Add endpoint to stream data read from database

build.gradle

@@ -2,6 +2,7 @@ plugins {
     id 'org.springframework.boot' version '3.3.4'
     id 'io.spring.dependency-management' version '1.1.0'
     id 'java'
+    id("io.freefair.lombok") version "8.10.2"
 }
 
 targetCompatibility = '22'
@@ -14,6 +15,10 @@ repositories {
 dependencies {
     implementation 'org.springframework.boot:spring-boot-starter-web'
     testImplementation('org.springframework.boot:spring-boot-starter-test')
+
+    implementation("org.springframework.boot:spring-boot-starter-jooq")
+    implementation('org.flywaydb:flyway-core')
+    runtimeOnly('com.h2database:h2')
 }
 
 test {

src/main/java/com/wilkins/showcase/Book.java

@@ -0,0 +1,4 @@
+package com.wilkins.showcase;
+
+public record Book(String id, String name, String author) {
+}

src/main/java/com/wilkins/showcase/controller/BookController.java

@@ -0,0 +1,31 @@
+package com.wilkins.showcase.controller;
+
+import com.wilkins.showcase.service.BookService;
+import lombok.RequiredArgsConstructor;
+import lombok.extern.slf4j.Slf4j;
+import org.apache.coyote.http11.Constants;
+import org.springframework.http.HttpHeaders;
+import org.springframework.http.ResponseEntity;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.bind.annotation.RestController;
+import org.springframework.web.servlet.mvc.method.annotation.StreamingResponseBody;
+
+import static org.springframework.http.ResponseEntity.ok;
+
+@RestController
+@RequestMapping("/books")
+@Slf4j
+@RequiredArgsConstructor
+public class BookController {
+
+    private final BookService bookService;
+
+    @GetMapping
+    ResponseEntity<StreamingResponseBody> streamBooks() {
+        log.info("streaming books");
+        return ok()
+                .header(HttpHeaders.CONTENT_ENCODING, Constants.CHUNKED)
+                .body(bookService::streamBooks);
+    }
+}

src/main/java/com/wilkins/showcase/controller/JsonBook.java

@@ -0,0 +1,9 @@
+package com.wilkins.showcase.controller;
+
+import com.wilkins.showcase.Book;
+
+public record JsonBook(String id, String name, String author) {
+    public static JsonBook from(Book book) {
+        return new JsonBook(book.id(), book.name(), book.author());
+    }
+}

src/main/java/com/wilkins/showcase/service/BookRepository.java

@@ -0,0 +1,9 @@
+package com.wilkins.showcase.service;
+
+import com.wilkins.showcase.Book;
+
+import java.util.stream.Stream;
+
+public interface BookRepository {
+    Stream<Book> findAll();
+}

src/main/java/com/wilkins/showcase/service/BookService.java

@@ -0,0 +1,7 @@
+package com.wilkins.showcase.service;
+
+import java.io.OutputStream;
+
+public interface BookService {
+    void streamBooks(OutputStream outputStream);
+}

src/main/java/com/wilkins/showcase/service/DefaultBookService.java

@@ -0,0 +1,37 @@
+package com.wilkins.showcase.service;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.wilkins.showcase.controller.JsonBook;
+import lombok.RequiredArgsConstructor;
+import lombok.extern.slf4j.Slf4j;
+import org.springframework.stereotype.Service;
+
+import java.io.IOException;
+import java.io.OutputStream;
+
+@RequiredArgsConstructor
+@Slf4j
+@Service
+public class DefaultBookService implements BookService {
+    private final ObjectMapper objectMapper = new ObjectMapper();
+    private final BookRepository bookRepository;
+
+    @Override
+    public void streamBooks(OutputStream outputStream) {
+        try (var books = bookRepository.findAll()) {
+            books
+                    .map(JsonBook::from)
+                    .forEach(book -> {
+                        try {
+                            log.info("getting book {}", book);
+                            Thread.sleep(2000);
+                            log.info("writing book {}", book.name());
+                            outputStream.write(objectMapper.writeValueAsBytes(book));
+                            outputStream.flush();
+                        } catch (IOException | InterruptedException e) {
+                            throw new RuntimeException(e);
+                        }
+                    });
+        }
+    }
+}

src/main/java/com/wilkins/showcase/service/JooqBookRepository.java

@@ -0,0 +1,40 @@
+package com.wilkins.showcase.service;
+
+import com.wilkins.showcase.Book;
+import org.jooq.DSLContext;
+import org.jooq.Field;
+import org.jooq.Record;
+import org.jooq.Table;
+import org.jooq.impl.DSL;
+import org.springframework.stereotype.Service;
+
+import javax.sql.DataSource;
+import java.sql.SQLException;
+import java.util.List;
+import java.util.stream.Stream;
+
+import static org.jooq.impl.DSL.field;
+
+@Service
+public class JooqBookRepository implements BookRepository {
+
+    private final DSLContext dsl;
+
+    public JooqBookRepository(DataSource dataSource) throws SQLException {
+        this.dsl = DSL.using(dataSource.getConnection());
+    }
+
+    @Override
+    public Stream<Book> findAll() {
+        return dsl.select(bookFields)
+                .from(bookTable)
+                .fetchStreamInto(Book.class);
+    }
+
+    private static final Table<Record> bookTable = DSL.table("book");
+    private static final Field<String> externalId = field("book.external_id", String.class);
+    private static final Field<String> title = field("book.title", String.class);
+    private static final Field<String> author = field("book.author", String.class);
+    private static final List<Field<String>> fields = List.of(externalId, title, author);
+    private static final Field[] bookFields = fields.toArray(new Field[0]);
+}

src/main/resources/application.yml

@@ -1,4 +1,13 @@
 server:
   port: 8080
   servlet:
-    application-display-name: showcase
+    application-display-name: showcase
+
+spring:
+  h2:
+    console:
+      enabled: true
+  datasource:
+    url: jdbc:h2:mem:showcase
+    username: showcase
+    password: Passw0rd!

src/main/resources/db/migration/V0__create_book.sql

@@ -0,0 +1,28 @@
+create table book
+(
+    id          bigint       not null auto_increment,
+    external_id varchar(120) not null,
+    title       varchar(120),
+    author      varchar(120),
+    constraint book_pk primary key (id),
+    constraint book_external_id unique (external_id)
+);
+
+insert into book(external_id, title, author)
+values ('hobbit_01', 'The Hobbit', 'JRR Tolkien');
+insert into book(external_id, title, author)
+values ('lord_01', 'Fellowship of the Ring', 'JRR Tolkien');
+insert into book(external_id, title, author)
+values ('lord_02', 'The Two Towers', 'JRR Tolkien');
+insert into book(external_id, title, author)
+values ('lord_03', 'Return of the King', 'JRR Tolkien');
+insert into book(external_id, title, author)
+values ('madding_01', 'Far from the Madding Crowd', 'Thomas Hardy');
+insert into book(external_id, title, author)
+values ('merchant_01', 'The Merchant of Venice', 'William Shakespear');
+insert into book(external_id, title, author)
+values ('hamlet_01', 'Hamlet', 'William Shakespear');
+insert into book(external_id, title, author)
+values ('romeo_01', 'Romeo and Juliet', 'William Shakespear');
+insert into book(external_id, title, author)
+values ('macbeth_01', 'Macbeth', 'William Shakespear');