入口：PreparedStatementHandler#parameterize方法

设置PreparedStatement的参数

 @Override
  public void parameterize(Statement statement) throws SQLException {
    // 通过ParameterHandler处理参数
    parameterHandler.setParameters((PreparedStatement) statement);
  }

• DefaultParameterHandler#setParameters

  设置参数

      @Override
    public void setParameters(PreparedStatement ps) {
        ErrorContext.instance().activity("setting parameters").object(mappedStatement.getParameterMap().getId());
        // 获取要设置的参数映射信息
        List<ParameterMapping> parameterMappings = boundSql.getParameterMappings();
        if (parameterMappings != null) {
            for (int i = 0; i < parameterMappings.size(); i++) {
                ParameterMapping parameterMapping = parameterMappings.get(i);
                // 只处理入参
                if (parameterMapping.getMode() != ParameterMode.OUT) {
                    Object value;
                    // 获取属性名称
                    String propertyName = parameterMapping.getProperty();
                    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())) {
                        value = parameterObject;
                    } else {
                        MetaObject metaObject = configuration.newMetaObject(parameterObject);
                        value = metaObject.getValue(propertyName);
                    }
                    // 获取每个参数的类型处理器，去设置入参和获取返回值
                    TypeHandler typeHandler = parameterMapping.getTypeHandler();
                    // 获取每个参数的JdbcType
                    JdbcType jdbcType = parameterMapping.getJdbcType();
                    if (value == null && jdbcType == null) {
                        jdbcType = configuration.getJdbcTypeForNull();
                    }
                    try {
                        // 给PreparedStatement设置参数
                        typeHandler.setParameter(ps, i + 1, value, jdbcType);
                    } catch (TypeException e) {
                        throw new TypeException(
                                "Could not set parameters for mapping: " + parameterMapping + ". Cause: " + e, e);
                    } catch (SQLException e) {
                        throw new TypeException(
                                "Could not set parameters for mapping: " + parameterMapping + ". Cause: " + e, e);
                    }
                }
            }
        }
    }

• BaseTypeHandler#setParameter

  给PreparedStatement设置参数

@Override
    public void setParameter(PreparedStatement ps, int i, T parameter, JdbcType jdbcType) throws SQLException {
        if (parameter == null) {
            if (jdbcType == null) {
                throw new TypeException(
                        "JDBC requires that the JdbcType must be specified for all nullable parameters.");
            }
            try {
                ps.setNull(i, jdbcType.TYPE_CODE);
            } catch (SQLException e) {
                throw new TypeException("Error setting null for parameter #" + i + " with JdbcType " + jdbcType + " . "
                        + "Try setting a different JdbcType for this parameter or a different jdbcTypeForNull configuration property. "
                        + "Cause: " + e, e);
            }
        } else {
            try {
                // 通过PreparedStatement的API去设置非空参数
                setNonNullParameter(ps, i, parameter, jdbcType);
            } catch (Exception e) {
                throw new TypeException("Error setting non null for parameter #" + i + " with JdbcType " + jdbcType
                        + " . "
                        + "Try setting a different JdbcType for this parameter or a different configuration property. "
                        + "Cause: " + e, e);
            }
        }
    }

• xxxTypeHandler#setNonNullParameter

  通过PreparedStatement的API去设置非空参数
  例如：ArrayTypeHandler

@Override
  public void setNonNullParameter(PreparedStatement ps, int i, Object parameter, JdbcType jdbcType) throws SQLException {
    ps.setArray(i, (Array) parameter);
  }