自定義Mybatis簡單實現方法
阿新 • • 發佈：2021-06-16
首先要明白mybatis為了解決jdbc存在的什麼問題，最簡單常見的就是以下幾個
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資料庫連線建立、釋放頻繁造成系統資源浪費，影響系統性能
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SQL語句在程式碼中硬編碼，不移維護
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對結果集解析存在硬編碼
一.自定義框架設計思路
使用端:
提供配置檔案
SqlMapConfig.xml：存放資料來源資訊，引入mapper.xml
Mapper.xml：存放sql語句
自定義框架：
二、程式碼
Pom引入外掛
<dependencies> <dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> <version>8.0.25</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和MapperdStatement
public class Configuration { private DataSource dataSource; // key: statementid value:封裝好的mappedStatement物件 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; } }
public class MappedStatement { //id標識 private String id; //返回值型別 private String resultType; //引數值型別 private String parameterType; //sql語句 private String sql; //執行方法是select還是update private String type; public String getType() { return type; } public void setType(String type) { this.type = type; } public String getId() { return id; } public void setId(String id) { this.id = id; } public String getResultType() { return resultType; } public void setResultType(String resultType) { this.resultType = resultType; } public String getParameterType() { return parameterType; } public void setParameterType(String parameterType) { this.parameterType = parameterType; } public String getSql() { return sql; } public void setSql(String sql) { this.sql = sql; } }
XmlConfigBulider和XmlMapperBulider
public class XmlConfigBuilder { private Configuration configuration; public XmlConfigBuilder() { this.configuration = new Configuration(); } /** * 該方法就是使用dom4j對配置檔案進行解析，封裝到Configuration */ public Configuration parseConfig(InputStream inputStream) throws DocumentException, PropertyVetoException { Document document = new SAXReader().read(inputStream); //<configuration> Element rootElement = document.getRootElement(); List<Element> list = rootElement.selectNodes("//property"); Properties properties = new Properties(); for (Element element : list) { 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); //mapper.xml解析: 拿到路徑--位元組輸入流---dom4j進行解析 List<Element> mapperList = rootElement.selectNodes("//mapper"); for (Element element : mapperList) { String mapperPath = element.attributeValue("resource"); InputStream resourceAsSteam = Resources.getResourceAsSteam(mapperPath); XmlMapperBuilder xmlMapperBuilder = new XmlMapperBuilder(configuration); xmlMapperBuilder.parse(resourceAsSteam); } return configuration; } }
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"); //解析select|insert|update|delete標籤 List<Element> elementList = rootElement.selectNodes("//select|insert|update|delete"); for (Element element : elementList) { String type= element.getName(); String id = element.attributeValue("id"); String resultType = element.attributeValue("resultType"); String paramterType = element.attributeValue("paramterType"); String sqlText = element.getTextTrim(); MappedStatement mappedStatement = new MappedStatement(); mappedStatement.setId(id); mappedStatement.setResultType(resultType); mappedStatement.setParameterType(paramterType); mappedStatement.setSql(sqlText); mappedStatement.setType(type); String key = namespace+"."+id; configuration.getMappedStatementMap().put(key,mappedStatement); } } }
sqlSession
public class DefaultSqlSession implements SqlSession { private Configuration configuration; public DefaultSqlSession(Configuration configuration) { this.configuration = configuration; } @Override public <E> List<E> selectList(String statementid, Object... params) throws Exception { //將要去完成對simpleExecutor裡的query方法的呼叫 SimpleExecutor simpleExecutor = new SimpleExecutor(); MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementid); List<Object> list = simpleExecutor.query(configuration, mappedStatement, params); return (List<E>) list; } @Override public <T> T selectOne(String statementid, Object... params) throws Exception { List<Object> objects = selectList(statementid, params); if(objects.size()==1){ return (T) objects.get(0); }else { throw new RuntimeException("查詢結果為空或者返回結果過多"); } } @Override public boolean update(String statementId, Object... params) throws Exception { //將要去完成對simpleExecutor裡的query方法的呼叫 SimpleExecutor simpleExecutor = new SimpleExecutor(); MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementId); return simpleExecutor.update(configuration, mappedStatement, params); } @Override public <T> T getMapper(Class<?> mapperClass) { // 使用JDK動態代理來為Dao介面生成代理物件，並返回 Object proxyInstance = Proxy.newProxyInstance(DefaultSqlSession.class.getClassLoader(), new Class[]{mapperClass}, new InvocationHandler() { @Override public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { // 底層都還是去執行JDBC程式碼 //根據不同情況，來呼叫selctList或者selectOne // 準備引數 1：statmentid :sql語句的唯一標識：namespace.id= 介面全限定名.方法名 String methodName = method.getName(); String className = method.getDeclaringClass().getName(); String statementId = className+"."+methodName; //獲取方法型別是select還是增刪改 String type = configuration.getMappedStatementMap().get(statementId).getType(); // 準備引數2：params:args if ("select".equals(type)){ // 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> objects = selectList(statementId, args); return objects; } return selectOne(statementId,args); }else { //返回值型別為void則表示是增刪改操作 return update(statementId,args); } } }); return (T) proxyInstance; } }
public class SqlSessionFactoryBuilder { public SqlSessionFactory build(InputStream in) throws DocumentException, PropertyVetoException { // 第一：使用dom4j解析配置檔案，將解析出來的內容封裝到Configuration中 XmlConfigBuilder xmlConfigBuilder = new XmlConfigBuilder(); Configuration configuration = xmlConfigBuilder.parseConfig(in); // 第二：建立sqlSessionFactory物件：工廠類：生產sqlSession:會話物件 DefaultSqlSessionFactory defaultSqlSessionFactory = new DefaultSqlSessionFactory(configuration); return defaultSqlSessionFactory; } }
public class DefaultSqlSessionFactory implements SqlSessionFactory { private Configuration configuration; public DefaultSqlSessionFactory(Configuration configuration) { this.configuration = configuration; } @Override public SqlSession openSession() { return new DefaultSqlSession(configuration); } }
public class SimpleExecutor implements Executor { @Override public <E> List<E> query(Configuration configuration, MappedStatement mappedStatement, Object... params) throws Exception { // 獲取資料庫連線 PreparedStatement preparedStatement = connectByJdbc(configuration, mappedStatement, params); // 執行sql ResultSet resultSet = preparedStatement.executeQuery(); String resultType = mappedStatement.getResultType(); Class<?> resultTypeClass = getClassType(resultType); ArrayList<Object> objects = new ArrayList<>(); // 封裝返回結果集 while (resultSet.next()){ Object o =resultTypeClass.newInstance(); //元資料 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); } objects.add(o); } return (List<E>) objects; } @Override public boolean update(Configuration configuration, MappedStatement mappedStatement, Object... params) throws Exception{ // 獲取資料庫連線 PreparedStatement preparedStatement = connectByJdbc(configuration, mappedStatement, params); // 執行sql return preparedStatement.execute(); } //使用jdbc進行資料庫連線 private PreparedStatement connectByJdbc(Configuration configuration, MappedStatement mappedStatement, Object... params) throws Exception { // 1. 註冊驅動，獲取連線 Connection connection = configuration.getDataSource().getConnection(); // 2. 獲取sql語句 : 將#｛｝轉換成？佔位符 ，轉換的過程中，還需要對#{}裡面的值進行解析儲存 String sql = mappedStatement.getSql(); BoundSql boundSql = getBoundSql(sql); // 3.獲取預處理物件：preparedStatement PreparedStatement preparedStatement = connection.prepareStatement(boundSql.getSqlText()); // 4. 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); //暴力訪問 declaredField.setAccessible(true); Object o = declaredField.get(params[0]); preparedStatement.setObject(i+1,o); } return preparedStatement; } 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#{}裡面的值進行儲存 * @param sql * @return */ private BoundSql getBoundSql(String sql) { //標記處理類：配置標記解析器來完成對佔位符的解析處理工作 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; } }
解析類
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 * 該方法主要實現了配置檔案、指令碼等片段中佔位符的解析、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，預設不是佔位符，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變數中佔位符對應的變數名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轉義字元，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轉義字元時 // 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 {//不存在轉義字元，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?作為佔位符 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 ParameterMappingTokenHandler implements TokenHandler { private List<ParameterMapping> parameterMappings = new ArrayList<ParameterMapping>(); // context是引數名稱 #{id} #{username} @Override 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; } }
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; } }
Test
@Test public void test() throws Exception { InputStream resourceAsSteam = Resources.getResourceAsSteam("sqlMapConfig.xml"); SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsSteam); SqlSession sqlSession = sqlSessionFactory.openSession(); //呼叫 User user = new User(); user.setId(1); user.setUsername("lucy"); IUserDao userDao = sqlSession.getMapper(IUserDao.class); List<User> all = userDao.findAll(); for (User user1 : all) { System.out.println(user1); } } @Test public void testAdd() throws Exception { InputStream resourceAsSteam = Resources.getResourceAsSteam("sqlMapConfig.xml"); SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsSteam); SqlSession sqlSession = sqlSessionFactory.openSession(); //呼叫 User user = new User(); user.setId(3); user.setUsername("zhangsan"); user.setPassword("123"); user.setBirthday("1999-02-02"); IUserDao userDao = sqlSession.getMapper(IUserDao.class); userDao.addUser(user); }