解析MyBatis原始碼實現自定義持久層框架

2022-05-28 18:02:06

自定義框架設計

使用端 ：

提供核⼼設定⽂件：

sqlMapConfig.xml : 存放資料來源資訊，引⼊mapper.xml

Mapper.xml : sql語句的設定⽂件資訊

框架端：

1.讀取設定⽂件

讀取完成以後以流的形式存在，我們不能將讀取到的設定資訊以流的形式存放在記憶體中，不好操作，可以建立JavaBean來儲存

（1）Configuration : 存放資料庫基本資訊、Map<唯⼀標識，Mapper>，唯⼀標識：namespace + "." + id

（2）MappedStatement：sql語句的id、sql語句、輸⼊引數java型別、輸出引數java型別

2.解析設定⽂件

建立SqlSessionFactoryBuilder類：

⽅法：返回值SqlSessionFactory，方法為build()：

第⼀：使⽤dom4j解析設定⽂件，將解析出來的內容封裝到Configuration和MappedStatement中

第⼆：建立SqlSessionFactory的實現類DefaultSqlSessionFactory

3.建立SqlSessionFactory：

⽅法：openSession() : 獲取SqlSession接⼝的實現類範例物件

4.建立SqlSession接⼝及實現類：主要封裝crud⽅法

⽅法：selectList(String mappedStatementId,Object... param)：查詢所有

selectOne(String mappedStatementId,Object... param)：查詢單個

具體實現：封裝JDBC完成對資料庫表的查詢操作

涉及到的設計模式 ：

Builder構建者模式、⼯⼚模式、代理模式

自定義框架實現

這裡只做比較繁瑣的查詢單條和查詢多條的實現，新增、修改、刪除的參考自行實現。

使用端

建立sqlMapConfig.xml

<configuration>
        <!--資料庫設定資訊-->
    <dataSource>
        <property name="driverClass" value="com.mysql.jdbc.Driver"></property>
        <property name="jdbcUrl" value="jdbc:mysql:///learning_db"></property>
        <property name="username" value="root"></property>
        <property name="password" value="123456"></property>
    </dataSource>
    <!--存放mapper.xml的全路徑-->
    <mapper resource="UserMapper.xml"></mapper>
</configuration>

mapper.xml

<mapper namespace="com.snf.mapper.UserMapper">
    <!--sql的唯一標識：namespace.id來組成 ： mappedStatementId-->
    <select id="findAll" resultType="com.snf.domain.User" >
        select * from user
    </select>
    <!--
        User user = new User()
        user.setId(1);
        user.setUsername("zhangsan")
    -->
    <select id="findByCondition" resultType="com.snf.domain.User" parameterType="com.snf.domain.User">
        select * from user where id = #{id} and username = #{username}
    </select>
</mapper>

User實體類

public class User {
    private Integer id;
    private String username;
    public User() {
    }
    public User(Integer id, String username) {
        this.id = id;
        this.username = username;
    }
    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;
    }
    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", username='" + username + ''' +
                '}';
    }
}

框架端

建立⼀個Maven⼦⼯程並且導⼊需要⽤到的依賴座標

<properties>
 <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
 <maven.compiler.encoding>UTF-8</maven.compiler.encoding>
 <java.version>1.8</java.version>
 <maven.compiler.source>1.8</maven.compiler.source>
 <maven.compiler.target>1.8</maven.compiler.target>
</properties>
<dependencies>
 <dependency>
 <groupId>mysql</groupId>
 <artifactId>mysql-connector-java</artifactId>
 <version>5.1.17</version>
 </dependency>
 
 <dependency>
 <groupId>c3p0</groupId>
 <artifactId>c3p0</artifactId>
 <version>0.9.1.2</version>
 </dependency>
 
 <dependency>
 <groupId>log4j</groupId>
 <artifactId>log4j</artifactId>
 <version>1.2.12</version>
 </dependency>
 
 <dependency>
 <groupId>junit</groupId>
 <artifactId>junit</artifactId>
 <version>4.10</version>
 </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>

Configuration設定類

public class Configuration {
    private DataSource dataSource;
    /**
     * key:statementId value:封裝好的mappedStatement物件
     */
    private Map<String,MappedStatement> mappedStatementMap = new HashMap<>();
    public DataSource getDataSource() {
        return dataSource;
    }
    public void setDataSource(DataSource dataSource) {
        this.dataSource = dataSource;
    }
    public Map<String, MappedStatement> getMappedStatementMap() {
        return mappedStatementMap;
    }
    public void setMappedStatementMap(Map<String, MappedStatement> mappedStatementMap) {
        this.mappedStatementMap = mappedStatementMap;
    }
}

MappedStatement類

public class MappedStatement {
    //sql語句id
    private String id;
    //sql語句
    private String sql;
    //輸入引數型別
    private String parameterType;
    //返回引數型別
    private String resultType;
    public String getId() {
        return id;
    }
    public void setId(String id) {
        this.id = id;
    }
    public String getSql() {
        return sql;
    }
    public void setSql(String sql) {
        this.sql = sql;
    }
    public String getParameterType() {
        return parameterType;
    }
    public void setParameterType(String parameterType) {
        this.parameterType = parameterType;
    }
    public String getResultType() {
        return resultType;
    }
    public void setResultType(String resultType) {
        this.resultType = resultType;
    }
}

Resources類

public class Resources {
    //以流的形式讀取組態檔
    public static InputStream getResourceAsStream(String path){
        InputStream resourceAsStream = Resources.class.getClassLoader().getResourceAsStream(path);
        return resourceAsStream;
    }
}

SqlSessionFactoryBuilder類

public class SqlSessionFactoryBuilder {
    public SqlSessionFactory build(InputStream inputStream) throws PropertyVetoException, DocumentException {
        //使用dom4j解析組態檔,將解析出來的內容封裝到Configuration中
        XMLConfigBuilder xmlConfigBuilder = new XMLConfigBuilder();
        Configuration configuration = xmlConfigBuilder.parseConfig(inputStream);

        //建立sqlSessionFactory工廠物件：生產sqlSession
        DefaultSqlSessionFactory defaultSqlSessionFactory = new DefaultSqlSessionFactory(configuration);
        return defaultSqlSessionFactory;
    }
}

XMLConfigBuilder類

public class XMLConfigBuilder {
    private Configuration configuration;

    public XMLConfigBuilder() {
        this.configuration = new Configuration();
    }

    /**
     * 使用dom4j對組態檔進行封裝,封裝Configuration
     */
    public Configuration parseConfig(InputStream inputStream) throws DocumentException, PropertyVetoException {
        Document document = new SAXReader().read(inputStream);
        Element rootElement = document.getRootElement();
        List<Element> list = rootElement.selectNodes("//property");
        Properties properties = new Properties();
        list.forEach(element -> {
            String name = element.attributeValue("name");
            String value = element.attributeValue("value");
            properties.setProperty(name, value);
        });

        ComboPooledDataSource comboPooledDataSource = new ComboPooledDataSource();
        comboPooledDataSource.setDriverClass(properties.getProperty("driverClass"));
        comboPooledDataSource.setJdbcUrl(properties.getProperty("jdbcUrl"));
        comboPooledDataSource.setUser(properties.getProperty("username"));
        comboPooledDataSource.setPassword(properties.getProperty("password"));

        configuration.setDataSource(comboPooledDataSource);

        //解析<Mapper>標籤
        List<Element> mapperList = rootElement.selectNodes("//mapper");
        mapperList.stream()
                .map(x -> x.attributeValue("resource"))
                .map(Resources::getResourceAsStream)
                .forEach(resourceAsStream -> {
                    XmlMapperBuilder xmlMapperBuilder = new XmlMapperBuilder(configuration);
                    try {
                        xmlMapperBuilder.parse(resourceAsStream);
                    } catch (DocumentException e) {
                        e.printStackTrace();
                    }
                });
        return configuration;
    }
}

XMLMapperBuilder類

public class XmlMapperBuilder {
    private Configuration configuration;

    public XmlMapperBuilder(Configuration configuration) {
        this.configuration = configuration;
    }

    public void parse(InputStream inputStream) throws DocumentException {
        Document document = new SAXReader().read(inputStream);
        Element rootElement = document.getRootElement();

        String namespace = rootElement.attributeValue("namespace");

        List<Element> list = rootElement.selectNodes("//select");
        list.forEach(element -> {
            String id = element.attributeValue("id");
            String parameterType = element.attributeValue("parameterType");
            String resultType = element.attributeValue("resultType");
            String sqlText = element.getTextTrim();
            MappedStatement mappedStatement = new MappedStatement();
            mappedStatement.setId(id);
            mappedStatement.setParameterType(parameterType);
            mappedStatement.setResultType(resultType);
            mappedStatement.setSql(sqlText);
            String key = namespace.concat(".").concat(id);
            configuration.getMappedStatementMap().put(key, mappedStatement);
        });
    }
}

SqlSessionFactory介面及DefaultSqlSessionFactory實現類

public interface SqlSessionFactory {

    SqlSession openSession();
}

public class DefaultSqlSessionFactory implements SqlSessionFactory {

    private Configuration configuration;

    public DefaultSqlSessionFactory(Configuration configuration) {
        this.configuration = configuration;
    }
    @Override
    public SqlSession openSession() {
        return new DefaultSqlSession(configuration);
    }
}

SqlSession介面及DefaultSqlSession實現類

public interface SqlSession {
    //查詢所有
    <E> List<E> selectList(String mappedStatementId,Object... params) throws IllegalAccessException, IntrospectionException, InstantiationException, NoSuchFieldException, SQLException, InvocationTargetException, ClassNotFoundException;
    //根據條件
    <T> T selectOne(String mappedStatementId,Object... params) throws IllegalAccessException, ClassNotFoundException, IntrospectionException, InstantiationException, SQLException, InvocationTargetException, NoSuchFieldException;

    //為Dao介面生成代理實現類
    <T> T getMapper(Class<T> mapperClass);
}

public class DefaultSqlSession implements SqlSession {
    private Configuration configuration;
    public DefaultSqlSession(Configuration configuration) {
        this.configuration = configuration;
    }
    @Override
    public <E> List<E> selectList(String mappedStatementId, Object... params) throws IllegalAccessException, IntrospectionException, InstantiationException, NoSuchFieldException, SQLException, InvocationTargetException, ClassNotFoundException {
        SimpleExecutor simpleExecutor = new SimpleExecutor();
        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(mappedStatementId);
        List<Object> objectList = simpleExecutor.query(configuration, mappedStatement, params);
        return (List<E>) objectList;
    }
    @Override
    public <T> T selectOne(String mappedStatementId, Object... params) throws IllegalAccessException, ClassNotFoundException, IntrospectionException, InstantiationException, SQLException, InvocationTargetException, NoSuchFieldException {
        List<Object> objectList = selectList(mappedStatementId, params);
        if (objectList.size() == 1) {
            return (T) objectList.get(0);
        } else {
            throw new RuntimeException("查詢結果為空或者返回結果過多！");
        }
    }
    @Override
    public <T> T getMapper(Class<T> mapperClass) {
        //使用JDK動態代理來為Dao介面生成代理物件,並返回
        return (T) Proxy.newProxyInstance(DefaultSqlSession.class.getClassLoader(), new Class[]{mapperClass}, ((proxy, method, args) -> {
            String methodName = method.getName();
            String className = method.getDeclaringClass().getName();
            String mappedStatementId = className.concat(".").concat(methodName);
            //獲取被呼叫方法的返回值型別
            Type genericReturnType = method.getGenericReturnType();
            //判斷是否進行了泛型型別引數化
            if (genericReturnType instanceof ParameterizedType){
                List<Object> objectList = selectList(mappedStatementId, args);
                return objectList;
            }
            return selectOne(mappedStatementId,args);
        }));
    }
}

Executor介面及SimpleExecutor實現類

public interface Executor {

    <E>List<E> query(Configuration configuration, MappedStatement mappedStatement,Object... params) throws SQLException, IntrospectionException, InvocationTargetException, IllegalAccessException, InstantiationException, ClassNotFoundException, NoSuchFieldException;
}

public class SimpleExecutor implements Executor {
    @Override
    public <E> List<E> query(Configuration configuration, MappedStatement mappedStatement, Object... params) throws SQLException, IntrospectionException, InvocationTargetException, IllegalAccessException, InstantiationException, ClassNotFoundException, NoSuchFieldException {
        //註冊驅動,獲取連線
        Connection connection = configuration.getDataSource().getConnection();

        //獲取sql語句：select * from user where id = #{id} and username = #{username}
        //轉換sql語句：select * from user where id = ? and username = ?
        //轉換的過程中,還需要對#{}裡面的引數名稱進行解析儲存
        String sql = mappedStatement.getSql();
        BoundSql boundSql = getBoundSql(sql);

        //獲取預處理物件：preparedStatement
        PreparedStatement preparedStatement = connection.prepareStatement(boundSql.getSqlText());

        //設定引數
        //獲取到了引數的全路徑
        String parameterType = mappedStatement.getParameterType();
        Class<?> parameterTypeClass = getClassType(parameterType);

        List<ParameterMapping> parameterMappingList = boundSql.getParameterMappingList();
        for (int i = 0; i < parameterMappingList.size(); i++) {
            ParameterMapping parameterMapping = parameterMappingList.get(i);
            String content = parameterMapping.getContent();

            //反射
            Field declaredField = parameterTypeClass.getDeclaredField(content);
            //暴力存取
            declaredField.setAccessible(true);
            Object o = declaredField.get(params[0]);

            preparedStatement.setObject(i + 1, o);
        }

        //執行sql
        ResultSet resultSet = preparedStatement.executeQuery();
        String resultType = mappedStatement.getResultType();
        Class<?> resultTypeClass = getClassType(resultType);

        List<Object> objectList = new ArrayList<>();
        //封裝返回結果集
        while (resultSet.next()) {
            Object o = resultTypeClass.newInstance();
            //後設資料
            ResultSetMetaData metaData = resultSet.getMetaData();
            for (int i = 1; i <= metaData.getColumnCount(); i++) {

                // 欄位名
                String columnName = metaData.getColumnName(i);
                // 欄位的值
                Object value = resultSet.getObject(columnName);

                //使用反射或者內省,根據資料庫表和實體的對應關係,完成封裝
                PropertyDescriptor propertyDescriptor = new PropertyDescriptor(columnName, resultTypeClass);
                Method writeMethod = propertyDescriptor.getWriteMethod();
                writeMethod.invoke(o, value);
            }
            objectList.add(o);

        }
        return (List<E>) objectList;
    }

    private Class<?> getClassType(String paramterType) throws ClassNotFoundException {
        if (paramterType != null) {
            Class<?> aClass = Class.forName(paramterType);
            return aClass;
        }
        return null;
    }

    /**
     * 完成對#{}的解析工作
     * 1.將#{}使用?進行代替
     * 2.解析出#{}裡面的欄位名進行儲存
     *
     * @param sql
     * @return
     */
    private BoundSql getBoundSql(String sql) {
        //標記處理類：設定標記解析器來完成對預留位置的解析處理工作
        ParameterMappingTokenHandler parameterMappingTokenHandler = new ParameterMappingTokenHandler();
        GenericTokenParser genericTokenParser = new GenericTokenParser("#{", "}", parameterMappingTokenHandler);
        //解析出來的sql
        String parseSql = genericTokenParser.parse(sql);
        //#{}裡面解析出來的引數名稱
        List<ParameterMapping> parameterMappings = parameterMappingTokenHandler.getParameterMappings();

        BoundSql boundSql = new BoundSql(parseSql, parameterMappings);
        return boundSql;
    }
}

BoundSql類

public class BoundSql {
    private String sqlText; //解析過後的sql

    private List<ParameterMapping> parameterMappingList = new ArrayList<>();

    public BoundSql(String sqlText, List<ParameterMapping> parameterMappingList) {
        this.sqlText = sqlText;
        this.parameterMappingList = parameterMappingList;
    }
    public String getSqlText() {
        return sqlText;
    }

    public void setSqlText(String sqlText) {
        this.sqlText = sqlText;
    }

    public List<ParameterMapping> getParameterMappingList() {
        return parameterMappingList;
    }

    public void setParameterMappingList(List<ParameterMapping> parameterMappingList) {
        this.parameterMappingList = parameterMappingList;
    }
}

GenericTokenParser、ParameterMapping、TokenHandler、ParameterMappingTokenHandler工具類

GenericTokenParser：解析${}或#{}中的引數名稱
ParameterMapping：儲存${}或#{}中的引數名稱
TokenHandler：替換${}或#{}處理介面
ParameterMappingTokenHandler：替換${}或#{}處理介面的實現類

public class GenericTokenParser {
  private final String openToken; //開始標記
  private final String closeToken; //結束標記
  private final TokenHandler handler; //標記處理器
  public GenericTokenParser(String openToken, String closeToken, TokenHandler handler) {
    this.openToken = openToken;
    this.closeToken = closeToken;
    this.handler = handler;
  }

  /**
   * 解析${}和#{}
   * @param text
   * @return
   * 該方法主要實現了組態檔、指令碼等片段中預留位置的解析、處理工作，並返回最終需要的資料。
   * 其中，解析工作由該方法完成，處理工作是由處理器handler的handleToken()方法來實現
   */
  public String parse(String text) {
    // 驗證引數問題，如果是null，就返回空字串。
    if (text == null || text.isEmpty()) {
      return "";
    }

    // 下面繼續驗證是否包含開始標籤，如果不包含，預設不是預留位置，直接原樣返回即可，否則繼續執行。
    int start = text.indexOf(openToken, 0);
    if (start == -1) {
      return text;
    }

   // 把text轉成字元陣列src，並且定義預設偏移量offset=0、儲存最終需要返回字串的變數builder，
    // text變數中預留位置對應的變數名expression。判斷start是否大於-1(即text中是否存在openToken)，如果存在就執行下面程式碼
    char[] src = text.toCharArray();
    int offset = 0;
    final StringBuilder builder = new StringBuilder();
    StringBuilder expression = null;
    while (start > -1) {
     // 判斷如果開始標記前如果有跳脫字元，就不作為openToken進行處理，否則繼續處理
      if (start > 0 && src[start - 1] == '\') {
        builder.append(src, offset, start - offset - 1).append(openToken);
        offset = start + openToken.length();
      } else {
        //重置expression變數，避免空指標或者老資料干擾。
        if (expression == null) {
          expression = new StringBuilder();
        } else {
          expression.setLength(0);
        }
        builder.append(src, offset, start - offset);
        offset = start + openToken.length();
        int end = text.indexOf(closeToken, offset);
        while (end > -1) {////存在結束標記時
          if (end > offset && src[end - 1] == '\') {//如果結束標記前面有跳脫字元時
            // this close token is escaped. remove the backslash and continue.
            expression.append(src, offset, end - offset - 1).append(closeToken);
            offset = end + closeToken.length();
            end = text.indexOf(closeToken, offset);
          } else {//不存在跳脫字元，即需要作為引數進行處理
            expression.append(src, offset, end - offset);
            offset = end + closeToken.length();
            break;
          }
        }
        if (end == -1) {
          // close token was not found.
          builder.append(src, start, src.length - start);
          offset = src.length;
        } else {
          //首先根據引數的key（即expression）進行引數處理，返回?作為預留位置
          builder.append(handler.handleToken(expression.toString()));
          offset = end + closeToken.length();
        }
      }
      start = text.indexOf(openToken, offset);
    }
    if (offset < src.length) {
      builder.append(src, offset, src.length - offset);
    }
    return builder.toString();
  }
}

public class ParameterMapping {

    private String content;

    public ParameterMapping(String content) {
        this.content = content;
    }

    public String getContent() {
        return content;
    }

    public void setContent(String content) {
        this.content = content;
    }
}

public interface TokenHandler {
  String handleToken(String content);
}

public class ParameterMappingTokenHandler implements TokenHandler {
	private List<ParameterMapping> parameterMappings = new ArrayList<>();

	// context是引數名稱 #{id} #{username}

	public String handleToken(String content) {
		parameterMappings.add(buildParameterMapping(content));
		return "?";
	}

	private ParameterMapping buildParameterMapping(String content) {
		ParameterMapping parameterMapping = new ParameterMapping(content);
		return parameterMapping;
	}

	public List<ParameterMapping> getParameterMappings() {
		return parameterMappings;
	}

	public void setParameterMappings(List<ParameterMapping> parameterMappings) {
		this.parameterMappings = parameterMappings;
	}
}

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解析MyBatis原始碼實現自定義持久層框架

目錄

自定義框架設計

自定義框架實現

使用端

框架端

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