前不久在研究Datax，需要实现Oracle增加更新，因为当前OracleWriter和MysqlWriter不同，不支持配置writeMode参数。

参考其它博主的步骤，对Datax二次开发，亲测有效，步骤如下：

一、修改OracleWriter.java

删除限制

二、修改WriterUtil.java

添加oracle数据插入类型转换

   public static String getWriteTemplate(List<String> columnHolders, List<String> valueHolders, String writeMode, DataBaseType dataBaseType, boolean forceUseUpdate) {
        boolean isWriteModeLegal = writeMode.trim().toLowerCase().startsWith("insert")
                || writeMode.trim().toLowerCase().startsWith("replace")
                || writeMode.trim().toLowerCase().startsWith("update");

        if (!isWriteModeLegal) {
            throw DataXException.asDataXException(DBUtilErrorCode.ILLEGAL_VALUE,
                    String.format("您所配置的 writeMode:%s 错误. 因为DataX 目前仅支持replace,update 或 insert 方式. 请检查您的配置并作出修改.", writeMode));
        }
        // && writeMode.trim().toLowerCase().startsWith("replace")
        String writeDataSqlTemplate;
        if (forceUseUpdate ||
                ((dataBaseType == DataBaseType.MySql || dataBaseType == DataBaseType.Tddl) && writeMode.trim().toLowerCase().startsWith("update"))
                ) {
            //update只在mysql下使用

            writeDataSqlTemplate = new StringBuilder()
                    .append("INSERT INTO %s (").append(StringUtils.join(columnHolders, ","))
                    .append(") VALUES(").append(StringUtils.join(valueHolders, ","))
                    .append(")")
                    .append(onDuplicateKeyUpdateString(columnHolders))
                    .toString();
        } else {
            // Oracle update语句生成
            if (dataBaseType == DataBaseType.Oracle && writeMode.trim().toLowerCase().startsWith("update")) {
                writeDataSqlTemplate = new StringBuilder()
                        .append(onMergeIntoDoString(writeMode, columnHolders, valueHolders))
                        .append("INSERT (")
                        .append(StringUtils.join(columnHolders, ","))
                        .append(") VALUES(").append(StringUtils.join(valueHolders, ","))
                        .append(")").toString();
            } else {
                if (writeMode.trim().toLowerCase().startsWith("update")) {
                    writeMode = "replace";
                }
                writeDataSqlTemplate = new StringBuilder().append(writeMode)
                        .append(" INTO %s (").append(StringUtils.join(columnHolders, ","))
                        .append(") VALUES(").append(StringUtils.join(valueHolders, ","))
                        .append(")").toString();
            }
        }

        return writeDataSqlTemplate;
    }

增加onMergeIntoDoString方法

   // 新增方法,支持oracle update增量写数据,生成MERGE INTO语句
    public static String onMergeIntoDoString(String merge, List<String> columnHolders, List<String> valueHolders) {
        String[] sArray = getStrings(merge);
        StringBuilder sb = new StringBuilder();
        sb.append("MERGE INTO %s A USING ( SELECT ");

        boolean first = true;
        boolean first1 = true;
        StringBuilder str = new StringBuilder();
        StringBuilder update = new StringBuilder();
        for (String columnHolder : columnHolders) {
            if (Arrays.asList(sArray).contains(columnHolder)) {
                if (!first) {
                    sb.append(",");
                    str.append(" AND ");
                } else {
                    first = false;
                }
                str.append("TMP.").append(columnHolder);
                sb.append("?");
                str.append(" = ");
                sb.append(" AS ");
                str.append("A.").append(columnHolder);
                sb.append(columnHolder);
            }
        }

        for (String columnHolder : columnHolders) {
            if (!Arrays.asList(sArray).contains(columnHolder)) {
                if (!first1) {
                    update.append(",");
                } else {
                    first1 = false;
                }
                update.append(columnHolder);
                update.append(" = ");
                update.append("?");
            }
        }

        sb.append(" FROM DUAL ) TMP ON (");
        sb.append(str);
        sb.append(" ) WHEN MATCHED THEN UPDATE SET ");
        sb.append(update);
        sb.append(" WHEN NOT MATCHED THEN ");
        LOG.info("update sql => {}", sb.toString());
        return sb.toString();
    }
    // 解析".json"配置中"writeMode"参数
    public static String[] getStrings(String merge) {
        merge = merge.replace("update", "");
        merge = merge.replace("(", "");
        merge = merge.replace(")", "");
        merge = merge.replace(" ", "");
        return merge.split(",");
    }

三、CommonRdbmsWriter

      public void startWriteWithConnection(RecordReceiver recordReceiver, TaskPluginCollector taskPluginCollector, Connection connection) {
            this.taskPluginCollector = taskPluginCollector;
            // 以下代码为支持oracl update增量写数据
            List<String> columns = new ArrayList<String>();
            List<String> columnsOne = new ArrayList<String>();
            List<String> columnsTwo = new ArrayList<String>();
            if (this.dataBaseType == DataBaseType.Oracle && this.writeMode.trim().toLowerCase().startsWith("update")) {
                String merge = this.writeMode;
                String[] sArray = WriterUtil.getStrings(merge);
                int size = this.columns.size();
                int i = 0;
                for (int j = 0; j < size; j++) {
                    if (Arrays.asList(sArray).contains(this.columns.get(j))) {
                        columnsOne.add(this.columns.get(j));
                    }
                }
                for (int j = 0; j < size; j++) {
                    if (!Arrays.asList(sArray).contains(this.columns.get(j))) {
                        columnsTwo.add(this.columns.get(j));
                    }
                }
                for (String column : columnsOne) {
                    columns.add(i, column);
                    i++;
                }
                for (String column : columnsTwo) {
                    columns.add(i, column);
                    i++;
                }
                columns.addAll(this.columns);
                this.resultSetMetaData = DBUtil.getColumnMetaData(connection,
                        this.table, StringUtils.join(columns, ","));
            } else {
                this.resultSetMetaData = DBUtil.getColumnMetaData(connection,
                        this.table, StringUtils.join(this.columns, ","));
            }
            // oracal update增量写数据支持代码。over

            // 用于写入数据的时候的类型根据目的表字段类型转换
//            this.resultSetMetaData = DBUtil.getColumnMetaData(connection,
//                    this.table, StringUtils.join(columns, ","));
            // 写数据库的SQL语句
            calcWriteRecordSql();

            List<Record> writeBuffer = new ArrayList<Record>(this.batchSize);
            int bufferBytes = 0;
            try {
                Record record;
                while ((record = recordReceiver.getFromReader()) != null) {
                    if (record.getColumnNumber() != this.columnNumber) {
                        // 源头读取字段列数与目的表字段写入列数不相等，直接报错
                        throw DataXException
                                .asDataXException(
                                        DBUtilErrorCode.CONF_ERROR,
                                        String.format(
                                                "列配置信息有错误. 因为您配置的任务中，源头读取字段数:%s 与 目的表要写入的字段数:%s 不相等. 请检查您的配置并作出修改.",
                                                record.getColumnNumber(),
                                                this.columnNumber));
                    }

                    writeBuffer.add(record);
                    bufferBytes += record.getMemorySize();

                    if (writeBuffer.size() >= batchSize || bufferBytes >= batchByteSize) {
                        doBatchInsert(connection, writeBuffer);
                        writeBuffer.clear();
                        bufferBytes = 0;
                    }
                }
                if (!writeBuffer.isEmpty()) {
                    doBatchInsert(connection, writeBuffer);
                    writeBuffer.clear();
                    bufferBytes = 0;
                }
            } catch (Exception e) {
                throw DataXException.asDataXException(
                        DBUtilErrorCode.WRITE_DATA_ERROR, e);
            } finally {
                writeBuffer.clear();
                bufferBytes = 0;
                DBUtil.closeDBResources(null, null, connection);
            }
        }

              protected void doBatchInsert(Connection connection, List<Record> buffer)
                throws SQLException {
            PreparedStatement preparedStatement = null;
            try {
                connection.setAutoCommit(false);
                preparedStatement = connection
                        .prepareStatement(this.writeRecordSql);

                // 以下代码为支持oracle update增量写数据
                LOG.info("For {}",this.writeMode + "data to Oracle");
                if (this.dataBaseType == DataBaseType.Oracle && this.writeMode.trim().toLowerCase().startsWith("update")) {
                    String merge = this.writeMode;
                    String[] sArray = WriterUtil.getStrings(merge);
                    for (Record record : buffer) {
                        List<Column> recordOne = new ArrayList<Column>();
                        for (int j = 0; j < this.columns.size(); j++) {
                            if (Arrays.asList(sArray).contains(this.columns.get(j))) {
                                recordOne.add(record.getColumn(j));
                            }
                        }
                        for (int j = 0; j < this.columns.size(); j++) {
                            if (!Arrays.asList(sArray).contains(this.columns.get(j))) {
                                recordOne.add(record.getColumn(j));
                            }
                        }
                        for (int j = 0; j < this.columns.size(); j++) {
                            recordOne.add(record.getColumn(j));
                        }
                        for (int j = 0; j < recordOne.size(); j++) {
                            record.setColumn(j, recordOne.get(j));
                        }
                        preparedStatement = fillPreparedStatement(
                                preparedStatement, record, this.writeMode);
                        preparedStatement.addBatch();
                    }
                } else {
                    for (Record record : buffer) {
                        preparedStatement = fillPreparedStatement(
                                preparedStatement, record);
                        preparedStatement.addBatch();
                    }
                }
                // 支持oracle update增量写数据代码。over
                preparedStatement.executeBatch();
                connection.commit();
            } catch (SQLException e) {
                LOG.warn("回滚此次写入, 采用每次写入一行方式提交. 因为:" + e.getMessage());
                connection.rollback();
                doOneInsert(connection, buffer);
            } catch (Exception e) {
                throw DataXException.asDataXException(
                        DBUtilErrorCode.WRITE_DATA_ERROR, e);
            } finally {
                DBUtil.closeDBResources(preparedStatement, null);
            }
        }
// 为支持oracle update
        protected PreparedStatement fillPreparedStatement(PreparedStatement preparedStatement, Record record, String writeMode)
                throws SQLException {
            for (int i = 0; i < record.getColumnNumber(); i++) {
                int columnSqltype = this.resultSetMetaData.getMiddle().get(i);
                preparedStatement = fillPreparedStatementColumnType(preparedStatement, i, columnSqltype, record.getColumn(i));
            }

            return preparedStatement;
        }

以上配置的底层实现SQL，是Oracle 的MERGE语句。

MERGE INTO T_TEST A USING ( SELECT ? AS ID,? AS USERNAME FROM DUAL ) TMP 
ON (TMP.ID = A.ID AND TMP.USERNAME = A.USERNAME ) 
WHEN MATCHED THEN UPDATE SET AGE = ? 
WHEN NOT MATCHED THEN INSERT (ID,USERNAME,AGE) VALUES(?,?,?)