springboot 邮件发送太慢的问题定位及解决方案

最近有个小功能，需要发送邮件。

使用了spring-boot-starter-mail组件进行邮件操作，却发现速度特别慢，每次发送都要20秒左右。为了解决这个问题，针对源码进行了一些研究和优化

xml 复制代码

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

问题定位

通过分析，发现主要在以下两部分比较耗时

创建连接 :查看源码发现org.springframework.mail.javamail.JavaMailSenderImpl的doSend方法每次发送邮件都会创建新的连接。每次创建连接都要10秒左右

java 复制代码

protected void doSend(MimeMessage[] mimeMessages, @Nullable Object[] originalMessages) throws MailException {
		Map<Object, Exception> failedMessages = new LinkedHashMap<>();
		Transport transport = null;

		try {
			for (int i = 0; i < mimeMessages.length; i++) {
				// Check transport connection first...
				if (transport == null || !transport.isConnected()) {
					if (transport != null) {
						try {
							transport.close();
						}
						catch (Exception ex) {
							// Ignore - we're reconnecting anyway
						}
						transport = null;
					}
					try {
						transport = connectTransport();
					}
					catch (AuthenticationFailedException ex) {
						throw new MailAuthenticationException(ex);
					}
					...

生成消息ID: 这里耗时其实是没想到的，通过查看源码发现在生成消息ID的时候，代码中会尝试去DNS服务查找跟自身IP符合的域名，这个操作特别耗时

解决方案

定位到了问题，解决方案自然也就有了

缓存TCP连接或池化

针对第一个问题，最常见的方式就是将Transport对象池化。感兴趣的可以自己去实现，通过common-pool就可以轻松实现了，

由于我的功能更简单，单个资源就够用了，所有就做了下面这种直接缓存连接对象即可最简单的优化，代码如下

java 复制代码

package com.leewan.server.service.impl;

import jakarta.mail.Address;
import jakarta.mail.AuthenticationFailedException;
import jakarta.mail.Transport;
import jakarta.mail.internet.MimeMessage;
import org.springframework.mail.MailAuthenticationException;
import org.springframework.mail.MailException;
import org.springframework.mail.MailSendException;
import org.springframework.mail.javamail.JavaMailSenderImpl;

import java.util.Date;
import java.util.LinkedHashMap;
import java.util.Map;

public class MailSenderImpl extends JavaMailSenderImpl {

    private static final String HEADER_MESSAGE_ID = "Message-ID";

    private Transport transport;

    @Override
    protected synchronized void doSend(MimeMessage[] mimeMessages, Object[] originalMessages) throws MailException {
        Map<Object, Exception> failedMessages = new LinkedHashMap<>();

        for (int i = 0; i < mimeMessages.length; i++) {

            // Check transport connection first...
            if (transport == null || !transport.isConnected()) {
                try {
                    transport = connectTransport();
                }
                catch (AuthenticationFailedException ex) {
                    throw new MailAuthenticationException(ex);
                }
                catch (Exception ex) {
                    // Effectively, all remaining messages failed...
                    for (int j = i; j < mimeMessages.length; j++) {
                        Object original = (originalMessages != null ? originalMessages[j] : mimeMessages[j]);
                        failedMessages.put(original, ex);
                    }
                    throw new MailSendException("Mail server connection failed", ex, failedMessages);
                }
            }

            // Send message via current transport...
            MimeMessage mimeMessage = mimeMessages[i];
            try {
                if (mimeMessage.getSentDate() == null) {
                    mimeMessage.setSentDate(new Date());
                }
                String messageId = mimeMessage.getMessageID();


                mimeMessage.saveChanges();

                if (messageId != null) {
                    // Preserve explicitly specified message id...
                    mimeMessage.setHeader(HEADER_MESSAGE_ID, messageId);
                }
                Address[] addresses = mimeMessage.getAllRecipients();



                transport.sendMessage(mimeMessage, (addresses != null ? addresses : new Address[0]));
            }
            catch (Exception ex) {
                Object original = (originalMessages != null ? originalMessages[i] : mimeMessage);
                failedMessages.put(original, ex);
            }
        }

        if (!failedMessages.isEmpty()) {
            throw new MailSendException(failedMessages);
        }
    }
}

配置类如下

java 复制代码

package com.leewan.server.context.mail;

import com.leewan.server.service.impl.MailSenderImpl;
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
import org.springframework.boot.autoconfigure.mail.MailProperties;
import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.mail.javamail.JavaMailSender;
import org.springframework.mail.javamail.JavaMailSenderImpl;

import java.util.Map;
import java.util.Properties;

@Configuration
@EnableConfigurationProperties(MailProperties.class)
public class MailConfiguration {



    @Bean
    @ConditionalOnMissingBean(JavaMailSender.class)
    MailSenderImpl mailSender(MailProperties properties) {
        MailSenderImpl sender = new MailSenderImpl();
        applyProperties(properties, sender);
        return sender;
    }

    private void applyProperties(MailProperties properties, JavaMailSenderImpl sender) {
        sender.setHost(properties.getHost());
        if (properties.getPort() != null) {
            sender.setPort(properties.getPort());
        }
        sender.setUsername(properties.getUsername());
        sender.setPassword(properties.getPassword());
        sender.setProtocol(properties.getProtocol());
        if (properties.getDefaultEncoding() != null) {
            sender.setDefaultEncoding(properties.getDefaultEncoding().name());
        }
        if (!properties.getProperties().isEmpty()) {
            sender.setJavaMailProperties(asProperties(properties.getProperties()));
        }
    }

    private Properties asProperties(Map<String, String> source) {
        Properties properties = new Properties();
        properties.putAll(source);
        return properties;
    }
}

设置属性避免DNS查找

通过源码发现可以设置mail.mime.address.usecanonicalhostname去控制是否去使用DNS查询域名。

那么这种情况我们只需要在启动命令加上-D参数就行，如下

shell 复制代码

java -Dmail.mime.address.usecanonicalhostname=false -Dfile.encoding=UTF8 -Duser.timezone=GMT+8 -jar app.jar

总结

经过以上两手优化，邮件发送速度，从原来的20秒，现在只需要0.5秒左右