简化流程图

PreparedStatement

设置如果是PreparedStatement，则最终都是调用PreparedStatement的setXXX方法

PreparedStatement pstmt = con.prepareStatement("UPDATE EMPLOYEES  SET AGE=?  WHERE ID = ?");                                  pstmt.setInt(1, 20);pstmt.setInt(2, 110592);

注意第１个参数是１（parameterIndex the first parameter is 1, the second is 2, ...）

PreparedStatement相关方法：

BoundSql

TypeHandler

这里只关注setParameter函数

public interface TypeHandler
   
     {  void setParameter(PreparedStatement ps, int i, T parameter, JdbcType jdbcType) throws SQLException;  .......................}

如果javaType=UnknownTypeHandler ，并且未指定JdbcType，会根据parameter的类型，推断出对应的TypeHandler，比如，参数是String类型的，会推断StringTypeHandler

public class UnknownTypeHandler extends BaseTypeHandler

StringTypeHandler

public class StringTypeHandler extends BaseTypeHandler
   
     {  @Override  public void setNonNullParameter(PreparedStatement ps, int i, String parameter, JdbcType jdbcType)      throws SQLException {    ps.setString(i, parameter);  }}

DefaultParameterHandler

public void setParameters(PreparedStatement ps) {	ErrorContext.instance().activity("setting parameters").object(mappedStatement.getParameterMap().getId());	List
   
     parameterMappings = boundSql.getParameterMappings();	if (parameterMappings != null) {	  for (int i = 0; i < parameterMappings.size(); i++) {		ParameterMapping parameterMapping = parameterMappings.get(i); // 具体的第几个参数-详细信息		if (parameterMapping.getMode() != ParameterMode.OUT) { // IN or INOUT 才处理		  Object value;		  String propertyName = parameterMapping.getProperty(); //得到入参的属性名 比如username、a.id 等 #{id} #{a.id}		  if (boundSql.hasAdditionalParameter(propertyName)) { // issue #448 ask first for additional params			value = boundSql.getAdditionalParameter(propertyName);		  } else if (parameterObject == null) {			value = null;		  } else if (typeHandlerRegistry.hasTypeHandler(parameterObject.getClass())) { // 单个参数的类型，如果在typeHandlerRegistry里注册了，value就是=parameterObject			value = parameterObject; // 单个参数情况下，并且在typeHandlerRegistry里注册了parameterObject的类型，则value就是=parameterObject		  } else {			MetaObject metaObject = configuration.newMetaObject(parameterObject); // 一般都是走这里的			value = metaObject.getValue(propertyName); // 通过metaObject得到具体要设置pos的值  first parameter is 1, the second is 2		  }		  TypeHandler typeHandler = parameterMapping.getTypeHandler(); // 未指定是UnknownTypeHandler		  JdbcType jdbcType = parameterMapping.getJdbcType();		  if (value == null && jdbcType == null) {			jdbcType = configuration.getJdbcTypeForNull();		  }		  try {			typeHandler.setParameter(ps, i + 1, value, jdbcType);  // first parameter is 1, the second is 2		  } catch (TypeException | SQLException e) {			throw new TypeException("Could not set parameters for mapping: " + parameterMapping + ". Cause: " + e, e);		  }		}	  }	}}