Update 28.3.1. Entity Classes.md

IV. Spring Boot features/28.3.1. Entity Classes.md

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+### 28.3.1. 实体类
+
+传统上，JPA实体类被定义到一个persistence.xml文件中。在Spring Boot中，这个文件不是必需的，并被'实体扫描'替代。默认情况下，在你主（main）配置类（被@EnableAutoConfiguration或@SpringBootApplication注解的类）下的所有包都将被查找。
+
+任何被@Entity，@Embeddable或@MappedSuperclass注解的类都将被考虑。一个普通的实体类看起来像下面这样：
+```java
+package com.example.myapp.domain;
+
+import java.io.Serializable;
+import javax.persistence.*;
+
+@Entity
+public class City implements Serializable {
+
+    @Id
+    @GeneratedValue
+    private Long id;
+
+    @Column(nullable = false)
+    private String name;
+
+    @Column(nullable = false)
+    private String state;
+
+    // ... additional members, often include @OneToMany mappings
+
+    protected City() {
+        // no-args constructor required by JPA spec
+        // this one is protected since it shouldn't be used directly
+    }
+
+    public City(String name, String state) {
+        this.name = name;
+        this.country = country;
+    }
+
+    public String getName() {
+        return this.name;
+    }
+
+    public String getState() {
+        return this.state;
+    }
+    // ... etc
+}
+```
+**注**：你可以使用@EntityScan注解自定义实体扫描路径。具体参考[Section 67.4, “Separate @Entity definitions from Spring configuration”](http://docs.spring.io/spring-boot/docs/current-SNAPSHOT/reference/htmlsingle/#howto-separate-entity-definitions-from-spring-configuration)。