Five postures for spring boot to send e-mail: (personally test OK, list some stepped pits for brothers, and hold it if you think it's helpful!)

Email sending is actually a very common requirement, which can be used in user registration, password retrieval and other places. The steps of sending email using JavaSE code are still very cumbersome. Spring Boot provides relevant automatic configuration classes for email sending, which makes email sending very easy. In this article, we'll find out! Take a look at the 5 poses for sending mail using Spring Boot.

Mail Foundation

We often hear all kinds of mail protocols, such as SMTP, POP3 and IMAP. What are the functions and differences of these protocols? Let's discuss this problem first.

SMTP is an application layer protocol based on TCP/IP. Its status is a bit similar to HTTP. The default listening port number of SMTP server is 25. Seeing this, my friends may think that since SMTP protocol is an application layer protocol based on TCP/IP, can I also send an email through Socket? The answer is yes.

In life, we have to go through the following steps to deliver an email:

Xiao Wang from Shenzhen first delivered the mail to the post office in Shenzhen
The post office in Shenzhen delivers mail to the post office in Shanghai
Xiao Zhang from Shanghai came to the post office to pick up the mail

This is a reduced version of the email sending process in life. These three steps can correspond to our mail sending process respectively, assuming that aaa@qq.com Send mail to 111@163.com :

aaa@qq.com First deliver the mail to Tencent's mail server
Tencent's mail server delivers our mail to Netease's mail server
111@163.com Log in to Netease's mail server to view mail

Mail delivery is roughly this process, which involves multiple protocols. Let's take a look at them respectively.

The full name of SMTP protocol is Simple Mail Transfer Protocol, which is translated into Simple Mail Transfer Protocol. It defines the communication rules between mail client software and SMTP server, and between SMTP server and SMTP server.

in other words aaa@qq.com Users first deliver mail to Tencent's SMTP server, which uses the SMTP protocol. Then Tencent's SMTP server delivers mail to Netease's SMTP server, which still uses the SMTP protocol. The SMTP server is used to receive mail.

The full name of POP3 protocol is Post Office Protocol, which is translated into Post Office Protocol. It defines the communication rules between mail client and POP3 server. Under what scenario will this protocol be used? When the mail arrives at Netease's SMTP server, 111@163.com Users need to log in to the server to view the mail. This protocol is used at this time: the mail service provider will provide special mail storage space for each user. After receiving the mail, the SMTP server will save the mail to the mail storage space of the corresponding user. If users want to read the mail, they need to complete it through the POP3 mail server of the mail service provider.

Finally, some friends may have heard of IMAP protocol, which is an extension of POP3 protocol with stronger functions and similar functions. I won't repeat it here.

preparation

At present, most domestic email service providers are not allowed to directly use the user name / password to send email in the code. They all need to apply for the authorization code first. Here, take QQ email as an example to demonstrate the application process of the authorization code: first, we need to log in to the QQ email web page and click the setting button above:

p266

Then click the Account tab:

p267

Find the option to enable POP3/SMTP in the Account tab, as follows:

p268

Click open to open the relevant functions. The opening process requires mobile phone number verification. You can operate according to the steps without repeating. After successful opening, you can obtain an authorization code and save the number for later use.

Project creation

Next, we can create the project. In Spring Boot, an automatic configuration class is provided for mail sending. Developers only need to add relevant dependencies and configure the basic information of the mailbox to send mail.

First, create a Spring Boot project and introduce mail sending dependency:

After creation, the project dependencies are as follows:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-mail</artifactId>
</dependency>
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
</dependency>

Configure basic mailbox information

After the project is successfully created, the next step is in application Basic information of configuring mailbox in properties:

spring.mail.host=smtp.qq.com
spring.mail.port=587
spring.mail.username=1510161612@qq.com
spring.mail.password=ubknfzhjkhrbbabe
spring.mail.default-encoding=UTF-8
spring.mail.properties.mail.smtp.socketFactoryClass=javax.net.ssl.SSLSocketFactory
spring.mail.properties.mail.debug=true

The meanings of configuration are as follows:

Configure the SMTP server address. Note: I stepped on the pit and didn't look carefully. At that time, it took a long time to find it (email type qq: smtp.qq.com/163: smtp.163.com)
Port of SMTP server (email type qq: 587/163: 25)
Configure mailbox user name
Configure the password. Note that it is not the real password, but the authorization code just applied for
Default message code
Accessories SSL encryption factory
Indicates that the DEBUG mode is enabled. In this way, the log of mail sending process will be printed on the console to facilitate troubleshooting

If you don't know the port or address of the smtp server, you can refer to the email document of Tencent

https://service.mail.qq.com/cgi-bin/help?subtype=1&&id=28&&no=371

After that, Spring Boot will automatically help us configure the mail sending class. The relevant configuration is at www springframework. boot. autoconfigure. mail. In the mailsenderautoconfiguration class, part of the source code is as follows:

@Configuration
@ConditionalOnClass({ MimeMessage.class, MimeType.class, MailSender.class })
@ConditionalOnMissingBean(MailSender.class)
@Conditional(MailSenderCondition.class)
@EnableConfigurationProperties(MailProperties.class)
@Import({ MailSenderJndiConfiguration.class, MailSenderPropertiesConfiguration.class })
publicclass MailSenderAutoConfiguration {
}

From this code, you can see that another configuration class MailSenderPropertiesConfiguration is imported, which provides tool classes related to mail sending:

@Configuration
@ConditionalOnProperty(prefix = "spring.mail", name = "host")
class MailSenderPropertiesConfiguration {
        privatefinal MailProperties properties;
        MailSenderPropertiesConfiguration(MailProperties properties) {
                this.properties = properties;
        }
        @Bean
        @ConditionalOnMissingBean
        public JavaMailSenderImpl mailSender() {
                JavaMailSenderImpl sender = new JavaMailSenderImpl();
                applyProperties(sender);
                return sender;
        }
}

As you can see, an instance of JavaMailSenderImpl is created here. JavaMailSenderImpl is an implementation of JavaMailSender. We will use JavaMailSenderImpl to complete mail sending.

After the above two steps are completed, the preparation for e-mail sending is completed, and then you can send e-mail directly.

There are five different ways to send, let's look at them one by one.

Send simple mail

Simple mail means that the mail content is an ordinary text document:

@Autowired
JavaMailSender javaMailSender;
@Test
public void sendSimpleMail() {
    SimpleMailMessage message = new SimpleMailMessage();
    message.setSubject("This is a test email");
    message.setFrom("1510161612@qq.com");
    message.setTo("25xxxxx755@qq.com");
    message.setCc("37xxxxx37@qq.com");
    message.setBcc("14xxxxx098@qq.com");
    message.setSentDate(new Date());
    message.setText("This is the body of the test message");
    javaMailSender.send(message);
}

From top to bottom, the code meanings are as follows:

Build a mail object
Set message subject
Set mail sender
Set mail recipients. You can have multiple recipients
Set email CC person, and there can be multiple CC persons
Set a secret CC person, which can have multiple
Set mail sending date
Set the body of the message
Send mail

Finally, by executing this method, the mail can be sent. The sending effect diagram is as follows:

Send mail with attachments

Email attachments can be pictures or ordinary files, which are supported.

@Test
public void sendAttachFileMail() throws MessagingException {
    MimeMessage mimeMessage = javaMailSender.createMimeMessage();
    MimeMessageHelper helper = new MimeMessageHelper(mimeMessage,true);
    helper.setSubject("This is a test email");
    helper.setFrom("1510161612@qq.com");
    helper.setTo("25xxxxx755@qq.com");
    helper.setCc("37xxxxx37@qq.com");
    helper.setBcc("14xxxxx098@qq.com");
    helper.setSentDate(new Date());
    helper.setText("This is the body of the test message");
    helper.addAttachment("javaboy.jpg",new File("C:\\Users\\sang\\Downloads\\javaboy.png"));
    javaMailSender.send(mimeMessage);
}

Note that there are some differences between the construction of mail objects here and the previous text. Here is to obtain a complex mail object through javaMailSender, and then use MimeMessageHelper to configure the mail. MimeMessageHelper is an auxiliary tool class for mail configuration. When it is created, true means to build a multipart message type mail, After we have MimeMessageHelper, our mail configuration is done by MimeMessageHelper.

Finally, add an attachment through the addAttachment method.

Execute this method, and the email sending effect is as follows:

Send mail with picture resources

What is the difference between picture resources and attachments? Picture resources are placed in the body of the email, that is, as soon as you open the email, you can see the picture. However, generally speaking, this method is not recommended. Some companies will limit the size of email content (because this method sends pictures together).

@Test
public void sendImgResMail() throws MessagingException {
    MimeMessage mimeMessage = javaMailSender.createMimeMessage();
    MimeMessageHelper helper = new MimeMessageHelper(mimeMessage, true);
    helper.setSubject("This is a test email");
    helper.setFrom("1510161612@qq.com");
    helper.setTo("25xxxxx755@qq.com");
    helper.setCc("37xxxxx37@qq.com");
    helper.setBcc("14xxxxx098@qq.com");
    helper.setSentDate(new Date());
    helper.setText("<p>hello Hello everyone, this is a test email. This email contains two kinds of pictures, as follows:</p><p>First picture:</p><img src='cid:p01'/><p>Second picture:</p><img src='cid:p02'/>",true);
    helper.addInline("p01",new FileSystemResource(new File("C:\\Users\\sang\\Downloads\\javaboy.png")));
    helper.addInline("p02",new FileSystemResource(new File("C:\\Users\\sang\\Downloads\\javaboy2.png")));
    javaMailSender.send(mimeMessage);
}

The email text here is an HTML text. The image resources involved in it are first occupied by a placeholder. The second parameter true of the setText method means that the first parameter is an HTML text.

After setText, add image resources through the addInline method.

Finally, execute this method and send mail. The effect is as follows:

In the actual development of the company, neither the first nor the third is the most used email sending scheme. Because normally, the contents of e-mails are relatively rich, most e-mails are presented through HTML. If you directly splice HTML strings, it is difficult to maintain in the future. In order to solve this problem, generally, there will be corresponding e-mail templates when sending e-mails. The two most representative templates are Freemarker template and Thyemeleaf template.

Using Freemarker as mail template

First of all, we need to introduce Freemarker dependency:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-freemarker</artifactId>
</dependency>

Then create a "mail" in the "resources/templates" directory FTL # as email sending template:

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<p>hello Welcome to join xxx Big family, your entry information is as follows:</p>
<table border="1">
    <tr>
        <td>full name</td>
        <td>${username}</td>
    </tr>
    <tr>
        <td>Job number</td>
        <td>${num}</td>
    </tr>
    <tr>
        <td>salary</td>
        <td>${salary}</td>
    </tr>
</table>
<div style="color: #Ff1a0e "> work together to create brilliance < / div >
</body>
</html>

Next, render the mail template into HTML and send it.

@Test
public void sendFreemarkerMail() throws MessagingException, IOException, TemplateException {
    MimeMessage mimeMessage = javaMailSender.createMimeMessage();
    MimeMessageHelper helper = new MimeMessageHelper(mimeMessage, true);
    helper.setSubject("This is a test email");
    helper.setFrom("1510161612@qq.com");
    helper.setTo("25xxxxx755@qq.com");
    helper.setCc("37xxxxx37@qq.com");
    helper.setBcc("14xxxxx098@qq.com");
    helper.setSentDate(new Date());
    //Build the basic configuration of Freemarker
    Configuration configuration = new Configuration(Configuration.VERSION_2_3_0);
    // Configure template location
    ClassLoader loader = MailApplication.class.getClassLoader();
    configuration.setClassLoaderForTemplateLoading(loader, "templates");
    //Load template
    Template template = configuration.getTemplate("mail.ftl");
    User user = new User();
    user.setUsername("javaboy");
    user.setNum(1);
    user.setSalary((double) 99999);
    StringWriter out = new StringWriter();
    //Template rendering, the rendered result will be saved in out, and the html string in out can be sent
    template.process(user, out);
    helper.setText(out.toString(),true);
    javaMailSender.send(mimeMessage);
}

It should be noted that although the automatic configuration of "Freemarker" is introduced, we directly use "new Configuration" to reconfigure "Freemarker", so the default configuration of Freemarker does not take effect here. Therefore, when filling in the template location, the value is "templates".

Call this method to send mail. The effect diagram is as follows:

Use Thymeleaf as mail template

It is recommended to use Thymeleaf in Spring Boot to build mail templates. Because the automatic configuration of Thymeleaf provides a TemplateEngine, through which the Thymeleaf template can be easily rendered into HTML. At the same time, the automatic configuration of Thymeleaf continues to be effective here.

First, introduce Thymeleaf dependency:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-thymeleaf</artifactId>
</dependency>

Then, create a # Thymeleaf # mail template:

<!DOCTYPE html>
<html lang="en" xmlns:th="http://www.thymeleaf.org">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<p>hello Welcome to join xxx Big family, your entry information is as follows:</p>
<table border="1">
    <tr>
        <td>full name</td>
        <td th:text="${username}"></td>
    </tr>
    <tr>
        <td>Job number</td>
        <td th:text="${num}"></td>
    </tr>
    <tr>
        <td>salary</td>
        <td th:text="${salary}"></td>
    </tr>
</table>
<div style="color: #Ff1a0e "> work together to create brilliance < / div >
</body>
</html>

Next, send an email:

@Autowired
TemplateEngine templateEngine;

@Test
public void sendThymeleafMail() throws MessagingException {
    MimeMessage mimeMessage = javaMailSender.createMimeMessage();
    MimeMessageHelper helper = new MimeMessageHelper(mimeMessage, true);
    helper.setSubject("This is a test email");
    helper.setFrom("1510161612@qq.com");
    helper.setTo("25xxxxx755@qq.com");
    helper.setCc("37xxxxx37@qq.com");
    helper.setBcc("14xxxxx098@qq.com");
    helper.setSentDate(new Date());
    Context context = new Context();
    context.setVariable("username", "javaboy");
    context.setVariable("num","000001");
    context.setVariable("salary", "99999");
    String process = templateEngine.process("mail.html", context);
    helper.setText(process,true);
    javaMailSender.send(mimeMessage);
}

Call this method to send mail. The effect diagram is as follows:

Well, these are the five email sending postures we talked about today. I wonder if you have mastered them?

Keywords: Java Spring Boot

Added by Jona on Tue, 01 Feb 2022 01:32:49 +0200

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