通过 Maroto 在 Golang 中生成 PDF 来进行长期操作

作者：Subha Chanda✏️

Go，也称为 Golang，是由 Google 设计的静态类型、编译型编程语言。它结合了静态类型语言的性能和安全性优势以及通常与动态类型语言相关的易用性。

由于其并发性和多线程机制以及出色的标准库，Go 成为各种应用程序的流行选择，包括 Web 开发、网络编程和系统编程。

PDF 生成是各种类型的应用程序所需的一项重要任务。大规模高效地生成 PDF 可能是一项复杂的任务。然而，以其性能和效率而闻名的 Go 可能是在大批量场景中生成 PDF 的不错选择。

但是，编写自己的 PDF 生成器可能是一项复杂的工作。这就是马罗托发挥作用的地方。它是一个 PDF 生成库，灵感来自 Bootstrap 的布局系统。

具有行和列的网格系统使布局管理更加容易。它还支持自动分页以处理内容溢出。您还可以获得对文本、图像、条形码、QR 码、签名等的内置支持。

我将撰写有关如何在 Maroto 的帮助下在 Golang 中创建动态 PDF 的文章。

为什么我们需要PDF生成？

PDF 生成功能对于许多类型的项目和应用程序都非常有价值。

• 发票系统 - 自动生成 PDF 发票并将其发送给客户，可以确保格式的一致性，并允许轻松定制发票模板
• 报告工具 — PDF 生成对于创建业务分析、财务报表或项目状态更新的详细报告至关重要
• 票务系统 — 生成 PDF 门票对于旅行预订、活动入场或电影放映确认至关重要
• 标签创建 - 动态生成用于运输、产品标签或组织目的的标签，确保清晰准确地呈现正确的信息
• 证书生成 - 自动创建课程完成证书、奖项或认证，可以轻松定制和个性化每个证书
• 合同管理 — 根据特定条款或条件生成具有动态内容的法律文件或合同，简化了创建准确和个性化协议的过程

您可以想象其他用例，并了解为什么自动化 PDF 可确保一致性并提供专业外观的格式。

在 Golang 中使用 Maroto 之前需要了解什么

在继续之前，请确保您已记下以下内容：

• 对 Go 的基本了解
• Go 安装在您的计算机上，最好是最新版本，在撰写本文时为 1.22.2
• 您首选的 IDE 或文本编辑器 — 我推荐 Visual Studio
• 为您的 IDE 扩展（如果可用）

如果您需要熟悉 Go，您可以按照本指南来获得对该语言的基本了解。如果一切准备就绪，您就可以出发了。 ？

使用 Maroto 生成 PDF

首先，我们先讨论一些在使用 Maroto 生成 PDF 时发挥关键作用的核心概念。

排

由高度定义，行代表文档的水平部分。它可以包含多个列 (Col)。 New 函数初始化具有指定高度的 Row。

上校

列代表行内的垂直部分，可以包含各种组件，例如文本、图像、二维码或条形码。栏目在内容和大小方面都很灵活。 Col 的 New 函数可以创建具有特定大小或最大大小（如果未提供大小）的列。 Add 方法允许将组件添加到列中。

成分

这是各种文档元素实现的接口。文本、图像、QR 码和条形码等元素被视为组件。可以将它们添加到列中以构建文档内容。现在让我们启动一个Go项目。

初始化一个新的Go项目并安装依赖项

首先，打开您最喜欢的代码编辑器，然后打开编辑器中的文件夹，您将在其中保存与项目相关的所有代码。

现在打开终端窗口，找到项目位置，然后运行以下命令：

go mod init github.com/USERNAME/PROJECT_NAME

在上面的命令中，将 github.com 替换为您存储文件的域，例如 Bitbucket 或 Gitlab。此外，将 USERNAME 替换为您的用户名，将 PROJECT_NAME 替换为所需的项目名称。

Running this command will initialize a Go project and will create a go.mod file in the folder. This file is used to manage the dependencies of a Go project.

After the command creates a go.mod file successfully, you are ready to install the necessary packages. The only package required to follow along with this article is Maroto.

To install Maroto as a dependency, run the following command:

go get github.com/johnfercher/maroto/v2@v2

At the time of writing this article, Maroto is in its v2 stage. And, the v2 provides significant performance improvements compared to v1.

All of the logic for this code will reside in the main package. To keep the article simple, everything will be in a single file. For writing code, create a new file called main.go to the root of your project folder, and paste the following code into it:

package main

import "fmt"

func main() {
 fmt.Println("Hello, World!")
}

Now, run the command go run main.go from the terminal, and check if it prints Hello, World! in the terminal. If it does, it means you are ready to get started.

Building the application

In this article, we’ll be building a sample PDF that replicates a ticket copy. The PDF will contain a dynamic QR code, as well as a barcode, image, and other relevant details.

The core layout of Maroto is based on the 12-unit grid system. Meaning that, the width of each page is divided into an equal amount of 12 units. Based on this, you can add a structure to your PDF.

The image shown below replicates a basic ticket of a movie show, and you’ll be creating this PDF programmatically using Go:  

The ticket contains three basic sections: header, body, and footer.

The header contains a logo, name and address of an imaginary company called Showbees Ticketing.

The body contains all the necessary tickets like the name of the show, language, date, venue, number of tickets, etc.. The body also contains a QR code and a barcode just to demonstrate how these can be implemented in your PDF.

The footer is very basic and contains a single text.

Let’s start by creating a struct that defines the structure of the PDF. Copy and paste the code in your main.go file:

package main

type Company struct {
    Name         string
    Address      string
    LogoLocation string
}

type Ticket struct {
    ID                 int
    ShowName           string
    ShowTime           string
    Language           string
    ShowVenue          string
    SeatNumber         string
    Cost               float64
    Screen             string
    TicketCount        int
    ShowPosterLocation string
}

func main() {
    c := Company{
        Name:         "ShowBees Ticketing",
        Address:      "1234 Main St, City, State 12345",
        LogoLocation: "./logo.png",
    }

    t := Ticket{
        ID:                 1,
        ShowName:           "Planet of the Gophers: The War Begins",
        ShowTime:           "Sat 01/01/2022 7:00 PM",
        Language:           "English",
        ShowVenue:          "Gophedorium",
        SeatNumber:         "Platinum - A1, A2",
        Cost:               620.00,
        Screen:             "Screen 1",
        TicketCount:        2,
        ShowPosterLocation: "./poster.png",
    }
}

Here, we are creating a Company struct first. This represents the details of the company. The Ticket struct defines the structure for the ticket.

In the main function, we are creating a variable called c which holds the company details and another variable called t which holds the ticket details. The field name, and the variable are pretty self-explanatory.

One thing to mention here is that the logo and the poster are stored in the root of the folder. If you are following along, you can either add any two images in this place, or you can download the images of the article from this repo.

Now, let’s create the header.

Creating a header

To create a header, we’ll be creating a new function. The function will take a parameter of type Company and will return a core.Row. The header is pretty simple. Let’s check out the code first:

func getPageHeader(c Company) core.Row {
    return row.New(16).Add(
        image.NewFromFileCol(4, c.LogoLocation, props.Rect{
            Center:  false,
            Percent: 100,
        }),
        col.New(2),
        col.New(6).Add(
            text.New(c.Name, props.Text{
                Style: fontstyle.Bold,
                Size:  10,
            }),
            text.New(c.Address, props.Text{
                Top:  6,
                Size: 10,
            }),
        ),
    )
}

The header consists of three columns: an image column, an empty column, and a column containing text components. Let’s look at the code step-by-step.

The first line row.New(16) creates a new row component with a height of 16. This row will serve as the container for the header columns.

To render the image, you’ll need to use the image.NewFromFileCol method. This function is available in the image component.

This line image.NewFromFileCol(4, c.LogoLocation, props.Rect{...}) creates an image column with a size of 4. It loads an image from the file specified by c.LogoLocation and sets some properties for the image, such as its alignment and size.

The next line col.New(2) creates an empty column with a size of 2. This column is used to create space between the image column and the text column.

The following line col.New(6).Add(...) creates a column with a size of 6.

Inside this column, there are two text components created using the text.New function. The first text component displays the company name (c.Name) with some text properties like bold style, left alignment, and font size of 10.

The second text component displays the company address (c.Address) with different text properties, including a top margin of 6 pixels, left alignment, and font size of 10.

Finally, the image column and the text column are then added to the row using the Add method. So, a row contains all the columns, and columns can be added in a row.

Let’s now create a function called getMaroto which will be responsible for registering necessary components and returning a core.Maroto interface which wraps the basic methods of Maroto.

Using the methods from these interfaces, we’ll be generating the PDF from the main function. Let’s take a look at the function first:

func getMaroto(c Company, t Ticket) core.Maroto {
    cfg := config.NewBuilder().WithDimensions(120, 200).Build()

    mrt := maroto.New(cfg)

    err := mrt.RegisterHeader(getPageHeader(c))

    if err != nil {
        log.Println("Error registering header")
    }

    return mrt
}

At this point, we only have a header component. As we add more components to the PDF, this function will grow larger. The function takes two parameters: a company object and a ticket object.

The function begins by creating a new PDF configuration using config.NewBuilder(), which is customized with width and height for the PDF document through the WithDimensions method. This configuration is then used to instantiate a new Maroto PDF document (mrt) with the specified dimensions.

After setting the desired configuration options, Build() is called to finalize and return the configuration object.

If you do not prefer to set up dimensions like we have done in this article and want to use a standard paper size, Maroto provides a WithPageSize function as well where you can add a standard page size like A4, Letter, etc..

Here’s a sample:

cfg := config.NewBuilder().WithPageSize(pagesize.Letter).Build()

After the cfg variable is initialized, it’s time to register the header for the PDF document. This is done by calling mrt.RegisterHeader(getPageHeader(c)), where getPageHeader(c) generates a header row based on the provided Company object.

The RegisterHeader method adds the header row to the PDF and calculates its height to ensure it fits within the page's useful area. If the header's height exceeds the available space, an error is logged, and the mrt variable is returned from the function.

Update the main function as shown below:

func main() {
  // ...
    // ...

    m := getMaroto(c, t)

    document, err := m.Generate()

    filename := fmt.Sprintf("ticket-%d.pdf", t.ID)

    if err != nil {
        log.Println("Error generating PDF")
    }

    // Check if temp folder exists, if not create it
    if _, err := os.Stat("temp"); os.IsNotExist(err) {
        err = os.Mkdir("temp", 0755)
        if err != nil {
            log.Println("Error creating directory:", err)
        }
    }

    err = document.Save("temp/" + filename)
    if err != nil {
        log.Println("Unable to save file:", err)
    }
}

The code here is pretty straightforward. The company and ticket details are passed into the getMaroto function. The Generate method of the Maroto type is then called to actually generate the PDF document.

After generating the PDF, a filename for the PDF is created using the fmt.Sprintf function, incorporating the ticket's ID into the filename. It then checks if a "temp" directory exists using os.Stat, and if it doesn't, the directory is created with os.Mkdir with appropriate permissions. If any error occurs in this stage, the error is logged in.

Finally, the generated PDF document is saved to the temp directory using the Save method, which internally uses os.WriteFile to write the PDF bytes to a file. The permissions for the file are set to allow any operation by the user.

If you run the code using go run main.go, you’ll be able to see that a new folder called temp is created, and the folder contains a file called ticket-1.pdf. Your PDF should look like this image now:

Let’s move on and create the body of the PDF. This is the longest of the functions, but now that you understand the basics of how Maroto works, it should be a breeze.

Creating a body

Create a new function called getShowDetails which accepts a ticket struct and returns an array of core.Row interface. First, copy and paste the below code into your main.go function:

func getShowDetails(t Ticket) []core.Row {
    rows := []core.Row{
        row.New(30).Add(
            image.NewFromFileCol(4, t.ShowPosterLocation, props.Rect{
                Center:  true,
                Percent: 100,
            }),
            col.New(8).Add(
                text.New(t.ShowName, props.Text{
                    Style: fontstyle.Bold,
                    Size:  10,
                }),
                text.New(t.Language, props.Text{
                    Top:   6,
                    Style: fontstyle.Normal,
                    Size:  8,
                    Color: &props.Color{Red: 95, Green: 95, Blue: 95},
                }),
                text.New(t.ShowTime, props.Text{
                    Top:   12,
                    Style: fontstyle.Bold,
                    Size:  10,
                }),
                text.New(t.ShowVenue, props.Text{
                    Top:   18,
                    Style: fontstyle.Normal,
                    Size:  8,
                    Color: &props.Color{Red: 95, Green: 95, Blue: 95},
                }),
            ),
        ),
        row.New(6),
        row.New(1).Add(
            line.NewCol(12, props.Line{
                Thickness:   0.2,
                Color:       &props.Color{Red: 200, Green: 200, Blue: 200},
                SizePercent: 100,
                Style:       linestyle.Dashed,
            }),
        ),
        row.New(3),
        row.New(16).Add(
            col.New(2).Add(
                text.New(strconv.Itoa(t.TicketCount), props.Text{
                    Style: fontstyle.Bold,
                    Size:  24,
                    Align: align.Center,
                }),
                text.New("Tickets", props.Text{
                    Top:   12,
                    Style: fontstyle.Normal,
                    Size:  8,
                    Color: &props.Color{Red: 95, Green: 95, Blue: 95},
                    Align: align.Center,
                }),
            ),
            col.New(2),
            col.New(8).Add(
                text.New(t.Screen, props.Text{
                    Size:  8,
                    Color: &props.Color{Red: 95, Green: 95, Blue: 95},
                }),
                text.New(t.SeatNumber, props.Text{
                    Top:   6,
                    Style: fontstyle.Bold,
                    Size:  14,
                }),
            ),
        ),
        row.New(3),
        row.New(1).Add(
            line.NewCol(12, props.Line{
                Thickness:   0.2,
                Color:       &props.Color{Red: 200, Green: 200, Blue: 200},
                SizePercent: 100,
                Style:       linestyle.Dashed,
            }),
        ),
        row.New(6),
        row.New(20).Add(
            code.NewQrCol(12,
                fmt.Sprintf("%v\n%v\n%v\n%v", t.ID, t.ShowName, t.ShowTime, t.ShowVenue),
                props.Rect{
                    Center:  true,
                    Percent: 100,
                },
            ),
        ),
        row.New(10).Add(
            col.New(12).Add(text.New(fmt.Sprintf("Booking ID: %v", t.ID), props.Text{
                Style: fontstyle.Normal,
                Size:  8,
                Align: align.Center,
                Top:   2,
            })),
        ),
        row.New(1).Add(
            line.NewCol(12, props.Line{
                Thickness:   0.2,
                Color:       &props.Color{Red: 200, Green: 200, Blue: 200},
                SizePercent: 100,
                Style:       linestyle.Solid,
            }),
        ),
        row.New(3),
        row.New(10).Add(
            code.NewBarCol(12, strconv.Itoa(t.ID),
                props.Barcode{
                    Center:  true,
                    Percent: 100,
                },
            ),
        ),
    }

    return rows
}

The code starts by initializing a new variable called rows, which consists of all the rows that will be returned from the function.

The rows slice starts by initializing a first row of height 30. In this row, an image is first added to the column which takes a third of the available area. The t.ShowPosterLocation is rendered here, with a few properties like centre alignment and size in percentage.

In the remaining 2/3rd space, a new column is added, which renders the show name, show language and the show time. Each of the text has a different size, top position, and color. For defining the colors, the props.Color struct is used, where the value of red, green, and blue is defined.

The next row is added to add a blank space in the PDF. After the blank space, a new line is added to the rows slice. A new line can be added using the line module available in the Maroto package.

The line.NewCol function takes two arguments, one being the area to be taken, and another one for defining the properties of the line. In this case, the line takes the complete width, and different properties like the thickness, color, and size are defined. For the style, a dashed line is added.

After adding the line, another empty row is added, and after the empty row, the ticket count, screen name, and seat number are added.

Similar to the other columns, different props for the text are added for enhancing the look of the document. To display the ticket count, you must have noticed that we are using the strconv package to convert the integer type to string because the text.New function takes the value as a string.

A blank space area and a line is added to the document after the details.

In the next step, a new row of size 20 is created. Inside this row, a column is added. This column contains a QR code generated from a formatted string that includes the ticket ID, show name, show time, and show venue.

The QR code is centered and occupies 100 percent of the column's width. The NewQrCol function is used to create this column by generating a QR code with the specified properties and adding it to a new column of a specified size.

Next, a new row with a height of 10 units is created, and a column is added to it. This column contains a text component displaying the booking ID with centered positioning. Following that, a row with a height of 1 unit is added, containing a single column with a line.

The line's color, thickness, and style are specified, and it spans 100 percent of the column's width. This is used as a separator between sections of the document. An empty row with a height of 3 units is then added to create some vertical spacing in the document.

Finally, a row with a height of 10 units is created, containing a column. The column contains a barcode generated from the ticket ID. The barcode is generated using the code.NewBarCol function. It is centered and occupies 100 percent of the column's width.

With the above complete, let’s move on to the footer.

Creating a footer

The footer contains just a single text. The aim is to demonstrate how a footer can be registered in your PDF:

func getPageFooter() core.Row {
    return row.New(2).Add(
        col.New(12).Add(
            text.New("Powered by ShowBees Ticketing System", props.Text{
                Style: fontstyle.Italic,
                Size:  8,
                Align: align.Center,
                Color: &props.Color{Red: 255, Green: 120, Blue: 218},
            }),
        ),
    )
}

The footer displays a single text in a column. The text has a size of 8 pixels, center aligned with an RGB color value.

Now, to register this footer and the getShowDetails function into the getMaroto function, update this accordingly:

func getMaroto(c Company, t Ticket) core.Maroto {
    cfg := config.NewBuilder().WithDimensions(120, 200).Build()

    // ...
    // ...

    mrt.AddRow(6)

    mrt.AddRow(4, line.NewCol(12, props.Line{
        Thickness:   0.2,
        Color:       &props.Color{Red: 200, Green: 200, Blue: 200},
        SizePercent: 100,
    }))

    mrt.AddRow(6)

    mrt.AddRows(getShowDetails(t)...)

    mrt.AddRow(8)

    err = mrt.RegisterFooter(getPageFooter())

    if err != nil {
        log.Println("Error registering footer")
    }

    return mrt
}

If you generate the PDF by running go run main.go, you should get a PDF that resembles the image shown earlier in the article. Here is a video demonstration of the PDF generation.

The complete code for the article is available in this GitHub repo.

What makes Maroto stand out?

Maroto uses a grid system similar to Bootstrap, making it intuitive for developers familiar with web development. This system allows for easy layout management using rows and columns, which can contain various components like text, images, QR codes, and barcodes.

Maroto makes it easy for developers to create complex PDF layouts without extensive boilerplate code, a significant advantage over more complex libraries like UniDoc and pdfcpu.

Maroto is built on top of gofpdf but offers significant performance improvements, especially in v2. This makes it suitable for high-volume PDF generation tasks.

Maroto also handles content overflow by automatically adding page breaks without manual intervention.

Finally, Maroto has a growing community and comprehensive documentation. The library is open-source and actively maintained, which ensures that it stays up-to-date with the latest features and improvements.

Conclusion

Generating PDF documents using the Maroto library in Go is a straightforward and efficient process. This powerful library provides an intuitive API that allows developers to create complex layout structures with ease.

The use of rows and columns to manage content positioning, alongside the built-in support for various elements such as text, images, QR codes, and barcodes, makes Maroto a highly versatile tool.

To explore more about the package, you can check out their documentation.

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