Spring Boot構建RESTful Web服務

Spring Boot為為企業應用程式構建RESTful Web服務提供了非常好的支持。本章將詳細介紹如何使用Spring Boot構建RESTful Web服務。

注 - 要構建RESTful Web服務，需要將Spring Boot Starter Web依賴項添加到構建配置檔中。

如果是Maven用戶，請使用以下代碼在pom.xml 檔中添加以下依賴項 -

<dependency>
   <groupId>org.springframework.boot</groupId>
   <artifactId>spring-boot-starter-web</artifactId>
</dependency>

如果是Gradle用戶，請使用以下代碼在build.gradle 檔中添加以下依賴項。

compile('org.springframework.boot:spring-boot-starter-web')

完整的構建配置檔Maven build - pom.xml 的代碼如下 -

<?xml version = "1.0" encoding = "UTF-8"?>
<project xmlns = "http://maven.apache.org/POM/4.0.0"
   xmlns:xsi = "http://www.w3.org/2001/XMLSchema-instance"
   xsi:schemaLocation = "http://maven.apache.org/POM/4.0.0
   http://maven.apache.org/xsd/maven-4.0.0.xsd">

   <modelVersion>4.0.0</modelVersion>
   <groupId>com.zaixian</groupId>
   <artifactId>demo</artifactId>
   <version>0.0.1-SNAPSHOT</version>
   <packaging>jar</packaging>
   <name>demo</name>
   <description>Demo project for Spring Boot</description>

   <parent>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-parent</artifactId>
      <version>1.5.8.RELEASE</version>
      <relativePath/>
   </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>
   </dependencies>

   <build>
      <plugins>
         <plugin>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-maven-plugin</artifactId>
         </plugin>
      </plugins>
   </build>

</project>

完整的構建配置檔Gradle Build - build.gradle 的代碼如下 -

buildscript {
   ext {
      springBootVersion = '1.5.8.RELEASE'
   }
   repositories {
      mavenCentral()
   }
   dependencies {
      classpath("org.springframework.boot:spring-boot-gradle-plugin:${springBootVersion}")
   }
}

apply plugin: 'java'
apply plugin: 'eclipse'
apply plugin: 'org.springframework.boot'

group = 'com.zaixian'
version = '0.0.1-SNAPSHOT'
sourceCompatibility = 1.8

repositories {
   mavenCentral()
}
dependencies {
   compile('org.springframework.boot:spring-boot-starter-web')
   testCompile('org.springframework.boot:spring-boot-starter-test')
}

在繼續構建RESTful Web服務之前，建議瞭解以下注釋 -

Rest控制器

@RestController注釋用於定義RESTful Web服務。它提供JSON，XML和自定義回應。其語法如下所示 -

@RestController
public class ProductServiceController {
}

請求映射

@RequestMapping注釋用於定義訪問REST端點的Request URI。可以定義Request方法來使用和生成對象。默認請求方法是:GET。

@RequestMapping(value = "/products")
public ResponseEntity<Object> getProducts() { }

請求主體

@RequestBody注釋用於定義請求正文內容類型。

public ResponseEntity<Object> createProduct(@RequestBody Product product) {
}

路徑變數

@PathVariable批註用於定義自定義或動態請求URI。請求URI中的Path變數定義為花括弧{}，如下所示 -

public ResponseEntity<Object> updateProduct(@PathVariable("id") String id) {
}

請求參數

@RequestParam注釋用於從請求URL讀取請求參數。默認情況下，它是必需參數。還可以為請求參數設置默認值，如下所示 -

public ResponseEntity<Object> getProduct(
   @RequestParam(value = "name", required = false, defaultValue = "honey") String name) {
}

GET API

默認的HTTP請求方法是GET。此方法不需要任何請求主體。可以發送請求參數和路徑變數來自定義或動態URL。
用於定義HTTP GET請求方法的示例代碼如下所示。在此示例中使用HashMap存儲產品。請注意，使用POJO類作為要存儲的產品。
這裏，請求URI是/products，它將從HashMap存儲庫返回產品列表。下麵給出了包含GET方法REST端點的控制器類檔。

package com.zaixian.demo.controller;

import java.util.HashMap;
import java.util.Map;

import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import com.zaixian.demo.model.Product;

@RestController
public class ProductServiceController {
   private static Map<String, Product> productRepo = new HashMap<>();
   static {
      Product honey = new Product();
      honey.setId("1");
      honey.setName("Honey");
      productRepo.put(honey.getId(), honey);

      Product almond = new Product();
      almond.setId("2");
      almond.setName("Almond");
      productRepo.put(almond.getId(), almond);
   }
   @RequestMapping(value = "/products")
   public ResponseEntity<Object> getProduct() {
      return new ResponseEntity<>(productRepo.values(), HttpStatus.OK);
   }
}

POST API

HTTP POST請求用於創建資源。此方法包含請求正文。可以發送請求參數和路徑變數來定義自定義或動態URL。
以下示例顯示了用於定義HTTP POST請求方法的示例代碼。在此示例中，使用HashMap存儲Product，其中產品是POJO類。
這裏，請求URI是/products，它會在將產品存儲到HashMap存儲庫後返回字串。

package com.zaixian.demo.controller;

import java.util.HashMap;
import java.util.Map;

import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;

import com.zaixian.demo.model.Product;

@RestController
public class ProductServiceController {
   private static Map<String, Product> productRepo = new HashMap<>();

   @RequestMapping(value = "/products", method = RequestMethod.POST)
   public ResponseEntity<Object> createProduct(@RequestBody Product product) {
      productRepo.put(product.getId(), product);
      return new ResponseEntity<>("Product is created successfully", HttpStatus.CREATED);
   }
}

PUT API

HTTP PUT請求用於更新現有資源，此方法包含請求正文。可以發送請求參數和路徑變數來自定義或動態URL。
下麵給出的示例顯示了如何定義HTTP PUT請求方法。在此示例中使用HashMap更新現有產品，其中產品是POJO類。
這裏的請求URI是/products/{id}，它將產品存儲到HashMap庫後返回String。請注意，使用路徑變數{id}來定義需要更新的產品ID。

package com.zaixian.demo.controller;

import java.util.HashMap;
import java.util.Map;

import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;
import com.zaixian.demo.model.Product;

@RestController
public class ProductServiceController {
   private static Map<String, Product> productRepo = new HashMap<>();

   @RequestMapping(value = "/products/{id}", method = RequestMethod.PUT)
   public ResponseEntity<Object> updateProduct(@PathVariable("id") String id, @RequestBody Product product) {
      productRepo.remove(id);
      product.setId(id);
      productRepo.put(id, product);
      return new ResponseEntity<>("Product is updated successsfully", HttpStatus.OK);
   }
}

DELETE API

HTTP刪除請求用於刪除現有資源。此方法不包含任何請求正文。可以發送請求參數和路徑變數來自定義或動態URL。
下麵給出的示例顯示了如何定義HTTP DELETE請求方法。在此示例中，使用HashMap刪除現有產品，即POJO類。
請求URI是/products/{id}，它將在從HashMap存儲庫中刪除產品後返回字串。使用路徑變數{id}來定義需要刪除的產品ID。

package com.zaixian.demo.controller;

import java.util.HashMap;
import java.util.Map;

import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;

import com.zaixian.demo.model.Product;

@RestController
public class ProductServiceController {
   private static Map<String, Product> productRepo = new HashMap<>();

   @RequestMapping(value = "/products/{id}", method = RequestMethod.DELETE)
   public ResponseEntity<Object> delete(@PathVariable("id") String id) {
      productRepo.remove(id);
      return new ResponseEntity<>("Product is deleted successsfully", HttpStatus.OK);
   }
}

本節提供完整的源代碼集。請遵守以下代碼瞭解其各自的功能 -

Spring Boot主應用程式類 - DemoApplication.java :

package com.zaixian.demo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class DemoApplication {
   public static void main(String[] args) {
      SpringApplication.run(DemoApplication.class, args);
   }
}

POJO類 - Product.java

package com.zaixian.demo.model;

public class Product {
   private String id;
   private String name;

   public String getId() {
      return id;
   }
   public void setId(String id) {
      this.id = id;
   }
   public String getName() {
      return name;
   }
   public void setName(String name) {
      this.name = name;
   }
}

Rest Controller類 - ProductServiceController.java

package com.zaixian.demo.controller;

import java.util.HashMap;
import java.util.Map;

import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;

import com.zaixian.demo.model.Product;

@RestController
public class ProductServiceController {
   private static Map<String, Product> productRepo = new HashMap<>();
   static {
      Product honey = new Product();
      honey.setId("1");
      honey.setName("Honey");
      productRepo.put(honey.getId(), honey);

      Product almond = new Product();
      almond.setId("2");
      almond.setName("Almond");
      productRepo.put(almond.getId(), almond);
   }

   @RequestMapping(value = "/products/{id}", method = RequestMethod.DELETE)
   public ResponseEntity<Object> delete(@PathVariable("id") String id) {
      productRepo.remove(id);
      return new ResponseEntity<>("Product is deleted successsfully", HttpStatus.OK);
   }

   @RequestMapping(value = "/products/{id}", method = RequestMethod.PUT)
   public ResponseEntity<Object> updateProduct(@PathVariable("id") String id, @RequestBody Product product) {
      productRepo.remove(id);
      product.setId(id);
      productRepo.put(id, product);
      return new ResponseEntity<>("Product is updated successsfully", HttpStatus.OK);
   }

   @RequestMapping(value = "/products", method = RequestMethod.POST)
   public ResponseEntity<Object> createProduct(@RequestBody Product product) {
      productRepo.put(product.getId(), product);
      return new ResponseEntity<>("Product is created successfully", HttpStatus.CREATED);
   }

   @RequestMapping(value = "/products")
   public ResponseEntity<Object> getProduct() {
      return new ResponseEntity<>(productRepo.values(), HttpStatus.OK);
   }
}

可以創建一個可執行的JAR檔，並使用下麵的Maven或Gradle命令運行spring boot應用程式。
對於Maven，請使用下麵顯示的命令 -