BAEL-3925 - How to call Python from Java

java-python-interop/README.md

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+## Java Python Interop
+
+This module contains articles about Java and Python interoperability.  
+
+### Relevant Articles:

java-python-interop/pom.xml

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+<?xml version="1.0" encoding="UTF-8" ?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <artifactId>java-python-interop</artifactId>
+    <version>0.0.1-SNAPSHOT</version>
+    <name>java-python-interop</name>
+
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-modules</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.python</groupId>
+            <artifactId>jython-slim</artifactId>
+            <version>${jython.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-exec</artifactId>
+            <version>${commons-exec.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>${assertj.version}</version>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <finalName>java-python-interop</finalName>
+        <resources>
+            <resource>
+                <directory>src/main/resources</directory>
+                <filtering>true</filtering>
+            </resource>
+            <resource>
+                <directory>src/test/resources</directory>
+                <filtering>true</filtering>
+            </resource>
+        </resources>
+    </build>
+
+    <properties>
+        <jython.version>2.7.2</jython.version>
+        <commons-exec.version>1.3</commons-exec.version>
+        <assertj.version>3.6.1</assertj.version>
+    </properties>
+
+</project>

java-python-interop/src/main/java/com/baeldung/python/interop/ScriptEngineManagerUtils.java

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+package com.baeldung.python.interop;
+
+import java.util.List;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import javax.script.ScriptEngineFactory;
+import javax.script.ScriptEngineManager;
+
+public class ScriptEngineManagerUtils {
+
+    private static final Logger LOGGER = LoggerFactory.getLogger(ScriptEngineManagerUtils.class);
+
+    private ScriptEngineManagerUtils() {
+    }
+
+    public static void listEngines() {
+        ScriptEngineManager manager = new ScriptEngineManager();
+        List<ScriptEngineFactory> engines = manager.getEngineFactories();
+
+        for (ScriptEngineFactory engine : engines) {
+            LOGGER.info("Engine name: {}", engine.getEngineName());
+            LOGGER.info("Version: {}", engine.getEngineVersion());
+            LOGGER.info("Language: {}", engine.getLanguageName());
+
+            LOGGER.info("Short Names:");
+            for (String names : engine.getNames()) {
+                LOGGER.info(names);
+            }
+        }
+    }
+
+}

java-python-interop/src/main/resources/logback.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<configuration>
+    <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
+        <encoder>
+            <pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n
+            </pattern>
+        </encoder>
+    </appender>
+
+    <root level="INFO">
+        <appender-ref ref="STDOUT" />
+    </root>
+</configuration>

java-python-interop/src/test/java/com/baeldung/python/interop/JavaPythonInteropUnitTest.java

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+package com.baeldung.python.interop;
+
+import static org.hamcrest.Matchers.containsString;
+import static org.hamcrest.Matchers.empty;
+import static org.hamcrest.Matchers.hasItem;
+import static org.hamcrest.Matchers.is;
+import static org.hamcrest.Matchers.not;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertThat;
+
+import java.io.BufferedReader;
+import java.io.ByteArrayOutputStream;
+import java.io.File;
+import java.io.FileReader;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.InputStreamReader;
+import java.io.StringWriter;
+import java.util.List;
+import java.util.stream.Collectors;
+
+import javax.script.ScriptContext;
+import javax.script.ScriptEngine;
+import javax.script.ScriptEngineManager;
+import javax.script.SimpleScriptContext;
+
+import org.apache.commons.exec.CommandLine;
+import org.apache.commons.exec.DefaultExecutor;
+import org.apache.commons.exec.ExecuteException;
+import org.apache.commons.exec.PumpStreamHandler;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.ExpectedException;
+import org.python.core.PyException;
+import org.python.core.PyObject;
+import org.python.util.PythonInterpreter;
+
+public class JavaPythonInteropUnitTest {
+
+    @Rule
+    public ExpectedException thrown = ExpectedException.none();
+
+    @Test
+    public void givenPythonScript_whenPythonProcessInvoked_thenSuccess() throws Exception {
+        ProcessBuilder processBuilder = new ProcessBuilder("python", resolvePythonScriptPath("hello.py"));
+        processBuilder.redirectErrorStream(true);
+
+        Process process = processBuilder.start();
+        List<String> results = readProcessOutput(process.getInputStream());
+
+        assertThat("Results should not be empty", results, is(not(empty())));
+        assertThat("Results should contain output of script: ", results, hasItem(containsString("Hello Baeldung Readers!!")));
+
+        int exitCode = process.waitFor();
+        assertEquals("No errors should be detected", 0, exitCode);
+    }
+
+    @Test
+    public void givenPythonScriptEngineIsAvailable_whenScriptInvoked_thenOutputDisplayed() throws Exception {
+        StringWriter output = new StringWriter();
+        ScriptContext context = new SimpleScriptContext();
+        context.setWriter(output);
+
+        ScriptEngineManager manager = new ScriptEngineManager();
+        ScriptEngine engine = manager.getEngineByName("python");
+        engine.eval(new FileReader(resolvePythonScriptPath("hello.py")), context);
+        assertEquals("Should contain script output: ", "Hello Baeldung Readers!!", output.toString()
+            .trim());
+    }
+
+    @Test
+    public void givenPythonInterpreter_whenPrintExecuted_thenOutputDisplayed() {
+        try (PythonInterpreter pyInterp = new PythonInterpreter()) {
+            StringWriter output = new StringWriter();
+            pyInterp.setOut(output);
+
+            pyInterp.exec("print('Hello Baeldung Readers!!')");
+            assertEquals("Should contain script output: ", "Hello Baeldung Readers!!", output.toString()
+                .trim());
+        }
+    }
+
+    @Test
+    public void givenPythonInterpreter_whenNumbersAdded_thenOutputDisplayed() {
+        try (PythonInterpreter pyInterp = new PythonInterpreter()) {
+            pyInterp.exec("x = 10+10");
+            PyObject x = pyInterp.get("x");
+            assertEquals("x: ", 20, x.asInt());
+        }
+    }
+
+    @Test
+    public void givenPythonInterpreter_whenErrorOccurs_thenExceptionIsThrown() {
+        thrown.expect(PyException.class);
+        thrown.expectMessage("ImportError: No module named syds");
+
+        try (PythonInterpreter pyInterp = new PythonInterpreter()) {
+            pyInterp.exec("import syds");
+        }
+    }
+
+    @Test
+    public void givenPythonScript_whenPythonProcessExecuted_thenSuccess() throws ExecuteException, IOException {
+        String line = "python " + resolvePythonScriptPath("hello.py");
+        CommandLine cmdLine = CommandLine.parse(line);
+
+        ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
+        PumpStreamHandler streamHandler = new PumpStreamHandler(outputStream);
+
+        DefaultExecutor executor = new DefaultExecutor();
+        executor.setStreamHandler(streamHandler);
+
+        int exitCode = executor.execute(cmdLine);
+        assertEquals("No errors should be detected", 0, exitCode);
+        assertEquals("Should contain script output: ", "Hello Baeldung Readers!!", outputStream.toString()
+            .trim());
+    }
+
+    private List<String> readProcessOutput(InputStream inputStream) throws IOException {
+        try (BufferedReader output = new BufferedReader(new InputStreamReader(inputStream))) {
+            return output.lines()
+                .collect(Collectors.toList());
+        }
+    }
+
+    private String resolvePythonScriptPath(String filename) {
+        File file = new File("src/test/resources/" + filename);
+        return file.getAbsolutePath();
+    }
+
+}

java-python-interop/src/test/resources/hello.py

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+print("Hello Baeldung Readers!!")

pom.xml

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                 <module>java-lite</module>
                 <module>java-numbers</module>
                 <module>java-numbers-2</module>
-                <module>java-numbers-3</module>
+		<module>java-numbers-3</module>
+		<module>java-python-interop</module>
                 <module>java-rmi</module>
                 <module>java-spi</module>
                 <module>java-vavr-stream</module>