Spring Boot无法返回对象的JSON，但不返回对象列表

Question

我正在开发我的第一个Spring Boot应用程序，我遇到了一个奇怪的问题。 配置非常基础：

    <?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.pawsec</groupId>
    <artifactId>kitchen</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>kitchen</name>
    <description>The Kitchen restaurant system</description>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.1.0.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </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-aop</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-jdbc</artifactId>
        </dependency> 
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>com.pawsec</groupId>
            <artifactId>common</artifactId>
            <version>1.0</version>
        </dependency>
    </dependencies>

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


</project>

我们在调用这两个服务的页面上有一些Javascript代码。 当控制器在第一个方法中返回Guy对象时，我们得到一个空响应：

    {data: "", status: 200, statusText: "", headers: {…}, config: {…}, …}
config: {adapter: ƒ, transformRequest: {…}, transformResponse: {…}, timeout: 0, xsrfCookieName: "XSRF-TOKEN", …}
data: ""
headers: {}
request: XMLHttpRequest {onreadystatechange: ƒ, readyState: 4, timeout: 0, withCredentials: false, upload: XMLHttpRequestUpload, …}
status: 200
statusText: ""
: Object

但是，当我们从第二种方法返回一个Guy对象列表时，我们得到了完整的Json结构

back:
{data: Array(3), status: 200, statusText: "", headers: {…}, config: {…}, …}
config: {adapter: ƒ, transformRequest: {…}, transformResponse: {…}, timeout: 0, xsrfCookieName: "XSRF-TOKEN", …}
data: Array(3)
0: {guyId: 1, name: "Walter Sobchak", age: 45}
1: {guyId: 2, name: "Jeffrey Lebowski", age: 42}
2: {guyId: 3, name: "Theodore Donald Kerabatsos", age: 39}
length: 3
: Array(0)
headers: {content-type: "application/json;charset=UTF-8", cache-control: "private", expires: "Thu, 01 Jan 1970 00:00:00 GMT"}
request: XMLHttpRequest {onreadystatechange: ƒ, readyState: 4, timeout: 0, withCredentials: false, upload: XMLHttpRequestUpload, …}
status: 200
statusText: ""
: Object

控制器看起来像这样：

package com.pawsec.kitchen.controller;

import java.util.ArrayList;
import java.util.List;

import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;

import com.pawsec.kitchen.model.Guy;

@RestController
public class GuyController {

    @RequestMapping(value="/get/guy/{guyId}", method=RequestMethod.GET,
            headers={"Accept=application/json"})
    public Guy getGuy(@PathVariable("guyId") int guyId) {
        Guy someGuy = new Guy(guyId, "Walter Sobchak", 45);
        return someGuy;
    }

    @RequestMapping(value="/get/guys", method=RequestMethod.GET,
            headers={"Accept=application/json"})
    public List<Guy> getGuys() {
        Guy walter = new Guy(1, "Walter Sobchak", 45);
        Guy theDude = new Guy(2, "Jeffrey Lebowski", 42);
        Guy donny = new Guy(3, "Theodore Donald Kerabatsos", 39);
        List<Guy> guys = new ArrayList<Guy>();
        guys.add(walter);
        guys.add(theDude);
        guys.add(donny);
        return guys;
    }

}

奇怪的是，如果我从浏览器调用这两个服务，我会为这两个调用获得正确的Json结构。

当我运行mvn依赖：树时，基本的Boot Project附带的预期Jackson依赖项就在那里。

这就是JavaScript代码的样子：

return dispatch => {
        dispatch(fetchMenuStart());
        const url = 'https://boot.ourcompany.com:8443/get/guy/1'; 
        const headers = {
            headers: {
                'Content-Type': 'application/json'
            }
        }
        axios.get(url, headers)
            .then(res => {
                console.log(res); 
                dispatch(fetchMenuSuccess(res.data.categories, res.data.restaurant));
            })
            .catch(error => {   
                console.log("error", error);
                const errorMsg = 'There was an error fetching the menu';
                dispatch(fetchMenuFail(errorMsg)); 
            });
    };

任何人都可以建议可能导致此问题或步骤测试以找出问题吗？

新的javascript示例代码：

const doesNotWork = 'https://boot.exmpledomain.com:8443/get/guy/1'; 
const doesWork = 'https://boot.exmpledomain.com:8443/get/guys'; 
const headers = {
    headers: {
    'Content-Type': 'application/json;charset=UTF-8'
    }
}
axios.get(doesNotWork, headers)
    .then(res => {
        console.log(res); 
    })
    .catch(error => {   
        console.log("error", error);
        const errorMsg = 'There was an error fetching the menu';
    });

Answer 1

你可以尝试在javascript中更改标题以接受

return dispatch => {
        dispatch(fetchMenuStart());
        const url = 'https://boot.ourcompany.com:8443/get/guy/1'; 
        const headers = {
            headers: {
                'Content-Type': 'application/json',
                'Accept': 'application/json'
            }
        }
        axios.get(url, headers)
            .then(res => {
                console.log(res); 
                dispatch(fetchMenuSuccess(res.data.categories, res.data.restaurant));
            })
            .catch(error => {   
                console.log("error", error);
                const errorMsg = 'There was an error fetching the menu';
                dispatch(fetchMenuFail(errorMsg)); 
            });
    };

Answer 2

我终于通过使用以下类禁用CORS解决了这个问题：

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Profile;
import org.springframework.web.servlet.config.annotation.CorsRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;

@Profile("devel")
@Configuration
public class WebConfig {

    @Bean
    public WebMvcConfigurer corsConfigurer() {
        return new WebMvcConfigurer() {
            @Override
            public void addCorsMappings(CorsRegistry registry) {
                registry.addMapping("/**");
            }
        };
    }

}

我还添加了@Profile注释，仅在开发时禁用CORS。

顺便说一下，问题的原因似乎在下面解释：

https://chromium.googlesource.com/chromium/src/+/master/services/network/cross_origin_read_blocking_explainer.md#Protecting-JSON

返回对象时，它被解释为非空的JSON对象（例如{"key": "value"} ）。 返回列表时，相同的文本用方括号括起来并通过保护 。

Answer 3

由于您的javascript与spring-boot服务位于不同的域，因此您需要配置CORS 。

这可以在全球范围内添加@CrossOrigin如下所示：

@RestController
@CrossOrigin
public class GuyController {

Answer 4

如果使用spring，则应使用ResponseEntity而不是直接返回对象：

import org.springframework.http.HttpStatus;
import org.springframework.http.MediaType;
import org.springframework.http.ResponseEntity;

这就是我编写控制器的方式：

@RestController
@RequestMapping(USERS)
public class UserController {

  @Autowired
  private UserService userService;

  @Autowired
  private RoleService roleService;

  @Autowired
  private LdapUserDetailsManager userDetailsService;

  @GetMapping(produces = MediaType.APPLICATION_JSON_VALUE)
  public ResponseEntity<?> list(PagedResourcesAssembler<User> pageAssembler, @PageableDefault(size = 20) Pageable pageable, UserDTO condition) {
    Page<User> page = userService.findAll(pageable, condition);
    PagedResources<?> resources = pageAssembler.toResource(page, new UserResourceAssembler());
    return ResponseEntity.ok(resources);
  }

  @GetMapping(value = CoreHttpPathStore.PARAM_ID, produces= MediaType.APPLICATION_JSON_VALUE)
  public ResponseEntity<UserResource> get(@PathVariable("id") Long id) {
    User user = userService.get(id);
    UserResource resource = new UserResourceAssembler().toResource(user);
    return ResponseEntity.ok(resource);
  }

  private void preProcessEntity(@RequestBody UserDTO entity) {
    if (null != entity.getPassword()) {
      userDetailsService.changePassword(entity.getOldPassword(), entity.getPassword());
    }
  }

  @PostMapping
  @ResponseStatus(HttpStatus.CREATED)
  Long create(@RequestBody User user) {
    userService.insert(user);
    return user.getId();
  }

  @PutMapping(CoreHttpPathStore.PARAM_ID)
  @ResponseStatus(HttpStatus.NO_CONTENT)
  void modify(@PathVariable("id") Long id, @RequestBody UserDTO user) {
    user.setId(id);
    preProcessEntity(user);
    userService.updateIgnore(user);
  }

  @DeleteMapping(CoreHttpPathStore.PARAM_ID)
  @ResponseStatus(HttpStatus.NO_CONTENT)
  void delete(@PathVariable("id") Long id) {
    userService.delete(id);
  }

  @DeleteMapping
  @ResponseStatus(HttpStatus.NO_CONTENT)
  void bulkDelete(@RequestBody Long[] ids) {
    userService.delete(ids);
  }
}

Answer 5

好的，非常感谢你的努力。 事实证明@mpromonet建议的解决方案（在控制器上添加CrossOrigin注释）解决了这个问题。 我仍然很好奇知道为什么返回List的方法有效，而如果这是一个跨源问题，那么返回Guy的方法就不会。 它似乎不合逻辑，这使得问题更难以弄清楚。

Answer 6

您必须在方法之前添加@ResponseBody注释。

@ResponseBody
public Guy ....