elastic/elasticsearch · error · IllegalArgumentException

url parameter [{}] has already been set to [{}]

Error message

url parameter [{}] has already been set to [{}]

What it means

Request.addParameter stores query parameters in a map keyed by name and forbids overwriting an existing key, throwing with both the name and the previously-set value. Callers must deliberately set a parameter once; to change it they should build a fresh Request rather than mutate, preventing accidental double-application of filters/params.

Source

Thrown at client/rest/src/main/java/org/elasticsearch/client/Request.java:78

    /**
     * The path of the request (without scheme, host, port, or prefix).
     */
    public String getEndpoint() {
        return endpoint;
    }

    /**
     * Add a query string parameter.
     * @param name the name of the url parameter. Must not be null.
     * @param value the value of the url parameter. If {@code null} then
     *      the parameter is sent as {@code name} rather than {@code name=value}
     * @throws IllegalArgumentException if a parameter with that name has
     *      already been set
     */
    public void addParameter(String name, String value) {
        Objects.requireNonNull(name, "url parameter name cannot be null");
        if (parameters.containsKey(name)) {
            throw new IllegalArgumentException("url parameter [" + name + "] has already been set to [" + parameters.get(name) + "]");
        } else {
            parameters.put(name, value);
        }
    }

    public void addParameters(Map<String, String> paramSource) {
        paramSource.forEach(this::addParameter);
    }

    /**
     * Query string parameters. The returned map is an unmodifiable view of the
     * map in the request so calls to {@link #addParameter(String, String)}
     * will change it.
     */
    public Map<String, String> getParameters() {
        return unmodifiableMap(parameters);
    }

View on GitHub (pinned to db6a809a66)

Solutions

1. Set each parameter at most once; remove the duplicate addParameter call.
2. If overriding is intended, construct a new Request and set the final value, or clear parameters first.
3. Centralize parameter setting in one builder method to avoid scattered duplicate calls.

Example fix

// before
req.addParameter("size", "10");
req.addParameter("size", "50"); // throws
// after
req.addParameter("size", "50"); // set once

// Ensure a param is set exactly once per Request:
if (!req.getParameters().containsKey(name)) {
    req.addParameter(name, value);
} else {
    // build a fresh Request or log a conflict
}

When it happens

Trigger: Calling req.addParameter("size", "10") twice on the same Request instance; calling addParameters(map) where the map contains a key already added via addParameter; chaining helper builders that each set the same param (e.g. 'pretty', 'filter_path').

Common situations: A request builder helper sets 'filter_path' and the caller also sets it; merging two parameter maps that overlap; reusing a Request object across retries and re-adding params.

Related errors

• can't compare DeadHostStates holding different time supplier
• bufferLimit must be greater than 0
• host cannot be null
• cloudId {} must begin with a human readable identifier follo
• cloudId {} did not decode to a cluster identifier correctly

AI-assisted analysis of elastic/elasticsearch@db6a809a66 (2026-08-12). Data as JSON: /api/errors/22d6f032012d99e3. Report an issue: GitHub.