Java 使用entitymanager的正确方法是什么
Jersey JAX-RS中有一个REST客户机，它接收请求，然后使用Hibernate的JPA实现从数据库检索数据并返回JSON 使用共享实体管理器，性能非常好，但是如果有多个请求，我会从Hibernate获得异常，主要是NullPointerException 如果我对每个请求使用实体管理器，我不会得到任何异常，但性能较低 处理EntityManager的正确方法是什么 编辑： 在下面的Albert评论之后，我使用了 并将entityManager引用更改为使用entityManager.getEntityManager e、 g 到 编辑结束 下面是我使用的代码 Jersey.javaJava 使用entitymanager的正确方法是什么,java,hibernate,jersey,jax-rs,jpa-2.1,Java,Hibernate,Jersey,Jax Rs,Jpa 2.1,Jersey JAX-RS中有一个REST客户机，它接收请求，然后使用Hibernate的JPA实现从数据库检索数据并返回JSON 使用共享实体管理器，性能非常好，但是如果有多个请求，我会从Hibernate获得异常，主要是NullPointerException 如果我对每个请求使用实体管理器，我不会得到任何异常，但性能较低 处理EntityManager的正确方法是什么 编辑： 在下面的Albert评论之后，我使用了 并将entityManager引用更改为使用entityManager.g
package local.domain;
import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.Produces;
import javax.ws.rs.QueryParam;
import javax.ws.rs.core.MediaType;
import javax.ws.rs.core.Response;
@Path("/testJersey")
public class Jersey {
static MainClass mainClass = new MainClass();
@GET
@Produces("application/json")
public Response getAccounts(@QueryParam(value = "userId") final int userId) {
String jsonString = mainClass.getAccounts(userId);
return Response.ok(jsonString, MediaType.APPLICATION_JSON).build();
}// getJson
@Path("/fields/")
@GET
@Produces("application/json")
public Response getAccountFields(@QueryParam(value = "accountId") final int accountId) {
String jsonString = mainClass.getAccountFields(accountId);
return Response.ok(jsonString, MediaType.APPLICATION_JSON).build();
}// getJson
}
package local.domain;
import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import local.domain.pojos.Account;
import local.domain.pojos.User;
public class MainClass {
private EntityManagerFactory entityManagerFactory = null;
private EntityManager entityManager;
boolean sharedEntityManager = true;
public MainClass() {
entityManagerFactory = Persistence.createEntityManagerFactory("peristenceConfig");
entityManager = entityManagerFactory.createEntityManager();
}
public String getAccounts(int userId) {
String result = null;
try {
User reqUser = null;
EntityManager entityManagerLocal = null;
if (sharedEntityManager)
reqUser = entityManager.find(User.class, userId);
else {
entityManagerLocal = entityManagerFactory.createEntityManager();
reqUser = entityManagerLocal.find(User.class, userId);
}
Gson gson = new GsonBuilder().excludeFieldsWithoutExposeAnnotation().create();
result = gson.toJson(reqUser);
if (!sharedEntityManager)
entityManagerLocal.close();
} catch (Exception exp) {
System.err.println("Exception with userId"+userId);
exp.printStackTrace();
}
return result;
}
public String getAccountFields(int accountId) {
String result = null;
try {
Account reqAccount = null;
EntityManager entityManagerLocal = null;
if (sharedEntityManager)
reqAccount = entityManager.find(Account.class, accountId);
else {
entityManagerLocal = entityManagerFactory.createEntityManager();
reqAccount = entityManagerLocal.find(Account.class, accountId);
}
Gson gson = new GsonBuilder().excludeFieldsWithoutExposeAnnotation().create();
result = gson.toJson(reqAccount);
if (!sharedEntityManager)
entityManagerLocal.close();
} catch (Exception exp) {
System.err.println("Exception with accountId"+accountId);
exp.printStackTrace();
}
return result;
}
}
<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.1" xmlns="http://xmlns.jcp.org/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence http://xmlns.jcp.org/xml/ns/persistence/persistence_2_1.xsd">
<persistence-unit name="peristenceConfig">
<class>local.domain.pojos.Account</class>
<class>local.domain.pojos.AccountField</class>
<class>local.domain.pojos.User</class>
<properties>
<property name="hibernate.connection.driver_class" value="com.mysql.jdbc.Driver" />
<property name="hibernate.dialect" value="org.hibernate.dialect.MySQLDialect" />
<property name="hibernate.show_sql" value="true" />
<property name="hibernate.connection.url" value="jdbc:mysql://localhost/jpatest" />
<property name="hibernate.default_schema" value="jpatest" />
<property name="hibernate.connection.username" value="username" />
<property name="hibernate.connection.password" value="password" />
</properties>
</persistence-unit>
</persistence>
<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>Snippet</groupId>
<artifactId>Snippet</artifactId>
<version>0.0.1-SNAPSHOT</version>
<packaging>war</packaging>
<build>
<sourceDirectory>src</sourceDirectory>
<plugins>
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.5.1</version>
<configuration>
<source>1.8</source>
<target>1.8</target>
</configuration>
</plugin>
<plugin>
<artifactId>maven-war-plugin</artifactId>
<version>3.0.0</version>
<configuration>
<warSourceDirectory>WebContent</warSourceDirectory>
</configuration>
</plugin>
</plugins>
</build>
<properties>
<jersey.version>2.26-b02</jersey.version>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
</properties>
<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>
<repositories>
<repository>
<id>JBoss repository</id>
<url>http://repository.jboss.org/nexus/content/groups/public/</url>
</repository>
</repositories>
<dependencies>
<dependency>
<groupId>org.glassfish.jersey.containers</groupId>
<artifactId>jersey-container-servlet-core</artifactId>
</dependency>
<dependency>
<groupId>javax.ws.rs</groupId>
<artifactId>jsr311-api</artifactId>
<version>1.1.1</version>
</dependency>
<dependency>
<groupId>org.hibernate.javax.persistence</groupId>
<artifactId>hibernate-jpa-2.1-api</artifactId>
<version>1.0.0.Final</version>
</dependency>
<dependency>
<groupId>com.google.code.gson</groupId>
<artifactId>gson</artifactId>
<version>2.8.0</version>
</dependency>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>5.1.6</version>
</dependency>
<dependency>
<groupId>org.hibernate</groupId>
<artifactId>hibernate-core</artifactId>
<version>5.2.6.Final</version>
</dependency>
</dependencies>
</project>
package local.domain.pojos;
import java.io.Serializable;
import java.util.List;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.NamedQuery;
import javax.persistence.OneToMany;
import javax.persistence.Table;
import com.google.gson.annotations.Expose;
/**
* The persistent class for the tbl_account database table.
*
*/
@Entity
@Table(name="tbl_account")
@NamedQuery(name="Account.findAll", query="SELECT a FROM Account a")
public class Account implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@Column(name="account_id")
@Expose
@GeneratedValue(strategy = GenerationType.AUTO)
private int accountId;
@Column(name="account_status")
@Expose
private String accountStatus;
//bi-directional many-to-one association to User
@ManyToOne
@JoinColumn(name="user_id")
private User tblUser;
//bi-directional many-to-one association to AccountField
@OneToMany(mappedBy="tblAccount")
@Expose
private List<AccountField> tblAccountFields;
public Account() {
}
public int getAccountId() {
return this.accountId;
}
public void setAccountId(int accountId) {
this.accountId = accountId;
}
public String getAccountStatus() {
return this.accountStatus;
}
public void setAccountStatus(String accountStatus) {
this.accountStatus = accountStatus;
}
public User getTblUser() {
return this.tblUser;
}
public void setTblUser(User tblUser) {
this.tblUser = tblUser;
}
public List<AccountField> getTblAccountFields() {
return this.tblAccountFields;
}
public void setTblAccountFields(List<AccountField> tblAccountFields) {
this.tblAccountFields = tblAccountFields;
}
public AccountField addTblAccountField(AccountField tblAccountField) {
getTblAccountFields().add(tblAccountField);
tblAccountField.setTblAccount(this);
return tblAccountField;
}
public AccountField removeTblAccountField(AccountField tblAccountField) {
getTblAccountFields().remove(tblAccountField);
tblAccountField.setTblAccount(null);
return tblAccountField;
}
}
package local.domain.pojos;
import java.io.Serializable;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.NamedQuery;
import javax.persistence.Table;
import com.google.gson.annotations.Expose;
/**
* The persistent class for the tbl_account_field database table.
*
*/
@Entity
@Table(name="tbl_account_field")
@NamedQuery(name="AccountField.findAll", query="SELECT a FROM AccountField a")
public class AccountField implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@Column(name="account_field_id")
@Expose
@GeneratedValue(strategy = GenerationType.AUTO)
private int accountFieldId;
@Column(name="account_field_label")
@Expose
private String accountFieldLabel;
//bi-directional many-to-one association to Account
@ManyToOne
@JoinColumn(name="account_id")
private Account tblAccount;
public AccountField() {
}
public int getAccountFieldId() {
return this.accountFieldId;
}
public void setAccountFieldId(int accountFieldId) {
this.accountFieldId = accountFieldId;
}
public String getAccountFieldLabel() {
return this.accountFieldLabel;
}
public void setAccountFieldLabel(String accountFieldLabel) {
this.accountFieldLabel = accountFieldLabel;
}
public Account getTblAccount() {
return this.tblAccount;
}
public void setTblAccount(Account tblAccount) {
this.tblAccount = tblAccount;
}
}
package local.domain.pojos;
import java.io.Serializable;
import java.sql.Timestamp;
import java.util.List;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Lob;
import javax.persistence.NamedQuery;
import javax.persistence.OneToMany;
import javax.persistence.Table;
import com.google.gson.annotations.Expose;
/**
* The persistent class for the tbl_user database table.
*
*/
@Entity
@Table(name="tbl_user")
@NamedQuery(name="User.findAll", query="SELECT u FROM User u")
public class User implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@Column(name="user_id")
@Expose
@GeneratedValue(strategy = GenerationType.AUTO)
private int userId;
@Lob
@Column(name="user_email")
@Expose
private String userEmail;
@Column(name="user_last_login")
@Expose
private Timestamp userLastLogin;
@Column(name="user_name")
@Expose
private String userName;
//bi-directional many-to-one association to Account
@OneToMany(mappedBy="tblUser")
@Expose
private List<Account> tblAccounts;
public User() {
}
public int getUserId() {
return this.userId;
}
public void setUserId(int userId) {
this.userId = userId;
}
public String getUserEmail() {
return this.userEmail;
}
public void setUserEmail(String userEmail) {
this.userEmail = userEmail;
}
public Timestamp getUserLastLogin() {
return this.userLastLogin;
}
public void setUserLastLogin(Timestamp userLastLogin) {
this.userLastLogin = userLastLogin;
}
public String getUserName() {
return this.userName;
}
public void setUserName(String userName) {
this.userName = userName;
}
public List<Account> getTblAccounts() {
return this.tblAccounts;
}
public void setTblAccounts(List<Account> tblAccounts) {
this.tblAccounts = tblAccounts;
}
public Account addTblAccount(Account tblAccount) {
getTblAccounts().add(tblAccount);
tblAccount.setTblUser(this);
return tblAccount;
}
public Account removeTblAccount(Account tblAccount) {
getTblAccounts().remove(tblAccount);
tblAccount.setTblUser(null);
return tblAccount;
}
}
正确的方法可能因应用程序类型而异。在您的情况下，我认为共享EntityManager将导致您已经体验到的不想要的行为 我认为每个请求的方法是一种安全的实现方法。另一种可能是对每个线程使用EntityManager，使用ThreadLocal来管理它，Spring就是这样做的。但这可能会使您的实现更加复杂 编辑：每个线程使用EntityManager在使用NIO处理同一线程内的多个请求时可能会导致问题
<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>Snippet</groupId>
<artifactId>Snippet</artifactId>
<version>0.0.1-SNAPSHOT</version>
<packaging>war</packaging>
<build>
<sourceDirectory>src</sourceDirectory>
<plugins>
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.5.1</version>
<configuration>
<source>1.8</source>
<target>1.8</target>
</configuration>
</plugin>
<plugin>
<artifactId>maven-war-plugin</artifactId>
<version>3.0.0</version>
<configuration>
<warSourceDirectory>WebContent</warSourceDirectory>
</configuration>
</plugin>
</plugins>
</build>
<properties>
<jersey.version>2.26-b02</jersey.version>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
</properties>
<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>
<repositories>
<repository>
<id>JBoss repository</id>
<url>http://repository.jboss.org/nexus/content/groups/public/</url>
</repository>
</repositories>
<dependencies>
<dependency>
<groupId>org.glassfish.jersey.containers</groupId>
<artifactId>jersey-container-servlet-core</artifactId>
</dependency>
<dependency>
<groupId>javax.ws.rs</groupId>
<artifactId>jsr311-api</artifactId>
<version>1.1.1</version>
</dependency>
<dependency>
<groupId>org.hibernate.javax.persistence</groupId>
<artifactId>hibernate-jpa-2.1-api</artifactId>
<version>1.0.0.Final</version>
</dependency>
<dependency>
<groupId>com.google.code.gson</groupId>
<artifactId>gson</artifactId>
<version>2.8.0</version>
</dependency>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>5.1.6</version>
</dependency>
<dependency>
<groupId>org.hibernate</groupId>
<artifactId>hibernate-core</artifactId>
<version>5.2.6.Final</version>
</dependency>
</dependencies>
</project>
package local.domain.pojos;
import java.io.Serializable;
import java.util.List;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.NamedQuery;
import javax.persistence.OneToMany;
import javax.persistence.Table;
import com.google.gson.annotations.Expose;
/**
* The persistent class for the tbl_account database table.
*
*/
@Entity
@Table(name="tbl_account")
@NamedQuery(name="Account.findAll", query="SELECT a FROM Account a")
public class Account implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@Column(name="account_id")
@Expose
@GeneratedValue(strategy = GenerationType.AUTO)
private int accountId;
@Column(name="account_status")
@Expose
private String accountStatus;
//bi-directional many-to-one association to User
@ManyToOne
@JoinColumn(name="user_id")
private User tblUser;
//bi-directional many-to-one association to AccountField
@OneToMany(mappedBy="tblAccount")
@Expose
private List<AccountField> tblAccountFields;
public Account() {
}
public int getAccountId() {
return this.accountId;
}
public void setAccountId(int accountId) {
this.accountId = accountId;
}
public String getAccountStatus() {
return this.accountStatus;
}
public void setAccountStatus(String accountStatus) {
this.accountStatus = accountStatus;
}
public User getTblUser() {
return this.tblUser;
}
public void setTblUser(User tblUser) {
this.tblUser = tblUser;
}
public List<AccountField> getTblAccountFields() {
return this.tblAccountFields;
}
public void setTblAccountFields(List<AccountField> tblAccountFields) {
this.tblAccountFields = tblAccountFields;
}
public AccountField addTblAccountField(AccountField tblAccountField) {
getTblAccountFields().add(tblAccountField);
tblAccountField.setTblAccount(this);
return tblAccountField;
}
public AccountField removeTblAccountField(AccountField tblAccountField) {
getTblAccountFields().remove(tblAccountField);
tblAccountField.setTblAccount(null);
return tblAccountField;
}
}
package local.domain.pojos;
import java.io.Serializable;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.NamedQuery;
import javax.persistence.Table;
import com.google.gson.annotations.Expose;
/**
* The persistent class for the tbl_account_field database table.
*
*/
@Entity
@Table(name="tbl_account_field")
@NamedQuery(name="AccountField.findAll", query="SELECT a FROM AccountField a")
public class AccountField implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@Column(name="account_field_id")
@Expose
@GeneratedValue(strategy = GenerationType.AUTO)
private int accountFieldId;
@Column(name="account_field_label")
@Expose
private String accountFieldLabel;
//bi-directional many-to-one association to Account
@ManyToOne
@JoinColumn(name="account_id")
private Account tblAccount;
public AccountField() {
}
public int getAccountFieldId() {
return this.accountFieldId;
}
public void setAccountFieldId(int accountFieldId) {
this.accountFieldId = accountFieldId;
}
public String getAccountFieldLabel() {
return this.accountFieldLabel;
}
public void setAccountFieldLabel(String accountFieldLabel) {
this.accountFieldLabel = accountFieldLabel;
}
public Account getTblAccount() {
return this.tblAccount;
}
public void setTblAccount(Account tblAccount) {
this.tblAccount = tblAccount;
}
}
package local.domain.pojos;
import java.io.Serializable;
import java.sql.Timestamp;
import java.util.List;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Lob;
import javax.persistence.NamedQuery;
import javax.persistence.OneToMany;
import javax.persistence.Table;
import com.google.gson.annotations.Expose;
/**
* The persistent class for the tbl_user database table.
*
*/
@Entity
@Table(name="tbl_user")
@NamedQuery(name="User.findAll", query="SELECT u FROM User u")
public class User implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@Column(name="user_id")
@Expose
@GeneratedValue(strategy = GenerationType.AUTO)
private int userId;
@Lob
@Column(name="user_email")
@Expose
private String userEmail;
@Column(name="user_last_login")
@Expose
private Timestamp userLastLogin;
@Column(name="user_name")
@Expose
private String userName;
//bi-directional many-to-one association to Account
@OneToMany(mappedBy="tblUser")
@Expose
private List<Account> tblAccounts;
public User() {
}
public int getUserId() {
return this.userId;
}
public void setUserId(int userId) {
this.userId = userId;
}
public String getUserEmail() {
return this.userEmail;
}
public void setUserEmail(String userEmail) {
this.userEmail = userEmail;
}
public Timestamp getUserLastLogin() {
return this.userLastLogin;
}
public void setUserLastLogin(Timestamp userLastLogin) {
this.userLastLogin = userLastLogin;
}
public String getUserName() {
return this.userName;
}
public void setUserName(String userName) {
this.userName = userName;
}
public List<Account> getTblAccounts() {
return this.tblAccounts;
}
public void setTblAccounts(List<Account> tblAccounts) {
this.tblAccounts = tblAccounts;
}
public Account addTblAccount(Account tblAccount) {
getTblAccounts().add(tblAccount);
tblAccount.setTblUser(this);
return tblAccount;
}
public Account removeTblAccount(Account tblAccount) {
getTblAccounts().remove(tblAccount);
tblAccount.setTblUser(null);
return tblAccount;
}
}