mapper的必要信息
* @param daoClassPath
* @return
*/
private static Map<String,Mapper> loadMapperAnnotation(String daoClassPath)throws Exception{
//定義返回值對象
Map<String,Mapper> mappers = new HashMap<String, Mapper>();
//1.得到dao接口的字節碼對象
Class daoClass = Class.forName(daoClassPath);
//2.得到dao接口中的方法數組
Method[] methods = daoClass.getMethods();
//3.遍歷Method數組
for(Method method : methods){
//取出每一個方法,判斷是否有select註解
boolean isAnnotated = method.isAnnotationPresent(Select.class);
if(isAnnotated){
//創建Mapper對象
Mapper mapper = new Mapper();
//取出註解的value屬性值
Select selectAnno = method.getAnnotation(Select.class);
String queryString = selectAnno.value();
mapper.setQueryString(queryString);
//獲取當前方法的返回值,還要求必須帶有泛型信息
Type type = method.getGenericReturnType();//List<User>
//判斷type是不是參數化的類型
if(type instanceof ParameterizedType){
//強轉
ParameterizedType ptype = (ParameterizedType)type;
//得到參數化類型中的實際類型參數
Type[] types = ptype.getActualTypeArguments();
//取出第一個
Class domainClass = (Class)types[0];
//獲取domainClass的類名
String resultType = domainClass.getName();
//給Mapper賦值
mapper.setResultType(resultType);
}
//組裝key的信息
//獲取方法的名稱
String methodName = method.getName();
String className = method.getDeclaringClass().getName();
String key = className+"."+methodName;
//給map賦值
mappers.put(key,mapper);
}
}
return mappers;
}
}
資源文件:
IUserDao.xml:
<?xml version="1.0" encoding="UTF-8"?>
<mapper namespace="com.zibo.mybatis.dao.IUserDao">
<!-- 配置查詢所有-->
<select id="findAll" resultType="com.zibo.mybatis.domain.User">
select * from user;
</select>
</mapper>
log4j.properties:
# Set root category priority to INFO and its only appender to CONSOLE.
#log4j.rootCategory=INFO, CONSOLE debug info warn error fatal
log4j.rootCategory=debug, CONSOLE, LOGFILE
# Set the enterprise logger category to FATAL and its only appender to CONSOLE.
log4j.logger.org.apache.axis.enterprise=FATAL, CONSOLE
# CONSOLE is set to be a ConsoleAppender using a PatternLayout.
log4j.appender.CONSOLE=org.apache.log4j.ConsoleAppender
log4j.appender.CONSOLE.layout=org.apache.log4j.PatternLayout
log4j.appender.CONSOLE.layout.ConversionPattern=%d{ISO8601} %-6r [%15.15t] %-5p %30.30c %x - %m\n
# LOGFILE is set to be a File appender using a PatternLayout.
log4j.appender.LOGFILE=org.apache.log4j.FileAppender
log4j.appender.LOGFILE.File=d:\axis.log
log4j.appender.LOGFILE.Append=true
log4j.appender.LOGFILE.layout=org.apache.log4j.PatternLayout
log4j.appender.LOGFILE.layout.ConversionPattern=%d{ISO8601} %-6r [%15.15t] %-5p %30.30c %x - %m\n
SqlMapConfig.xml:
<?xml version="1.0" encoding="UTF-8"?>
<configuration>
<!-- 配置環境-->
<environments default="mysql">
<!-- mysql的配置-->
<environment id="mysql">
<!-- 配置事務的類型-->
<transactionManager type="JDBC">
</transactionManager>
<!-- 配置數據源(連接池)-->
<dataSource type="POOLED">
<!-- 配置數據庫的4個基本信息-->
<property name="driver" value="com.mysql.cj.jdbc.Driver"/>
<property name="url" value="jdbc:mysql://localhost:3306/zibo?serverTimezone=UTC"/>
<property name="username" value="root"/>
<property name="password" value="zibo15239417242"/>
</dataSource>
</environment>
</environments>
<!-- 指定映射配置文件的位置-->
<mappers>
<mapper class="com.zibo.mybatis.dao.IUserDao"/>
</mappers>
</configuration>
各文件位置結構圖: