Add Java as a supported output language

CHANGELOG.md

@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 - **Go output language**: `output_language: "go"` is now supported alongside python/javascript/typescript, generating a standard-library-first (`net/http`, `encoding/json`) Go program, with the same auth-hardcoding/refresh and bot-detection-fallback guidance as the other languages.
+- **Java output language**: `output_language: "java"` is now supported alongside python/javascript/typescript, generating a small Maven project using `java.net.http.HttpClient` (JDK 11+, no HTTP library dependency) and Gson for JSON, with the same auth-hardcoding/refresh guidance as the other languages.
 
 ## [0.10.0] - 2026-06-01
 

README.md

@@ -96,7 +96,7 @@ Settings live in `~/.reverse-api/config.json` and can be edited via `/settings`
 
 - **Models**: Sonnet 4.6 (default), Opus 4.6 (most capable), Haiku 4.5 (fastest). For OpenCode see [models.dev](https://models.dev).
 - **SDK**: `claude` (default), `opencode`, `cursor`, or `copilot` (GitHub Copilot).
-- **Output language**: `python`, `javascript`, `typescript`, or `go`.
+- **Output language**: `python`, `javascript`, `typescript`, `go`, or `java`.
 
 ## CLI
 

src/reverse_api/base_engineer.py

@@ -2,6 +2,7 @@
 
 import asyncio
 import os
+import shlex
 from abc import ABC, abstractmethod
 from pathlib import Path
 from typing import Any
@@ -34,6 +35,7 @@ class BaseEngineer(ABC):
         "javascript": ".js",
         "typescript": ".ts",
         "go": ".go",
+        "java": ".java",
     }
 
     def __init__(
@@ -441,6 +443,7 @@ def _get_language_name(self) -> str:
             "javascript": "JavaScript",
             "typescript": "TypeScript",
             "go": "Go",
+            "java": "Java",
         }.get(self.output_language, "Python")
 
     def _get_existing_client_guidance(self) -> str:
@@ -465,6 +468,27 @@ def _get_client_filename(self) -> str:
 
     def _get_run_command(self) -> str:
         """Return the command to run the generated client."""
+        if self.output_language == "java":
+            # Unlike python/node/npx (which happily take a plain relative
+            # filename regardless of the agent's actual cwd, scripts_dir.
+            # parent.parent — see analyze_and_generate's ClaudeAgentOptions),
+            # Maven hard-fails immediately if invoked from a directory with
+            # no pom.xml, no upward search. -f points it straight at the
+            # right project file regardless of cwd, rather than relying on
+            # the agent to cd there itself first. shlex.quote(), not manual
+            # double-quoting — output_dir (and so scripts_dir) isn't
+            # guaranteed free of shell metacharacters, and naive f'"{path}"'
+            # still lets $()/backticks expand inside double quotes.
+            # .resolve(): a relative --output-dir would otherwise be
+            # re-interpreted against the agent's cwd (scripts_dir.parent.
+            # parent) instead of the original cwd it was relative to,
+            # pointing -f at the wrong, doubly-nested location.
+            # exec:exec (spawn a real java process), not exec:java —
+            # exec:java invokes main() reflectively in-process, which fails
+            # on the package-private ApiClient class the Java partial
+            # requires ("symbolic reference class is not accessible").
+            pom = shlex.quote(str(self.scripts_dir.resolve() / "pom.xml"))
+            return f"mvn -q -f {pom} compile exec:exec"
         return {
             "python": "python api_client.py",
             "javascript": "node api_client.js",
@@ -584,6 +608,8 @@ def _get_auto_output_files(self, language_name: str, client_filename: str) -> st
                 f"\n3. `{self.scripts_dir}/go.mod` and `{self.scripts_dir}/go.sum` - "
                 "Only if external dependencies are needed"
             )
+        elif self.output_language == "java":
+            return base + f"\n3. `{self.scripts_dir}/pom.xml` - Maven project file (Gson dependency, exec-maven-plugin)"
         return base
 
     @abstractmethod

src/reverse_api/cli.py

@@ -1084,6 +1084,7 @@ def handle_settings(mode_color=THEME_PRIMARY):
             Choice(title="javascript", value="javascript"),
             Choice(title="typescript", value="typescript"),
             Choice(title="go", value="go"),
+            Choice(title="java", value="java"),
             Choice(title="back", value="back"),
         ]
         lang = questionary.select(

src/reverse_api/config.py

@@ -20,7 +20,7 @@
     "opencode_model": "claude-opus-4-6",
     "opencode_provider": "anthropic",
     "output_dir": None,  # None means use ~/.reverse-api/runs
-    "output_language": "python",  # "python", "javascript", "typescript", or "go"
+    "output_language": "python",  # "python", "javascript", "typescript", "go", or "java"
     "real_time_sync": True,  # Enable real-time file sync during engineering
     "sdk": "claude",  # "claude", "opencode", "copilot", or "cursor"
 }

src/reverse_api/engineer.py

@@ -232,7 +232,7 @@ def run_reverse_engineering(
         cursor_setting_sources: Optional explicit list (overrides cursor_web_search), e.g. ["project","user","all"].
         enable_sync: Enable real-time file syncing during engineering
         is_fresh: Whether to start fresh (ignore previous scripts)
-        output_language: Target language - "python", "javascript", "typescript", or "go"
+        output_language: Target language - "python", "javascript", "typescript", "go", or "java"
         output_mode: Output mode - "client" for API client code, "docs" for OpenAPI specification
     """
     if sdk == "opencode":

src/reverse_api/prompts/__init__.py

@@ -54,7 +54,7 @@ def load_language_partial(language: str, **kwargs: str) -> str:
     """Load the language-specific codegen instructions partial.
 
     Args:
-        language: One of "python", "javascript", "typescript", "go".
+        language: One of "python", "javascript", "typescript", "go", "java".
         **kwargs: Placeholder values (scripts_dir, client_filename, run_command).
     """
     return load(f"partials/_language_{language}", **kwargs)

src/reverse_api/prompts/partials/_language_java.md

@@ -0,0 +1,41 @@
+**Generate a Java program** that replicates the API calls found in the traffic. The following are guidelines — use your judgment on what's appropriate for the specific API:
+
+- Use `java.net.http.HttpClient` (built into the JDK since 11) for requests — no HTTP library dependency needed
+- Use Gson for JSON parsing/serialization — the one dependency this needs, since the JDK has no built-in JSON support
+- Create a minimal Maven project (`pom.xml`) with the Gson dependency and the `exec-maven-plugin`, so the client runs with a single command and no extra flags. A conventional Maven layout only compiles `src/main/java`, but `{client_filename}` is saved at the project root (see below) — override the build's `<sourceDirectory>` to `.` (project root) in the POM so `mvn compile` actually finds and compiles it
+- Configure `exec-maven-plugin` for the `exec:exec` goal with exactly this configuration — do not use the `exec:java` goal or `<mainClass>`: `exec:java` invokes `main` reflectively in-process, which fails on the package-private `ApiClient` class described below ("symbolic reference class is not accessible"), while `exec:exec` spawns a real `java` process, and its `<classpath/>` element expands to the full dependency classpath with the correct platform-specific separator (`:` on macOS/Linux, `;` on Windows):
+
+  ```xml
+  <plugin>
+      <groupId>org.codehaus.mojo</groupId>
+      <artifactId>exec-maven-plugin</artifactId>
+      <version>3.1.0</version>
+      <configuration>
+          <executable>java</executable>
+          <arguments>
+              <argument>-classpath</argument>
+              <classpath/>
+              <argument>ApiClient</argument>
+          </arguments>
+      </configuration>
+  </plugin>
+  ```
+- Create a separate method for each distinct API endpoint, with a small class for its response shape
+- Reuse one `HttpClient` instance across requests rather than creating a new one per call
+- Include a `main` method with example usage
+- The output file is named `{client_filename}` (lowercase with underscores), so name the top-level class holding `main` exactly `ApiClient`, declared package-private, *without* the `public` modifier — a `public` class's filename must exactly match its class name, and this generator's file naming convention doesn't follow Java's usual PascalCase file naming. A package-private top-level class compiles and runs identically; it just isn't visible from other packages, which this single-file client has no need for.
+
+**Authentication & credentials:**
+- Hardcode all cookies, tokens, session IDs, and auth headers found in the traffic directly in the program
+- The user should be able to run the program immediately after `mvn compile` — no env vars, no additional config files, no manual setup beyond what's generated
+- If the API uses cookies, build the `HttpClient` with a `CookieHandler`/`CookieManager` so cookies persist across requests
+- If the API uses Bearer tokens or API keys, hardcode them in the request headers
+- Handle auth refresh so the program doesn't go stale: if you see a token refresh endpoint, OAuth refresh flow, or login endpoint in the traffic, implement automatic re-authentication when a request returns 401/403. If cookies have expiry, re-fetch them before they expire
+
+**Testing:**
+- Run: `{run_command}`
+- You have up to 5 attempts to fix issues
+
+Save the program to: `{scripts_dir}/{client_filename}`
+Save documentation to: `{scripts_dir}/README.md`
+Save the Maven project file to: `{scripts_dir}/pom.xml`

tests/test_base_engineer.py

@@ -1,5 +1,6 @@
 """Tests for base_engineer.py - BaseEngineer abstract class."""
 
+import shlex
 from pathlib import Path
 from typing import Any
 from unittest.mock import MagicMock, patch
@@ -197,6 +198,10 @@ def test_get_output_extension_go(self, tmp_path):
         """Go extension."""
         eng = self._make_engineer(tmp_path, output_language="go")
         assert eng._get_output_extension() == ".go"
+    def test_get_output_extension_java(self, tmp_path):
+        """Java extension."""
+        eng = self._make_engineer(tmp_path, output_language="java")
+        assert eng._get_output_extension() == ".java"
 
     def test_get_output_extension_unknown(self, tmp_path):
         """Unknown language defaults to .py."""
@@ -232,6 +237,38 @@ def test_get_run_command_go(self, tmp_path):
         """Run command for Go."""
         eng = self._make_engineer(tmp_path, output_language="go")
         assert eng._get_run_command() == "go run api_client.go"
+    def test_get_run_command_java(self, tmp_path):
+        """Run command for Java points -f at this run's own (resolved,
+        shell-quoted) pom.xml, not a bare relative path — the agent's cwd is
+        scripts_dir.parent.parent (see analyze_and_generate), and unlike
+        python/node/npx, Maven hard-fails with no upward search if invoked
+        from a directory with no pom.xml."""
+        eng = self._make_engineer(tmp_path, output_language="java")
+        expected_pom = shlex.quote(str(eng.scripts_dir.resolve() / "pom.xml"))
+        assert eng._get_run_command() == f"mvn -q -f {expected_pom} compile exec:exec"
+
+    def test_get_run_command_java_quotes_metacharacters(self, tmp_path):
+        """A scripts_dir containing shell metacharacters must round-trip
+        back to the literal path, not be left open to $()/backtick
+        expansion — what the naive f'"{path}"' approach got wrong."""
+        eng = self._make_engineer(tmp_path, output_language="java")
+        eng.scripts_dir = Path("/tmp/weird$(rm -rf ~) dir")
+        tokens = shlex.split(eng._get_run_command())
+        assert tokens[:2] == ["mvn", "-q"]
+        assert tokens[3] == str(eng.scripts_dir.resolve() / "pom.xml")
+
+    def test_get_run_command_java_resolves_relative_output_dir(self, tmp_path):
+        """A relative scripts_dir must be resolved to an absolute path before
+        being embedded in the command — otherwise, once the agent's cwd
+        moves to scripts_dir.parent.parent, the same relative string gets
+        re-interpreted from there and points at the wrong, doubly-nested
+        location."""
+        eng = self._make_engineer(tmp_path, output_language="java")
+        eng.scripts_dir = Path("relative_output/scripts/run123")
+        tokens = shlex.split(eng._get_run_command())
+        pom_arg = tokens[3]
+        assert Path(pom_arg).is_absolute()
+        assert pom_arg == str(eng.scripts_dir.resolve() / "pom.xml")
 
     def test_get_run_command_unknown(self, tmp_path):
         """Unknown language defaults to Python command."""
@@ -285,6 +322,12 @@ def test_go_prompt(self, tmp_path):
         system_prompt, user_message = eng._build_prompts()
         assert "Go program" in system_prompt
         assert "net/http" in system_prompt
+    def test_java_prompt(self, tmp_path):
+        """Java prompt includes Java-specific instructions."""
+        eng = self._make_engineer(tmp_path, output_language="java")
+        system_prompt, user_message = eng._build_prompts()
+        assert "Java program" in system_prompt
+        assert "HttpClient" in system_prompt
 
     def test_docs_prompt(self, tmp_path):
         """Docs mode prompt includes OpenAPI instructions."""

tests/test_prompts.py

@@ -81,6 +81,16 @@ def test_go_partial(self):
         assert "Go program" in text
         assert "net/http" in text
         assert "/tmp/scripts/api_client.go" in text
+    def test_java_partial(self):
+        text = load_language_partial(
+            "java",
+            scripts_dir="/tmp/scripts",
+            client_filename="api_client.java",
+            run_command="mvn -q compile exec:exec",
+        )
+        assert "Java program" in text
+        assert "HttpClient" in text
+        assert "/tmp/scripts/api_client.java" in text
 
 
 class TestEngineerTemplates: