feat: update send and batch email method to also support templates

src/main/java/com/resend/services/emails/model/CreateEmailOptions.java

@@ -44,6 +44,9 @@ public class CreateEmailOptions {
     @JsonProperty("scheduled_at")
     private final String scheduledAt;
 
+    @JsonProperty("template")
+    private final Template template;
+
     private CreateEmailOptions(Builder builder) {
         this.from = builder.from;
         this.to = builder.to;
@@ -57,6 +60,7 @@ private CreateEmailOptions(Builder builder) {
         this.html = builder.html;
         this.headers = builder.headers;
         this.scheduledAt = builder.scheduledAt;
+        this.template = builder.template;
     }
 
     /**
@@ -167,6 +171,15 @@ public String getScheduledAt() {
         return scheduledAt;
     }
 
+    /**
+     * Retrieves the template configuration of the email.
+     *
+     * @return The template configuration of the email.
+     */
+    public Template getTemplate() {
+        return template;
+    }
+
     /**
      * Creates a new builder instance to construct CreateEmailOptions.
      *
@@ -192,6 +205,7 @@ public static class Builder {
         private List<Tag> tags;
         private Map<String, String> headers;
         private String scheduledAt;
+        private Template template;
 
         /**
          * Set the 'from' email address.
@@ -528,6 +542,21 @@ public Builder scheduledAt(String scheduledAt) {
             return this;
         }
 
+        /**
+         * Set the template configuration for the email.
+         * <p>
+         * Note: If a template is provided, you cannot send html, text, or react in the payload.
+         * When sending a template, the payload for from, subject, and reply_to take precedence
+         * over the template's defaults for these fields.
+         *
+         * @param template The template configuration.
+         * @return This builder instance for method chaining.
+         */
+        public Builder template(Template template) {
+            this.template = template;
+            return this;
+        }
+
         /**
          * Builds and returns a {@code CreateEmailOptions} based on the configured properties.
          *

src/main/java/com/resend/services/emails/model/Template.java

@@ -0,0 +1,172 @@
+package com.resend.services.emails.model;
+
+import com.fasterxml.jackson.annotation.JsonProperty;
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * Represents a template configuration for sending emails.
+ */
+public class Template {
+
+    @JsonProperty("id")
+    private final String id;
+
+    @JsonProperty("variables")
+    private final Map<String, Object> variables;
+
+    /**
+     * Constructs a Template using the provided builder.
+     *
+     * @param builder The builder to construct the Template.
+     */
+    private Template(Builder builder) {
+        this.id = builder.id;
+        this.variables = builder.variables;
+    }
+
+    /**
+     * Gets the template ID.
+     *
+     * @return The template ID.
+     */
+    public String getId() {
+        return id;
+    }
+
+    /**
+     * Gets the template variables.
+     *
+     * @return The template variables.
+     */
+    public Map<String, Object> getVariables() {
+        return variables;
+    }
+
+    /**
+     * Creates a new builder instance for constructing Template objects.
+     *
+     * @return A new builder instance.
+     */
+    public static Builder builder() {
+        return new Builder();
+    }
+
+    /**
+     * Helper method to create a Variable for use with varargs methods.
+     *
+     * @param key The variable key.
+     * @param value The variable value.
+     * @return A new Variable instance.
+     */
+    public static Variable variable(String key, Object value) {
+        return new Variable(key, value);
+    }
+
+    /**
+     * Represents a template variable with a key and value.
+     */
+    public static class Variable {
+        private final String key;
+        private final Object value;
+
+        /**
+         * Constructs a Variable with the specified key and value.
+         *
+         * @param key The variable key.
+         * @param value The variable value.
+         */
+        public Variable(String key, Object value) {
+            this.key = key;
+            this.value = value;
+        }
+
+        /**
+         * Gets the variable key.
+         *
+         * @return The variable key.
+         */
+        public String getKey() {
+            return key;
+        }
+
+        /**
+         * Gets the variable value.
+         *
+         * @return The variable value.
+         */
+        public Object getValue() {
+            return value;
+        }
+    }
+
+    /**
+     * Builder class for constructing Template objects.
+     */
+    public static class Builder {
+        private String id;
+        private Map<String, Object> variables;
+
+        /**
+         * Set the template ID.
+         *
+         * @param id The template ID (must be a published template).
+         * @return The builder instance.
+         */
+        public Builder id(String id) {
+            this.id = id;
+            return this;
+        }
+
+        /**
+         * Set the template variables.
+         *
+         * @param variables The template variables as key/value pairs.
+         * @return The builder instance.
+         */
+        public Builder variables(Map<String, Object> variables) {
+            this.variables = variables;
+            return this;
+        }
+
+        /**
+         * Add multiple template variables using varargs.
+         *
+         * @param variables The variables to add.
+         * @return The builder instance.
+         */
+        public Builder variables(Variable... variables) {
+            if (this.variables == null) {
+                this.variables = new HashMap<>();
+            }
+            for (Variable variable : variables) {
+                this.variables.put(variable.getKey(), variable.getValue());
+            }
+            return this;
+        }
+
+        /**
+         * Add a single template variable.
+         *
+         * @param key The variable key.
+         * @param value The variable value.
+         * @return The builder instance.
+         */
+        public Builder addVariable(String key, Object value) {
+            if (this.variables == null) {
+                this.variables = new HashMap<>();
+            }
+            this.variables.put(key, value);
+            return this;
+        }
+
+        /**
+         * Build a new Template object.
+         *
+         * @return A new Template object.
+         */
+        public Template build() {
+            return new Template(this);
+        }
+    }
+}

src/test/java/com/resend/services/emails/EmailsTest.java

@@ -218,4 +218,71 @@ public void testListAttachmentsWithPagination_Success() throws ResendException {
         assertEquals(expectedResponse.hasMore(), response.hasMore());
         verify(emails, times(1)).listAttachments(emailId, params);
     }
+
+    @Test
+    public void testSendEmail_WithTemplate_Success() throws ResendException {
+        Template template = Template.builder()
+                .id("template_123")
+                .addVariable("firstName", "John")
+                .addVariable("lastName", "Doe")
+                .addVariable("company", "Acme Corp")
+                .build();
+
+        CreateEmailOptions emailWithTemplate = CreateEmailOptions.builder()
+                .from("Acme <[email protected]>")
+                .to("[email protected]")
+                .subject("Welcome John!")
+                .template(template)
+                .build();
+
+        CreateEmailResponse expectedResponse = EmailsUtil.createSendEmailResponse();
+
+        when(emails.send(emailWithTemplate)).thenReturn(expectedResponse);
+
+        CreateEmailResponse response = emails.send(emailWithTemplate);
+
+        assertNotNull(response);
+        assertEquals(expectedResponse.getId(), response.getId());
+        verify(emails, times(1)).send(emailWithTemplate);
+    }
+
+    @Test
+    public void testSendBatchEmails_WithTemplate_Success() throws ResendException {
+        Template template1 = Template.builder()
+                .id("template_123")
+                .addVariable("firstName", "John")
+                .addVariable("company", "Tech Corp")
+                .build();
+
+        Template template2 = Template.builder()
+                .id("template_123")
+                .addVariable("firstName", "Jane")
+                .addVariable("company", "Design Studios")
+                .build();
+
+        CreateEmailOptions email1 = CreateEmailOptions.builder()
+                .from("Acme <[email protected]>")
+                .to("[email protected]")
+                .subject("Welcome John!")
+                .template(template1)
+                .build();
+
+        CreateEmailOptions email2 = CreateEmailOptions.builder()
+                .from("Acme <[email protected]>")
+                .to("[email protected]")
+                .subject("Welcome Jane!")
+                .template(template2)
+                .build();
+
+        List<CreateEmailOptions> batchEmails = java.util.Arrays.asList(email1, email2);
+        CreateBatchEmailsResponse expectedResponse = EmailsUtil.createBatchEmailsResponse();
+
+        when(batch.send(batchEmails)).thenReturn(expectedResponse);
+
+        CreateBatchEmailsResponse response = batch.send(batchEmails);
+
+        assertNotNull(response);
+        assertEquals(expectedResponse.getData().size(), response.getData().size());
+        verify(batch, times(1)).send(batchEmails);
+    }
 }

src/test/java/com/resend/services/util/EmailsUtil.java

@@ -27,6 +27,35 @@ public static Tag createTag() {
                 .build();
     }
 
+    public static Template createTemplate() {
+        Map<String, Object> variables = new HashMap<>();
+        variables.put("name", "John");
+        variables.put("company", "Acme Corp");
+
+        return Template.builder()
+                .id("template_123")
+                .variables(variables)
+                .build();
+    }
+
+    public static Template createTemplateWithAddVariable() {
+        return Template.builder()
+                .id("template_123")
+                .addVariable("name", "John")
+                .addVariable("company", "Acme Corp")
+                .build();
+    }
+
+    public static Template createTemplateWithVarargs() {
+        return Template.builder()
+                .id("template_123")
+                .variables(
+                        Template.variable("name", "John"),
+                        Template.variable("company", "Acme Corp")
+                )
+                .build();
+    }
+
     public static CreateEmailOptions createEmailOptions() {
         return CreateEmailOptions.builder()
                 .from("Acme <[email protected]>")
@@ -42,6 +71,15 @@ public static CreateEmailOptions createEmailOptions() {
                 .build();
     }
 
+    public static CreateEmailOptions createEmailOptionsWithTemplate() {
+        return CreateEmailOptions.builder()
+                .from("Acme <[email protected]>")
+                .to(Arrays.asList("[email protected]"))
+                .subject("Welcome to Acme")
+                .template(createTemplate())
+                .build();
+    }
+
     public static RequestOptions createRequestOptions() {
         return RequestOptions.builder()
                 .setIdempotencyKey("welcome-user/123456789").build();