我创建了一个Spring Boot微服务,它发出HTTP GET请求从MySQL数据库中提取数据(每个节点),该数据在单个基于邻接列表树的表中设置。
我能够获取特定级别节点的子节点,但还需要能够查看所有子节点(即使这需要不同的REST调用和服务方法)。
我在我的技术栈中使用Java 1.8、Spring Boot 1.5.6.RELEASE、JPA和MySQL 5。
然而,它仅提供了第一级(而非 Books & Coffee 和 Latte 下面的子节点):
尝试列出 Coffee 的所有子元素时:
JSON响应有效负载:
我可以翻译中文。
我能够获取特定级别节点的子节点,但还需要能够查看所有子节点(即使这需要不同的REST调用和服务方法)。
我在我的技术栈中使用Java 1.8、Spring Boot 1.5.6.RELEASE、JPA和MySQL 5。
pom.xml:
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>1.5.6.RELEASE</version>
</parent>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
<java.version>1.8</java.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
<dependency>
<groupId>javax.xml.bind</groupId>
<artifactId>jaxb-api</artifactId>
<version>2.3.0</version>
</dependency>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<scope>runtime</scope>
</dependency>
</dependencies>
Node.java(POJO):
@Entity
public class Node {
@Id
@GeneratedValue(strategy=GenerationType.IDENTITY)
private Long id;
@NotNull
private String name;
@Column(name = "parent_id")
private Long parentId;
// Getters & Setters Omitted for Brevity
}
NodeRepository:
@Repository
public interface NodeRepository extends JpaRepository<Node, Long> {
@Query(value = "SELECT * FROM NODE WHERE parent_id = ?", nativeQuery = true)
List<Node> findNodesByParentId(Long parentId);
@Query(value = "SELECT * FROM NODE WHERE name = ?", nativeQuery = true)
Node findByName(String name);
}
我的服务:
public interface MyService {
List<Node> getHierarchyPerNode(Node node);
void removeNode(String node);
}
MyServiceImpl:
@Service
public class MyServiceImpl implements MyService {
@Autowired
NodeRepository repository;
@Override
public List<Node> getHierarchyPerNode(Node node) {
List<Node> nodes = new ArrayList<>();
List<Node> children = new ArrayList<>();
if (node != null) {
Node aNode = repository.findByName(node.getName());
nodes.add(aNode);
Long parentId = aNode.getId();
children = repository.findNodesByParentId(parentId);
// Was trying this as recursion but kept throwing an NullPointerException.
// for (Node child : children) {
// return getHierarchyPerNode(child);
// }
}
if (!children.isEmpty()) {
return children;
}
else {
return nodes;
}
}
}
RestController:
@RestController
public class RestController {
private HttpHeaders headers = null;
@Autowired
MyService myService;
public RestController() {
headers = new HttpHeaders();
headers.add("Content-Type", "application/json");
}
@RequestMapping(
value = {"/api/nodes"},
method = RequestMethod.GET,
produces = "APPLICATION/JSON"
)
public ResponseEntity<Object> getHierarchyPerNode(Node node) {
if (null == node) {
return new ResponseEntity<Object>(HttpStatus.NOT_FOUND);
}
List<Node> nodes = myService.getHierarchyPerNode(node);
if (null == nodes) {
return new ResponseEntity<Object>(HttpStatus.NOT_FOUND);
}
return new ResponseEntity<Object>(nodes, headers, HttpStatus.OK);
}
}
DatabasePopulator(在Spring Boot启动期间使用此选项来填充数据库):
@Component
public class DatabasePopulator implements ApplicationListener<ContextRefreshedEvent> {
private final NodeRepository repository;
public DatabasePopulator(NodeRepository repository) {
this.repository = repository;
}
@Override
public void onApplicationEvent(ContextRefreshedEvent event) {
Node root = new Node();
root.setName("Store");
root.setParentId(null);
repository.save(root);
// Populate Books Node (along with children)
Node books = new Node();
books.setName("Books");
books.setParentId(root.getId());
repository.save(books);
Node horror = new Node();
horror.setName("Horror");
horror.setParentId(books.getId());
repository.save(horror);
Node romance = new Node();
romance.setName("Romance");
romance.setParentId(books.getId());
repository.save(romance);
Node fantasy = new Node();
fantasy.setName("Fantasy");
fantasy.setParentId(books.getId());
repository.save(fantasy);
// Populate Coffee Node (along with children)
Node coffee = new Node();
coffee.setName("Coffee");
coffee.setParentId(root.getId());
repository.save(coffee);
Node mocha = new Node();
mocha.setName("Mocha");
mocha.setParentId(coffee.getId());
repository.save(mocha);
Node latte = new Node();
latte.setName("Latte");
latte.setParentId(coffee.getId());
repository.save(latte);
// Populate show espresso as a child underneath the Latte node.
Node espresso = new Node();
espresso.setName("Espresso");
espresso.setParentId(latte.getId());
repository.save(espresso);
}
}
显然,所填充的数据代表了数据库中的这棵树:
Store
|______ Books
|
|______Horror
|
|______Romance
|
|______Fantasy
|______Coffee
|
|______Mocha
|
|______Latte
|
|_____Espresso
观察 / 问题:
通过我的RestController,调用这个REST端点,我可以获取第一级记录:
http://localhost:8080/myapp/api/nodes?name=Products
然而,它仅提供了第一级(而非 Books & Coffee 和 Latte 下面的子节点):
[
{
"id": 2,
"name": "Books",
"parentId": 1
},
{
"id": 6,
"name": "Coffee",
"parentId": 1
}
]
在书籍分类下,不再列出恐怖、浪漫和幻想等子类别,在咖啡分类下,不再将摩卡、拿铁(以及拿铁下的浓缩咖啡)作为子类别。
现在,如果使用parentNode(例如Books),它会显示子级(但仅限第一级):
http://localhost:8080/myapp/api/nodes?name=Books
JSON响应有效载荷:
[
{
"id": 3,
"name": "Horror",
"parentId": 2
},
{
"id": 4,
"name": "Romance",
"parentId": 2
},
{
"id": 5,
"name": "Fantasy",
"parentId": 2
}
]
尝试列出 Coffee 的所有子元素时:
http://localhost:8080/myapp/api/nodes?name=Coffee
JSON响应有效负载:
[
{
"id": 7,
"name": "Mocha",
"parentId": 6
},
{
"id": 8,
"name": "Latte",
"parentId": 6
}
]
看,这个没有显示Espresso,必须调用Latte作为父级来显示:
http://localhost:8080/myapp/api/nodes?name=Latte
JSON响应有效载荷:
{
"id": 9,
"name": "Espresso",
"parentId": 8
}
我可以翻译中文。
能否获取特定子级别的节点?
如何使用递归获取所有层级上的节点(我知道这将涉及不同的REST GET调用/ REST终端点)?
需要使用递归来获取所有子级/子层级,但是不知道如何在获取子节点和删除节点时实现。