java - Spring Boot中无法加载资源: the server responded with a status of 404. Whitelabel错误页面

Question

I am using spring boot for my application when I run it it show me an error This application has no explicit mapping for /error, so you are seeing this as a fallback.

Sat Jun 06 11:44:29 IST 2020 There was an unexpected error (type=Not Found, status=404). No message available I use my sql for database and sql youg for database editor but it is not able to connect with database

pom.xml

<?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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.0.1.RELEASE</version>
        <relativePath /> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.material</groupId>
    <artifactId>MaterialComp</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>MaterialComp</name>
    <description>Demo project for Spring Boot</description>

    <properties>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>

        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.18</version>
        </dependency>

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

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
            <scope>runtime</scope>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
            <exclusions>
                <exclusion>
                    <groupId>org.junit.vintage</groupId>
                    <artifactId>junit-vintage-engine</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
    </dependencies>

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

</project>

UserEntity.java

package com.material.Entity;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;

@Entity
@Table(name="userentity")
public class UserEntity {
    @Id
    @Column(name="id")
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    private Long id;
    @Column(name="name")
    private String name;

    @Column(name="password")
    private String password;

    @Column(name="type")
    private String type;
    public Long getId() {
        return id;
    }
    public void setId(Long id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }
    public String getType() {
        return type;
    }
    public void setType(String type) {
        this.type = type;
    }


}

UserRepo.java

package com.material.Repo;

import org.springframework.data.jpa.repository.JpaRepository;

import com.material.Entity.UserEntity;

public interface UserRepository extends JpaRepository<UserEntity, Long>{

}

controller.java

package com.material.Controller;

import java.util.List;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.CrossOrigin;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import com.material.Entity.UserEntity;
import com.material.Repo.UserRepository;
@RestController
@CrossOrigin(origins= "http://localhost:4200")
@RequestMapping(path="user")
public class UserController {

    @Autowired
    private UserRepository userRepo;

    @GetMapping("/get")
    public List<UserEntity> getUsers(){
        return userRepo.findAll();

    }
}

application.properties

spring.datasource.url=jdbc:mysql://localhost/ecommerce
spring.datasource.username=root
spring.datasource.password=
spring.jpa.hibernate.ddl-auto=create-drop
spring.jpa.hibernate.use-new-id-generator-mappings=false

Answer 1

这里有一些棘手的事情。

首先，您已将服务器配置为监听 localhost:4200，这很好。您已经用这一行完成了这一点:

@CrossOrigin(origins= "http://localhost:4200")

接下来你告诉了 spring:

@RequestMapping(path="user")

Spring 将获取 user 并将其添加到 http://localhost:4200。所以它现在正在监听 http://localhost:4200user - 这不是您想要的，请尝试添加 / 以便您的请求映射如下所示:

@RequestMapping(path="/user")

您的应用程序现在应该正在监听 http://localhost:4200/user 。太棒了!

接下来，要调用 getUsers 方法，您已经定义了 @GetMapping("/get")，它与其他注释结合起来意味着要调用 getUsers，您需要进行 GET 操作http://localhost:4200/user/get，假设一切正常。

一个小技巧是，@GetMapping 实际上是 @RequestMapping(method = RequestMethod.GET) 的别名 - 因此要整理它，您可以删除 @RequestMapping(path="user") 并使用

@GetMapping(value = "/users") 这意味着针对 http://localhost:4200/user 的 GET 将激活您的 getUsers 方法。