The processing flow of insert method, update method and delete method in java (Part 2)-javaTutorial-php.cn

Configuration’s newStatementHandler analysis

SimpleExecutor’s doUpdate method has been analyzed above:

 1 public int doUpdate(MappedStatement ms, Object parameter) throws SQLException { 2     Statement stmt = null; 3     try { 4       Configuration configuration = ms.getConfiguration(); 5       StatementHandler handler = configuration.newStatementHandler(this, ms, parameter, RowBounds.DEFAULT, null, null); 6       stmt = prepareStatement(handler, ms.getStatementLog()); 7       return handler.update(stmt); 8     } finally { 9       closeStatement(stmt);10     }11 }

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When I re-read the newStatementHandler method in line 5 in the past two days, I found that the method analyzed above in this method is too simple. Let’s go through the newStatementHandler method of Configuration. The implementation of the method is:

1 public StatementHandler newStatementHandler(Executor executor, MappedStatement mappedStatement, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) {2     StatementHandler statementHandler = new RoutingStatementHandler(executor, mappedStatement, parameterObject, rowBounds, resultHandler, boundSql);3     statementHandler = (StatementHandler) interceptorChain.pluginAll(statementHandler);4     return statementHandler;5 }

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The 3rd line of code is for adding a plug-in, which is nothing interesting. Take a look at the 2nd line of code. What is actually instantiated by the StatementHandler interface is RoutingStatementHandler, and the construction method The implementation is:

 1 public RoutingStatementHandler(Executor executor, MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) { 2  3     switch (ms.getStatementType()) { 4       case STATEMENT: 5         delegate = new SimpleStatementHandler(executor, ms, parameter, rowBounds, resultHandler, boundSql); 6         break; 7       case PREPARED: 8         delegate = new PreparedStatementHandler(executor, ms, parameter, rowBounds, resultHandler, boundSql); 9         break;10       case CALLABLE:11         delegate = new CallableStatementHandler(executor, ms, parameter, rowBounds, resultHandler, boundSql);12         break;13       default:14         throw new ExecutorException("Unknown statement type: " + ms.getStatementType());15     }16 17 }

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RoutingStatementHandler is also an implementation of the decorator pattern, which implements the StatementHandler interface and holds the StatementHandler interface reference delegate. The StatementType here is PREPARED, so the judgment on line 7 is executed to instantiate PreparedStatementHandler. The instantiation process is:

 1 protected BaseStatementHandler(Executor executor, MappedStatement mappedStatement, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) { 2     this.configuration = mappedStatement.getConfiguration(); 3     this.executor = executor; 4     this.mappedStatement = mappedStatement; 5     this.rowBounds = rowBounds; 6  7     this.typeHandlerRegistry = configuration.getTypeHandlerRegistry(); 8     this.objectFactory = configuration.getObjectFactory(); 9 10     if (boundSql == null) { // issue #435, get the key before calculating the statement11       generateKeys(parameterObject);12       boundSql = mappedStatement.getBoundSql(parameterObject);13     }14 15     this.boundSql = boundSql;16 17     this.parameterHandler = configuration.newParameterHandler(mappedStatement, parameterObject, boundSql);18     this.resultSetHandler = configuration.newResultSetHandler(executor, mappedStatement, rowBounds, parameterHandler, resultHandler, boundSql);19 }

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The focus here is BoundSql , which can be obtained through MappedStatement. Several important contents are stored in BoundSql:

The parameter object itself
Parameter list
SQL statement to be executed

Some secondary development frameworks based on MyBatis usually get the SQL statements in BoundSql, modify them and reset them into BoundSql.

Generate Statement

##The process of generating Connection has been written above. This article continues Look, first let’s post the prepareStatement method of SimpleExecutor again:

1 private Statement prepareStatement(StatementHandler handler, Log statementLog) throws SQLException {2     Statement stmt;3     Connection connection = getConnection(statementLog);4     stmt = handler.prepare(connection, transaction.getTimeout());5     handler.parameterize(stmt);6     return stmt;7 }

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Then there is the code in line 4, which generates Statement. The code in line 4 is implemented as:

  Statement prepare(Connection connection, Integer transactionTimeout)

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delegate The above is the decorated role in the decorator mode. Its interface type is StatementHandler and its real type is PreparedStatementHandler. This has been analyzed at the beginning. Take a look at the prepare method implementation:

 1 public Statement prepare(Connection connection, Integer transactionTimeout) throws SQLException { 2     ErrorContext.instance().sql(boundSql.getSql()); 3     Statement statement = null; 4     try { 5       statement = instantiateStatement(connection); 6       setStatementTimeout(statement, transactionTimeout); 7       setFetchSize(statement); 8       return statement; 9     } catch (SQLException e) {10       closeStatement(statement);11       throw e;12     } catch (Exception e) {13       closeStatement(statement);14       throw new ExecutorException("Error preparing statement.  Cause: " + e, e);15     }16 }

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The code in line 6 sets the query timeout, and the code in line 7 sets the received data size. I won’t follow up and look at it. Let’s look at the implementation of the instantiateStatement method in line 6:

 1 protected Statement instantiateStatement(Connection connection) throws SQLException { 2     String sql = boundSql.getSql(); 3     if (mappedStatement.getKeyGenerator() instanceof Jdbc3KeyGenerator) { 4       String[] keyColumnNames = mappedStatement.getKeyColumns(); 5       if (keyColumnNames == null) { 6         return connection.prepareStatement(sql, PreparedStatement.RETURN_GENERATED_KEYS); 7       } else { 8         return connection.prepareStatement(sql, keyColumnNames); 9       }10     } else if (mappedStatement.getResultSetType() != null) {11       return connection.prepareStatement(sql, mappedStatement.getResultSetType().getValue(), ResultSet.CONCUR_READ_ONLY);12     } else {13       return connection.prepareStatement(sql);14     }15 }

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Line 2, get the real SQL statement from boundSql, The first part has already been analyzed. After getting the SQL statement, execute the judgment on lines 3 and 5. Here is the code we are familiar with to get the Statement through Connection. PreparedStatement is obtained through the prepareStatement method. Its true type is com.mysql.jdbc.JDBC4PreparedStatement, which is Subclass of PreparedStatement.

Statement parameter setting

After obtaining the Statement, the next step is to set the parameters. , look at the code for setting parameters, or go back to the prepareStatement method of SimpleExecutor:

1 private Statement prepareStatement(StatementHandler handler, Log statementLog) throws SQLException {2     Statement stmt;3     Connection connection = getConnection(statementLog);4     stmt = handler.prepare(connection, transaction.getTimeout());5     handler.parameterize(stmt);6     return stmt;7 }

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and the code on line 5:

 1 public void parameterize(Statement statement) throws SQLException { 2     parameterHandler.setParameters((PreparedStatement) statement); 3 }

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Continue with the code in line 2:

 1 public void setParameters(PreparedStatement ps) { 2     ErrorContext.instance().activity("setting parameters").object(mappedStatement.getParameterMap().getId()); 3     List<ParameterMapping> parameterMappings = boundSql.getParameterMappings(); 4     if (parameterMappings != null) { 5       for (int i = 0; i < parameterMappings.size(); i++) { 6         ParameterMapping parameterMapping = parameterMappings.get(i); 7         if (parameterMapping.getMode() != ParameterMode.OUT) { 8           Object value; 9           String propertyName = parameterMapping.getProperty();10           if (boundSql.hasAdditionalParameter(propertyName)) { // issue #448 ask first for additional params11             value = boundSql.getAdditionalParameter(propertyName);12           } else if (parameterObject == null) {13             value = null;14           } else if (typeHandlerRegistry.hasTypeHandler(parameterObject.getClass())) {15             value = parameterObject;16           } else {17             MetaObject metaObject = configuration.newMetaObject(parameterObject);18             value = metaObject.getValue(propertyName);19           }20           TypeHandler typeHandler = parameterMapping.getTypeHandler();21           JdbcType jdbcType = parameterMapping.getJdbcType();22           if (value == null && jdbcType == null) {23             jdbcType = configuration.getJdbcTypeForNull();24           }25           try {26             typeHandler.setParameter(ps, i + 1, value, jdbcType);27           } catch (TypeException e) {28             throw new TypeException("Could not set parameters for mapping: " + parameterMapping + ". Cause: " + e, e);29           } catch (SQLException e) {30             throw new TypeException("Could not set parameters for mapping: " + parameterMapping + ". Cause: " + e, e);31           }32         }33       }34     }35 }

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最终执行的是第26行的代码，从26行的代码我们可以知道，参数设置到最后都是通过参数的TypeHandler来执行的，JDBC为我们预定义了很多TypeHandler，比如int值的TypeHandler就是IntegerTypeHandler，当然我们也可以定义自己的TypeHandler，通常来说继承BaseTypeHandler就可以了。

但是在此之前，会获取到Statement（setParameters方法形参）、占位符位置号（for循环的遍历参数i）、参数值（通过属性名获取）与jdbcType（配置在配置文件中，默认为null），最终执行TypeHandler的setParameters方法，这是BaseTypeHandler中的一个方法：

 1 public void setParameter(PreparedStatement ps, int i, T parameter, JdbcType jdbcType) throws SQLException { 2     if (parameter == null) { 3       if (jdbcType == null) { 4         throw new TypeException("JDBC requires that the JdbcType must be specified for all nullable parameters."); 5       } 6       try { 7         ps.setNull(i, jdbcType.TYPE_CODE); 8       } catch (SQLException e) { 9         throw new TypeException("Error setting null for parameter #" + i + " with JdbcType " + jdbcType + " . " +10                 "Try setting a different JdbcType for this parameter or a different jdbcTypeForNull configuration property. " +11                 "Cause: " + e, e);12       }13     } else {14       try {15         setNonNullParameter(ps, i, parameter, jdbcType);16       } catch (Exception e) {17         throw new TypeException("Error setting non null for parameter #" + i + " with JdbcType " + jdbcType + " . " +18                 "Try setting a different JdbcType for this parameter or a different configuration property. " +19                 "Cause: " + e, e);20       }21     }22 }

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这里的参数不为null，走13行的else，执行setNonNullParameter方法，这是IntegerTypeHandler中的一个方法：

   setNonNullParameter(PreparedStatement ps,

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这里的代码就比较熟悉了，PreparedStatement的setInt方法。

执行更新操作并处理结果

最后一步，执行更新操作并对结果进行处理，回到SimpleExecuto的doUpdate方法：

 1 public int doUpdate(MappedStatement ms, Object parameter) throws SQLException { 2     Statement stmt = null; 3     try { 4       Configuration configuration = ms.getConfiguration(); 5       StatementHandler handler = configuration.newStatementHandler(this, ms, parameter, RowBounds.DEFAULT, null, null); 6       stmt = prepareStatement(handler, ms.getStatementLog()); 7       return handler.update(stmt); 8     } finally { 9       closeStatement(stmt);10     }11 }

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第6行已经准备好了Statement，第7行执行update操作并对结果进行处理并返回：

   update(Statement statement)

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这里的委托delegate前面已经说过了，其真实类型是PreparedStatementHandler，update方法的实现为：

1 public int update(Statement statement) throws SQLException {2     PreparedStatement ps = (PreparedStatement) statement;3     ps.execute();4     int rows = ps.getUpdateCount();5     Object parameterObject = boundSql.getParameterObject();6     KeyGenerator keyGenerator = mappedStatement.getKeyGenerator();7     keyGenerator.processAfter(executor, mappedStatement, ps, parameterObject);8     return rows;9 }

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第3行的execute方法是PreparedStatement中的方法，execute方法执行操作，然后第4行通过getUpdateCount()方法获取本次操作更新了几条数据，作为最终的值返回给用户。

第5行的代码通过BoundSql获取参数对象，这里是MailDO对象，因为我们知道在插入场景下，开发者是有这种需求的，需要返回插入的主键id，此时会将主键id设置到MailDO中。

第6行的代码通过MappedStatement获取KeyGenerator，一个主键生成器。

第7行的代码做了一个操作完毕的后置处理：

<span style="color: #008080"> 1</span> <span style="color: #0000ff">public</span> <span style="color: #0000ff">void</span><span style="color: #000000"> processAfter(Executor executor, MappedStatement ms, Statement stmt, Object parameter) {</span><span style="color: #008080"> 2</span> <span style="color: #000000">    processBatch(ms, stmt, getParameters(parameter));</span><span style="color: #008080"> 3</span> <span style="color: #000000">}</span><span style="color: #008080"><br/></span>

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首先将对象包装成集合类型，然后跟第2行的代码processBatch方法：

 1 public void processBatch(MappedStatement ms, Statement stmt, Collection<Object> parameters) { 2     ResultSet rs = null; 3     try { 4       rs = stmt.getGeneratedKeys(); 5       final Configuration configuration = ms.getConfiguration(); 6       final TypeHandlerRegistry typeHandlerRegistry = configuration.getTypeHandlerRegistry(); 7       final String[] keyProperties = ms.getKeyProperties(); 8       final ResultSetMetaData rsmd = rs.getMetaData(); 9       TypeHandler<?>[] typeHandlers = null;10       if (keyProperties != null && rsmd.getColumnCount() >= keyProperties.length) {11         for (Object parameter : parameters) {12           // there should be one row for each statement (also one for each parameter)13           if (!rs.next()) {14             break;15           }16           final MetaObject metaParam = configuration.newMetaObject(parameter);17           if (typeHandlers == null) {18             typeHandlers = getTypeHandlers(typeHandlerRegistry, metaParam, keyProperties, rsmd);19           }20           populateKeys(rs, metaParam, keyProperties, typeHandlers);21         }22       }23     } catch (Exception e) {24       throw new ExecutorException("Error getting generated key or setting result to parameter object. Cause: " + e, e);25     } finally {26       if (rs != null) {27         try {28           rs.close();29         } catch (Exception e) {30           // ignore31         }32       }33     }34 }

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简单说这里就是遍历集合，通过JDBC4PreparedStatement的getGeneratedKeys获取ResultSet，然后从ResultSet中使用getLong方法获取生成的主键，设置到MailDO中。完成整个操作。

最后，本文演示的是insert数据的update方法流程，前文已经说过insert、update、delete在MyBatis中都是一样的，因此update、delete也是一样的操作，这里就不再赘述了。

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