groovy.lang.GroovyRuntimeException 发送电子邮件

Question

我正在尝试从 groovy 脚本发送电子邮件。我给出了以下代码：

import org.apache.commons.net.smtp.*

port = 25
org = 'mycompany.org'


client = new SMTPClient()
client.connect('<server_name>', port)
client.login()

// set sender and recipient
client.sender = "<email_address>"
client.addRecipient("<email_address>")

// create and send header information
header = new SimpleSMTPHeader("<email_address>",
        "<email_address>", 'Successful build')
header.addCC("<email_address>")
header.addHeaderField('Organization', org)
writer = new PrintWriter(client.sendMessageData())
writer << header

// send body of message
writer << 'Successful build for ' + new Date()
writer.close()

client.logout()
client.disconnect()

fixture.assertEmailArrived(from: "cruise@$org",
                           subject: 'Successful build')

我正在使用 apache 的 commons-net-2.0.jar 来运行代码。错误信息如下：

Caught: groovy.lang.GroovyRuntimeException: Ambiguous method overloading for method java.io.PrintWriter#<init>.
Cannot resolve which method to invoke for [null] due to overlapping prototypes between:
    [class java.lang.String]
    [class java.io.File]
    [class java.io.Writer]
    [class java.io.OutputStream]
groovy.lang.GroovyRuntimeException: Ambiguous method overloading for method java.io.PrintWriter#<init>.
Cannot resolve which method to invoke for [null] due to overlapping prototypes between:
    [class java.lang.String]
    [class java.io.File]
    [class java.io.Writer]
    [class java.io.OutputStream]
    at TestEmail.run(TestEmail.groovy:20)

错误似乎来自这部分代码：

writer = new PrintWriter(client.sendMessageData())

我试图打印出 client.sendMessageData() 并且该值显示为 null。理想情况下，它应该是一些表示 Writer 对象的值。请帮我解决问题。

Answer 1

问题如下：

new PrintWriter(client.sendMessageData())

我认为如果命令由于某种原因失败，sendMessageData 会返回 null。当您将null 传递给PrintWriter 构造函数时，Groovy 的动态调度机制无法知道您尝试调用哪个构造函数。你可以这样做：

new PrintWriter((Writer)client.sendMessageData())

这将消除模棱两可的方法重载问题，但仍然可能不是您想要的。您可能希望在实例化 PrintWriter 之前检查返回值是否为 null。