VS Code Java Input Redirection Guide | Generated by AI

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Question: How to configure input redirection for a Java program in VS Code launch.json (e.g. redirect from file like 1.in)?

Answer:

In VS Code’s launch.json for Java, there are several correct ways to redirect standard input (System.in) from a file. Here are the most commonly used and reliable methods in 2025:

Recommended Method 1 – Using args with < redirection (most popular)

{
    "version": "0.2.0",
    "configurations": [
        {
            "type": "java",
            "name": "Current File (with input redirect)",
            "request": "launch",
            "mainClass": "${file}",
            "args": "< \"${workspaceFolder}/src/main/resources/uva/${problem}/1.in\"",
            "cwd": "${workspaceFolder}"
        }
    ]
}

Note: Use double quotes around the path if it contains spaces.
This is the most widely used method in competitive programming communities.

Method 2 – Using redirector (old style – still works in many setups)

{
    "type": "java",
    "name": "Current File with input file",
    "request": "launch",
    "mainClass": "${file}",
    "redirector": {
        "input": "${workspaceFolder}/src/main/resources/uva/${problem}/1.in"
    }
}

Important:
This format only works if your Java extension supports the redirector attribute (older versions did, newer ones sometimes ignore it or require different syntax).

Method 3 – Cleanest & most reliable in recent VS Code + Java Extension (2024–2026)

{
    "version": "0.2.0",
    "configurations": [
        {
            "type": "java",
            "name": "Launch with input redirection",
            "request": "launch",
            "mainClass": "${file}",
            "args": [
                "<",
                "${workspaceFolder}/src/main/resources/uva/${problem}/1.in"
            ],
            "cwd": "${workspaceFolder}"
        }
    ]
}

This format avoids shell quoting issues on Windows/macOS/Linux.

Bonus: Dynamic problem name using input prompt

{
    "type": "java",
    "name": "UVa - Ask problem number",
    "request": "launch",
    "mainClass": "${file}",
    "args": "< \"${workspaceFolder}/src/main/resources/uva/${input:problemNumber}/1.in\"",
    "inputs": [
        {
            "id": "problemNumber",
            "type": "promptString",
            "description": "Enter UVa problem number (e.g. 100, 101, 10410)",
            "default": "100"
        }
    ]
}

Quick summary – what to use in 2025/2026

Method Reliability Windows macOS/Linux Recommended?
args: "< \"path\"" ★★★★★ Yes Yes Yes (most popular)
args: ["<", "path"] ★★★★☆ Yes Yes Yes (clean)
redirector: { "input": "..." } ★★☆☆☆ partial partial Avoid if possible
console": "externalTerminal" + manual < ★★★☆☆ Yes Yes Fallback

Most people today just use:

"args": "< \"${workspaceFolder}/src/main/resources/uva/${problem}/1.in\""

Good luck with UVa / competitive programming!

References:

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