alibaba/DataX · error · RuntimeException

dx_pad paras must be 4

Error message

dx_pad paras must be 4

What it means

The dx_pad transformer requires exactly 4 parameters; any other count throws RuntimeException('dx_pad paras must be 4'), rewrapped as DataXException(TRANSFORMER_ILLEGAL_PARAMETER). Expected paras: columnIndex (Integer), padType ('l'|'r' style left/right), target length (string-parsed Integer), and pad string.

Source

Thrown at core/src/main/java/com/alibaba/datax/core/transport/transformer/PadTransformer.java:30

 * no comments.
 * Created by liqiang on 16/3/4.
 */
public class PadTransformer extends Transformer {
    public PadTransformer() {
        setTransformerName("dx_pad");
    }

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

        int columnIndex;
        String padType;
        int length;
        String padString;

        try {
            if (paras.length != 4) {
                throw new RuntimeException("dx_pad paras must be 4");
            }

            columnIndex = (Integer) paras[0];
            padType = (String) paras[1];
            length = Integer.valueOf((String) paras[2]);
            padString = (String) paras[3];
        } catch (Exception e) {
            throw DataXException.asDataXException(TransformerErrorCode.TRANSFORMER_ILLEGAL_PARAMETER, "paras:" + Arrays.asList(paras).toString() + " => " + e.getMessage());
        }

        Column column = record.getColumn(columnIndex);

        try {
            String oriValue = column.asString();

            //如果字段为空，作为空字符串处理
            if(oriValue==null){
                oriValue = "";

View on GitHub (pinned to 80ec23d5c5)

Solutions

1. Supply exactly 4 params: [columnIndex, padType, lengthAsString, padString], e.g. [0, "l", "5", "0"].
2. Ensure the length parameter is a quoted string in job JSON.
3. Validate transformer blocks with a JSON schema in your job-generation pipeline.

Example fix

// before
{"name": "dx_pad", "parameter": [0, "l", 5]}

// after
{"name": "dx_pad", "parameter": [0, "l", "5", "0"]}

Object[] p = {0, "l", "5", "0"};
if (p.length != 4) throw new IllegalArgumentException("dx_pad needs 4 paras");
Integer.parseInt((String) p[2]); // also validates numeric length

catch (DataXException e) when TRANSFORMER_ILLEGAL_PARAMETER: fail fast, print paras; not retryable.

When it happens

Trigger: Declaring {"name":"dx_pad","parameter":[0,"l","5"]} (3 params) or 5 params in the job transformer block; also fires when paras[2] is not a number, since the catch wraps NumberFormatException with the same code.

Common situations: Omitting the pad string (assuming space default); passing length as a JSON number instead of a string — Integer.valueOf((String) paras[2]) requires a string.

Related errors

• 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
• dx_filter paras must be 3
• dx_filter para 2 can't be null

AI-assisted analysis of alibaba/DataX@80ec23d5c5 (2026-08-14). Data as JSON: /api/errors/1ea6d6774c4bcb26. Report an issue: GitHub.