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Basic example

Creating a basic HTML structure in j2html is pretty similar to plain HTML. This Java code:

  • version 1.0.0 +
  • earlier versions
html(
    head(
        title("Title"),
        link().withRel("stylesheet").withHref("/css/main.css")
    ),
    body(
        main(attrs("#main.content"),
            h1("Heading!")
        )
    )
)

html().with(
    head().with(
        title("Title"),
        link().withRel("stylesheet").withHref("/css/main.css")
    ),
    body().with(
        main().withId("main").withClass("content").with(
            h1("Heading!")
        )
    )
)

Becomes this HTML:

<html>
    <head>
        <title>Title</title>
        <link rel="stylesheet" href="/css/main.css">
    </head>
    <body>
        <main id="main" class="content">
            <h1>Heading!</h1>
        </main>
    </body>
<html>

It's literally impossible to forget to close a div, mistype an attribute name, or forget an attribute quote! Remember to include the Java wrapping code though, j2html is not a template language, all files are .java. To see how the wrapping code could look, check out the getting started example.

Core concepts

TagCreator.class // Static utility class for creating all tags
import static j2html.TagCreator.*; // Use static star import


Config.class // Holds all configuration.  Offers global configuration or customizable instances
Config.closeEmptyTags = true // Global options are public, static and mutable.
Config.global() // Copy all static Config fields into an instance.  Instances are immutable
Config.defaults() // A Config with defaults that are independent of global options
Config.global().withEmptyTagsClosed(true) // A Config that is different from the global options
Config.defaults().withEmptyTagsClosed(true) // A Config that is different from the default options


TagCreator.join() // Method for joining small snippets, like:
p(join("This paragraph has", b("bold"), "and", i("italic"), "text."))


TagCreator.iff(boolean condition, T ifValue) // If-expression for use in method calls
div().withClasses("menu-element", iff(isActive, "active"))


TagCreator.iffElse(boolean condition, T ifValue, T elseValue) // If/else-expression for use in method calls
div().withClasses("menu-element", iffElse(isActive, "active", "not-active"))


Tag.class // Is extended by ContainerTag (ex <div></div> and EmptyTag (ex <br>)
Tag.attr(String attribute, Object value) // Set an attribute on the tag
Tag.withXyz(String value) // Calls attr with predefined attribute (ex .withId, .withClass, etc.)
Tag.render(HtmlBuilder builder) // Render HTML using the given builder.
Tag.render() // Shortcut for rendering flat HTML into a string using global Config.
ContainerTag.renderFormatted() // Shortcut for rendering indented HTML into a string using global Config.

HtmlBuilder.class // Interface for composing HTML. Implemented by FlatHtml and IndentedHtml
FlatHtml.into(Appendable) // Render into a stream, file, etc. without indentation or line breaks
FlatHtml.into(Appendable appendable, Config config) // Customize rendering of flat html
IndentedHtml.into(Appendable) // Render human-readable HTML into an stream, file, etc.
IndentedHtml.into(Appendable appendable, Config config) // Customize rendering of intended html
ul(li("one"), li("two")).render(IndentedHtml.inMemory()).toString() // Similar to renderFormatted()
ul(li("one"), li("two")).render(IndentedHtml.into(filewriter)) // Write HTML into a file

Loops, each() and filter()

Using Java 8's lambda syntax, you can write loops (via streams) inside your HTML-builder:

  • version 1.0.0 +
  • earlier versions
body(
    div(attrs("#employees"),
        employees.stream().map(employee ->
            div(attrs(".employee"),
                h2(employee.getName()),
                img().withSrc(employee.getImgPath()),
                p(employee.getTitle())
            )
        ).toArray(ContainerTag[]::new)
    )
)

body().with(
    div().withId("employees").with(
        employees.stream().map(employee ->
            div().withClass("employee").with(
                h2(employee.getName()),
                img().withSrc(employee.getImgPath()),
                p(employee.getTitle())
            )
        ).toArray(ContainerTag[]::new)
    )
)

j2html also offers a custom each method, which is slightly more powerful:

  • version 1.0.0 +
  • earlier versions
// each() lets you iterate through a collection and returns the generated HTML
// as a DomContent object, meaning you can add siblings, which is not possible
// using the stream api in the previous example
body(
    div(attrs("#employees"),
        p("Some sibling element"),
        each(employees, employee ->
            div(attrs(".employee"),
                h2(employee.getName()),
                img().withSrc(employee.getImgPath()),
                p(employee.getTitle())
            )
        )
    )
)

// each() lets you iterate through a collection and returns the generated HTML
// as a DomContent object, meaning you can add siblings, which is not possible
// using the stream api in the previous example
body().with(
    div().withId("employees").with(
        p("Some sibling element"),
        each(employees, employee ->
            div().withClass("employee").with(
                h2(employee.getName()),
                img().withSrc(employee.getImgPath()),
                p(employee.getTitle())
            )
        )
    )
)

If you need to filter your collection, j2html has a built in filter function too:

  • version 1.0.0 +
  • earlier versions
// filter() is meant to be used with each(). It just calls the normal
// stream().filter() method, but hides all the boilerplate Java code
// to keep your j2html code neat
body(
    div(attrs("#employees"),
        p("Some sibling element"),
        each(filter(employees, employee -> employee != null), employee ->
            div(attrs(".employee"),
                h2(employee.getName()),
                img().withSrc(employee.getImgPath()),
                p(employee.getTitle())
            )
        )
    )
)

// filter() is meant to be used with each(). It just calls the normal
// stream().filter() method, but hides all the boilerplate Java code
// to keep your j2html code neat
body().with(
    div().withId("employees").with(
        p("Some sibling element"),
        each(filter(employees, employee -> employee != null), employee ->
            div().withClass("employee").with(
                h2(employee.getName()),
                img().withSrc(employee.getImgPath()),
                p(employee.getTitle())
            )
        )
    )
)

Since this is pure Java, all the Employee methods (getName, getImgPath, getTitle) are available to you, and you get autocomplete suggestions and compile time errors.

Given three random employees, all the above approaches would give the same HTML:

<body>
    <div id="employees">
        <div class="employee">
            <h2>David</h2>
            <img src="/img/david.png">
            <p>Creator of Bad Libraries</p>
        </div>
        <div class="employee">
            <h2>Christian</h2>
            <img src="/img/christian.png">
            <p>Fanboi of Jenkins</p>
        </div>
        <div class="employee">
            <h2>Paul</h2>
            <img src="/img/paul.png">
            <p>Hater of Lambda Expressions</p>
        </div>
    </div>
</body>

Two dimensional table example

  • version 1.0.0 +
  • earlier versions
List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 9, 10);
...
table(attr("#table-example"),
    tbody(
        each(numbers, i -> tr(
            each(numbers, j -> td(
                String.valueOf(i * j)
            ))
        ))
    )
)
List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 9, 10);
...
table().withId("table-example").with(
    tbody().with(
        each(numbers, i -> tr().with(
            each(numbers, j -> td().with(
                String.valueOf(i * j)
            ))
        ))
    )
)

The code above is generating this table:

1234567910
24681012141820
369121518212730
4812162024283640
51015202530354550
61218243036425460
71421283542496370
91827364554638190
1020304050607090100

Partials

You can create partials for elements you use a lot:

  • version 1.0.0 +
  • earlier versions
public static Tag enterPasswordInput(String placeholder) {
    return passwordInput("enterPassword", placeholder);
}

public static Tag choosePasswordInput(String placeholder) {
    return passwordInput("choosePassword", placeholder);
}

public static Tag repeatPasswordInput(String placeholder) {
    return passwordInput("repeatPassword", placeholder);
}

public static Tag passwordInput(String identifier, String placeholder) {
    return input()
        .withType("password")
        .withId(identifier)
        .withName(identifier)
        .withPlaceholder(placeholder)
        .isRequired();
}

public static Tag emailInput(String placeholder) {
    return input()
        .withType("email")
        .withId("email")
        .withName("email")
        .withPlaceholder(placeholder)
        .isRequired();
}

public static Tag submitButton(String text) {
    return button(text).withType("submit");
}

public static Tag enterPasswordInput(String placeholder) {
    return passwordInput("enterPassword", placeholder);
}

public static Tag choosePasswordInput(String placeholder) {
    return passwordInput("choosePassword", placeholder);
}

public static Tag repeatPasswordInput(String placeholder) {
    return passwordInput("repeatPassword", placeholder);
}

public static Tag passwordInput(String identifier, String placeholder) {
    return input()
        .withType("password")
        .withId(identifier)
        .withName(identifier)
        .withPlaceholder(placeholder)
        .isRequired();
}

public static Tag emailInput(String placeholder) {
    return input()
        .withType("email")
        .withId("email")
        .withName("email")
        .withPlaceholder(placeholder)
        .isRequired();
}

public static Tag submitButton(String text) {
    return button().withType("submit").withText(text);
}

The equivalent HTML would be:

<input
    type="password"
    id="enterPassword"
    name="enterPassword"
    placeholder="Enter password"
    required
    >

<input
    type="password"
    id="choosePassword"
    name="choosePassword"
    placeholder="Choose password"
    required
    >

<input
    type="password"
    id="repeatPassword"
    name="repeatPassword"
    placeholder="Repeat password"
    required
    >

<input
    type="email"
    id="email"
    name="email"
    placeholder="Email"
    required
    >

<button type="submit">Text</button>

You can then use these partials, for example in a registration form:

  • version 1.0.0 +
  • earlier versions
h1("Please sign up"),
form().withMethod("post").with(
    emailInput("Email address"),
    choosePasswordInput("Choose Password"),
    repeatPasswordInput("Repeat Password"),
    submitButton("Sign up")
)

h1("Please sign up"),
form().withMethod("post").with(
    emailInput("Email address"),
    choosePasswordInput("Choose Password"),
    repeatPasswordInput("Repeat Password"),
    submitButton("Sign up")
)

Pretty clean, right? The rendered HTML is more verbose:

<h1>Please sign up</h1>
<form method="post">
    <input type="email" id="email" name="email" placeholder="Email address" required>
    <input type="password" id="choosePassword" name="choosePassword" placeholder="Choose password" required>
    <input type="password" id="repeatPassword" name="repeatPassword" placeholder="Repeat password" required>
    <button type="submit">Sign up</button>
</form>

Imagine if you wanted labels in addition. The Java snippet would look almost identical: You could create a partial called passwordAndLabel() and nothing but the method name would change. The resulting HTML however, would be twice or thrice as big, depending on whether or not you wrapped the input and label in another tag.

Dynamic views

Once you've set up partials, you can call them from wherever, which greatly reduces potential errors. Let's say we want to include the form from the partials-example in our webpage. We want a header above and a footer below. A lot of templating languages make you do this: 

#include("/path/to/header")
#setTitle("Signup page")
<h1>Please sign up</h1>
<form>
...
</form>
#include("/path/to/footer")

This is a pain to work with. You have no idea what the header and footer expects, and you have no way to affect how they treat your content. You can easily break the site by forgetting to close divs, or by forgetting to include either the header or the footer in one of your views. In j2html you can specify the context in which a view is rendered, and supply the rendering method with type safe parameters! If we want to insert our form in a header/footer frame, we simply create a MainView and make it take our view as an argument:

  • version 1.0.0 +
  • earlier versions
public class MainView {
    public static String render(String pageTitle, Tag... tags) {
        return document(
            html(
                head(
                    title(pageTitle)
                ),
                body(
                    header(
                        ...
                    ),
                    main(
                        tags //the view from the partials example
                    ),
                    footer(
                        ...
                    )
                )
            )
        );
    }
}

MainView.render(
    "Signup page",
    h1("Please sign up"),
    form().withMethod("post").with(
        emailInput("Email address"),
        choosePasswordInput("Choose Password"),
        repeatPasswordInput("Repeat Password"),
        submitButton("Sign up")
    )
);

public class MainView {
    public static String render(String pageTitle, Tag... tags) {
        return document().render() +
            html().with(
                head().with(
                    title(pageTitle)
                ),
                body().with(
                    header().with(
                        ...
                    ),
                    main().with(
                        tags //the view from the partials example
                    ),
                    footer().with(
                        ...
                    )
                )
            ).render();
    }
}

MainView.render(
    "Signup page",
    h1("Please sign up"),
    form().withMethod("post").with(
        emailInput("Email address"),
        choosePasswordInput("Choose Password"),
        repeatPasswordInput("Repeat Password"),
        submitButton("Sign up")
    )
);

Which will result in the rendered HTML:

<html>
    <head>
        <title>Signup page</title>
    </head>
    <body>
    <header>
        ...
    </header>
    <main>
        <h1>Please sign up</h1>
        <form method="post">
            <input type="email" id="email" name="email" placeholder="Email address" required>
            <input type="password" id="choosePassword" name="choosePassword" placeholder="Choose password" required>
            <input type="password" id="repeatPassword" name="repeatPassword" placeholder="Repeat password" required>
            <button type="submit">Sign up</button>
        </form>
    </main>
    <footer>
        ...
    </footer>
    </body>
</html>

We would now get a compilation error if we forgot to include a title, and there is 0 chance of forgetting either header or footer, mistyping paths, forgetting to close divs, or anything else.

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