Jython - Calling Python from Java

Let's say you do most of your development in Java, however, there is some existing Python code you need to reuse. In this post, I'll show you how to use Jython to call Python from Java.

Write a Java wrapper class:

public class JythonDemo {

    public int testMe(int num1, int num2) {
        PythonInterpreter python = new PythonInterpreter();

        python.set("num1", num1);
        python.set("num2", num2);
        python.exec("num3 = num1 + num2");
        PyObject num3 = python.get("num3");

        return Integer.parseInt(num3.toString());

    }
}

If using Maven, here is your pom.xml:

<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>
    <groupId>com.noushin</groupId>
    <artifactId>demo</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>war</packaging>
    <name>demo</name>
    <description>Demo</description>

    <dependencies>
        <dependency>
            <groupId>org.python</groupId>
            <artifactId>jython-standalone</artifactId>
            <version>2.5.2</version>
        </dependency>
    </dependencies>

</project>

Just call testMe(), and that'll run your Python code:

JythonDemo jythonDemo = new JythonDemo();
int result = jythonDemo.testMe();

Sending emails with attachments

In this example, I will show you how to use Java and Spring to send an email with attachments. Here is the main class to start things off:

package com.noushin.spring.email;

import java.io.File;
import java.util.ArrayList;
import java.util.Collection;

import javax.mail.MessagingException;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

/**
 * Main class to demonstrate sending an email with attachments.
 * 
 * @author nbashir
 * 
 */
public class EmailMain {

   public static void main(String[] args) {
      ApplicationContext ctx = new ClassPathXmlApplicationContext("application-context.xml");
      try {
         if (ctx != null) {
            Emailer emailer = ctx.getBean(Emailer.class);
            Collection<File> attachments = new ArrayList<File>();
            File attachment = new File("/home/nbashir/file.txt");
            attachments.add(attachment);
            emailer.sendEmail("Test Email", "Please see attached file(s).", attachments);
         }
      }
      catch (MessagingException me) {
         // TODO Auto-generated catch block
         me.printStackTrace();
      }
      catch (Exception ex) {
         ex.printStackTrace();
      }
   }
}

And Emailer class that generates an Email message, attaches files to it, and delivers.

package com.noushin.spring.email;

import java.io.File;
import java.util.Collection;

import javax.mail.MessagingException;
import javax.mail.internet.MimeMessage;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.core.io.FileSystemResource;
import org.springframework.mail.javamail.JavaMailSender;
import org.springframework.mail.javamail.MimeMessageHelper;
import org.springframework.stereotype.Component;

@Component
public class Emailer {

   @Autowired
   @Qualifier("mailSender")
   private JavaMailSender mailSender;

   @Value("${email.recipients}")
   private String emailRecipients;
   @Value("${email.from}")
   private String emailFrom;
   @Value("${email.reply.to}")
   private String emailReplyTo;

   /**
    * Send an email with attachments
    * 
    * @param subject email's subject line
    * @param body email's body
    * @param attachments list of attachments
    * 
    * @throws MessagingException 
    */
   public void sendEmail(String subject, String body, Collection<File> attachments) throws MessagingException {

      MimeMessage message = mailSender.createMimeMessage();
      MimeMessageHelper msgHelper = new MimeMessageHelper(message, MimeMessageHelper.MULTIPART_MODE_MIXED_RELATED);

      String[] recipients = getRecipients(emailRecipients);
      if (recipients != null) {
         for (int i = 0; i < recipients.length; i++)
            msgHelper.addTo(recipients[i]);
      }
      msgHelper.setFrom(emailFrom);
      msgHelper.setReplyTo(emailReplyTo);
      msgHelper.setSubject(subject);
      msgHelper.setText(body, true);

      if (attachments != null) {
         String filename = null;
         for (File attachment : attachments) {
            filename = attachment.getName();
            FileSystemResource res = new FileSystemResource(attachment);
            msgHelper.addAttachment(filename, res);
         }
      }

      mailSender.send(message);
   }

   /**
    * Return a list of strings
    * 
    * @param csvList a string containing a comma separated values 
    * @return a list of strings
    */
   public String[] getRecipients(String csvList) {
      String[] values = null;
      if (csvList != null) {
         values = csvList.split(",");
         for (int i = 0; i < values.length; i++)
            values[i] = values[i].trim();
      }
      return values;
   }
}

The pom file you need:

<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>

    <groupId>com.noushin.spring</groupId>
    <artifactId>email</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>
    <name>email</name>
    <url>http://maven.apache.org</url>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <spring.version>4.0.3.RELEASE</spring.version>
        <java.mail>1.4.7</java.mail>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-context</artifactId>
            <version>${spring.version}</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-context-support</artifactId>
            <version>${spring.version}</version>
        </dependency>

        <dependency>
            <groupId>javax.mail</groupId>
            <artifactId>mail</artifactId>
            <version>${java.mail}</version>
        </dependency>

    </dependencies>

</project>

And application context:

<?xml version="1.0" encoding="UTF-8"?>
<beans 
    xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
    xmlns:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="
        http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd">

    <context:property-placeholder location="file:/home/nbashir/email.properties" />
    
    <!-- Activate annotation configured components -->
    <context:annotation-config />

    <!-- Scan components for annotations within the configured package -->
    <context:component-scan base-package="com.noushin.spring.email" />
        
    <!-- Email handler -->
    <bean id="mailSender" class="org.springframework.mail.javamail.JavaMailSenderImpl">
        <property name="host" value="${email.host}" />
        <property name="port" value="${email.port}" />
    </bean>

</beans>