alibaba/DataX · error · RuntimeException

dx_filter para 2 can't be null

Error message

dx_filter para 2 can't be null

What it means

The dx_filter transformer rejects an empty/null comparison value: StringUtils.isEmpty(paras[2]) throws RuntimeException('dx_filter para 2 can't be null'), rewrapped as TRANSFORMER_ILLEGAL_PARAMETER. Filtering always needs a concrete right-hand value to compare against; there is no 'compare with empty' mode.

Source

Thrown at core/src/main/java/com/alibaba/datax/core/transport/transformer/FilterTransformer.java:36

    @Override
    public Record evaluate(Record record, Object... paras) {

        int columnIndex;
        String code;
        String value;

        try {
            if (paras.length != 3) {
                throw new RuntimeException("dx_filter paras must be 3");
            }

            columnIndex = (Integer) paras[0];
            code = (String) paras[1];
            value = (String) paras[2];

            if (StringUtils.isEmpty(value)) {
                throw new RuntimeException("dx_filter para 2 can't be null");
            }
        } catch (Exception e) {
            throw DataXException.asDataXException(TransformerErrorCode.TRANSFORMER_ILLEGAL_PARAMETER, "paras:" + Arrays.asList(paras).toString() + " => " + e.getMessage());
        }


        Column column = record.getColumn(columnIndex);

        try {

            if (code.equalsIgnoreCase("like")) {
                return doLike(record, value, column);
            } else if (code.equalsIgnoreCase("not like")) {
                return doNotLike(record, value, column);
            } else if (code.equalsIgnoreCase(">")) {
                return doGreat(record, value, column, false);
            } else if (code.equalsIgnoreCase("<")) {
                return doLess(record, value, column, false);

View on GitHub (pinned to 80ec23d5c5)

Solutions

1. Set a concrete comparison value string, e.g. "100" or "beijing".
2. If the filter is optional, remove the whole transformer entry instead of leaving an empty value.
3. Assert non-empty third param in job-generation code.

Example fix

// before
{"name": "dx_filter", "parameter": [2, "=", ""]}

// after
{"name": "dx_filter", "parameter": [2, "=", "active"]}

String value = (String) paras[2];
if (value == null || value.trim().isEmpty()) throw new IllegalArgumentException("dx_filter value must be non-empty");

When it happens

Trigger: Declaring the third parameter as "" or null: {"name":"dx_filter","parameter":[2,">",""]}. Note the length check (error 52) passes because the array has 3 elements — the slot is just empty.

Common situations: Templated job generation that leaves the value blank for optional filters; trailing-comma JSON artifacts producing an empty string.

Related errors

• dx_filter paras must be 3
• CONFIG_ERROR
• dx_digest paras length must be 3
• dx_digest paras index 1 must be md5 or sha1
• dx_digest paras index 2 must be toUpperCase or toLowerCase

AI-assisted analysis of alibaba/DataX@80ec23d5c5 (2026-08-14). Data as JSON: /api/errors/ce724e10c00f3ab4. Report an issue: GitHub.