获取空指针异常实现 JAX_RS

Question

我是 JAX-RS 的新手。我正在使用 JAX_RS 进行 CRUD 操作。 CRUD 操作对于 JSF 工作正常，但是当我使用 JAX-RS 调用服务层中存在的 fetchAll() 方法时，我得到一个 NullPointerException。

下面是我的JAX_RS代码

package com.resource;

import java.util.List;

import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.Produces;
import javax.ws.rs.core.MediaType;

import com.neorays.resource.entity.Person;
import com.neorays.resource.service.PersonService;

@Path("/persons")
public class MyResource {

    PersonService ser = new PersonService();

    @GET
    @Path("/pers")
    @Produces(MediaType.APPLICATION_JSON)
    public List<Person> getAllPerson() {
        List<Person> list = null;
        try {
            list = ser.fetchAll();
            for (Person person : list) {
                person.getId();
                System.out.println("person id is" + person.getId());
                System.out.println("person name is" + person.getName());
                System.out.println("person country is" + person.getCountry());

            }
        } catch (NullPointerException ne) {
            System.out.println("null pt is occuring" + ne);
        }
        return list;
    }

}

这是我的服务层

package com.resource.service;

import java.util.List;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;

import com.neorays.resource.bean.PersonBean;
import com.neorays.resource.dao.PersonDao;
import com.neorays.resource.entity.Person;

@Component
@Transactional
public class PersonService 
{
    @Autowired
    private PersonDao dao;

    @Transactional
    public List<Person> fetchAll()
    {
        return dao.fetchAll();
    }
}

这是我的 DAO 层

package com.resource.dao;

import java.util.List;

import org.hibernate.Query;
import org.hibernate.SessionFactory;
import org.hibernate.classic.Session;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Repository;

import com.neorays.resource.bean.PersonBean;
import com.neorays.resource.entity.Person;

@Repository
public class PersonDao 
{
    @Autowired
   private SessionFactory sessionFactory;

    public List<Person> fetchAll()
    {
        Session ses = sessionFactory.getCurrentSession();
        String query="from Person";
        Query query2 =ses.createQuery(query);
        List<Person> list = query2.list();

        return list;
    }
}

这是我的web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns="http://java.sun.com/xml/ns/javaee"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
    version="2.5">


    <!-- needed for ContextLoaderListener -->
    <context-param>
        <param-name>contextConfigLocation</param-name>
        <param-value>classpath:applicationContext.xml</param-value>
    </context-param>

    <!-- Bootstraps the root web application context before servlet initialization -->
    <listener>
        <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
    </listener>

    <servlet>
        <servlet-name>Faces Servlet</servlet-name>
        <servlet-class>javax.faces.webapp.FacesServlet</servlet-class>
        <load-on-startup>1</load-on-startup>
    </servlet>
    <servlet-mapping>
        <servlet-name>Faces Servlet</servlet-name>
        <url-pattern>/faces/*</url-pattern>
    </servlet-mapping>

    <servlet>
        <servlet-name>Jersey Web Application</servlet-name>
        <servlet-class>org.glassfish.jersey.servlet.ServletContainer</servlet-class>
        <init-param>
            <param-name>jersey.config.server.provider.packages</param-name>
            <param-value>com.neorays.resource</param-value>
        </init-param>
        <load-on-startup>1</load-on-startup>
    </servlet>
    <servlet-mapping>
        <servlet-name>Jersey Web Application</servlet-name>
        <url-pattern>/webapi/*</url-pattern>
    </servlet-mapping>
</web-app>

这是我的pom.xml

<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.resource</groupId>
    <artifactId>jsf_jaxrs</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>war</packaging>

    <build>
        <finalName>jsf_jaxrs</finalName>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>2.5.1</version>
                <inherited>true</inherited>
                <configuration>
                    <source>1.7</source>
                    <target>1.7</target>
                </configuration>
            </plugin>
        </plugins>
      </build>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.glassfish.jersey</groupId>
                <artifactId>jersey-bom</artifactId>
                <version>${jersey.version}</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>

    <dependencies>
        <dependency>
            <groupId>org.glassfish.jersey.containers</groupId>
            <artifactId>jersey-container-servlet-core</artifactId>
            <!-- use the following artifactId if you don't need servlet 2.x compatibility -->
            <!-- artifactId>jersey-container-servlet</artifactId -->
        </dependency>
        <!-- uncomment this to get JSON support  -->
        <dependency>
            <groupId>org.glassfish.jersey.media</groupId>
            <artifactId>jersey-media-moxy</artifactId>
        </dependency>

     <dependency>
    <groupId>org.hibernate</groupId>
    <artifactId>hibernate-core</artifactId>
    <version>3.6.10.Final</version>
</dependency>

    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>5.1.26</version>
    </dependency>
    <dependency>
        <groupId>javassist</groupId>
        <artifactId>javassist</artifactId>
        <version>3.12.1.GA</version>
    </dependency>
    <dependency>
        <groupId>commons-dbcp</groupId>
        <artifactId>commons-dbcp</artifactId>
        <version>1.2.1</version>
    </dependency>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-orm</artifactId>
        <version>3.2.10.RELEASE</version>
    </dependency>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-web</artifactId>
        <version>3.2.10.RELEASE</version>
    </dependency>
    <dependency>
        <groupId>org.glassfish</groupId>
        <artifactId>javax.faces</artifactId>
        <version>2.2.4</version>
    </dependency>
    <dependency>
        <groupId>javax.el</groupId>
        <artifactId>el-api</artifactId>
        <version>2.2</version>
    </dependency>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-context</artifactId>
        <version>3.2.10.RELEASE</version>
    </dependency>
    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>4.11</version>
    </dependency>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-beans</artifactId>
        <version>3.2.10.RELEASE</version>
    </dependency>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-test</artifactId>
        <version>3.2.4.RELEASE</version>
    </dependency>
    <dependency>
        <groupId>org.hibernate</groupId>
        <artifactId>hibernate-validator</artifactId>
        <version>4.2.0.Final</version>
    </dependency>

    <dependency>
        <groupId>jstl</groupId>
        <artifactId>jstl</artifactId>
        <version>1.2</version>
    </dependency>
    </dependencies>

    <properties>
        <jersey.version>2.16</jersey.version>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    </properties>
</project>

最后，这是我的 Bean

package com.neorays.resource.entity;

import java.io.Serializable;

import javax.persistence.*;
import javax.xml.bind.annotation.XmlRootElement;

@XmlRootElement
@Entity
@NamedQuery(name="Person.findAll", query="SELECT p FROM Person p")
public class Person implements Serializable {
    private static final long serialVersionUID = 1L;
    private int id;
    private String country;
    private String name;

    public Person() {
    }
    public Person(int id, String country, String name) {
        super();
        this.id = id;
        this.country = country;
        this.name = name;
    }
    @Id
    public int getId() {
        return this.id;
    }

    public void setId(int id) {
        this.id = id;
    }


    public String getCountry() {
        return this.country;
    }

    public void setCountry(String country) {
        this.country = country;
    }
    public String getName() {
        return this.name;
    }

    public void setName(String name) {
        this.name = name;
    }

}

Answer 1

您的依赖注入构造不正确。您的所有 bean 都必须由 Spring 创建。如果您的 applicationContext.xml 文件扫描必要的包（至少对于服务和 daos），并且如果您的 hibernate 会话工厂创建正确并且因为您已经告诉 jersey 扫描包以获取其余服务，这应该可以工作。

@Component
@Path("/persons")
public class MyResource {

    @Autowired
    PersonService ser;
    ...

}

更新

我才发现web.xml里面的包名和你们其他的服务不一样

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns="http://java.sun.com/xml/ns/javaee"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
    version="2.5">
    ....

    <servlet>
        <servlet-name>Jersey Web Application</servlet-name>
        <servlet-class>org.glassfish.jersey.servlet.ServletContainer</servlet-class>
        <init-param>
            <param-name>jersey.config.server.provider.packages</param-name>
            <param-value>com.resource</param-value>
        </init-param>
        <load-on-startup>1</load-on-startup>
    </servlet>
    <servlet-mapping>
        <servlet-name>Jersey Web Application</servlet-name>
        <url-pattern>/webapi/*</url-pattern>
    </servlet-mapping>
    ....
</web-app>

如果您的 class 路径中缺少 jersey-spring3，您可以使用 maven 添加它。

<dependency>
    <groupId>org.glassfish.jersey.ext</groupId>
    <artifactId>jersey-spring3</artifactId>
    <version>${jersey.version}</version>
</dependency>

您可以在 jersey documentation 上找到更多信息。

获取空指针异常实现 JAX_RS

Getting Null Pointer Exception implementing JAX_RS

spring

hibernate

jax-rs

jersey-2.0

更新