@Target({METHOD, FIELD})
@Retention(RUNTIME)
public @interface GeneratedValue {
    /**
     * (Optional) The primary key generation strategy
     * that the persistence provider must use to
     * generate the annotated entity primary key.
     */
    GenerationType strategy() default AUTO;
    /**
     * (Optional) The name of the primary key generator
     * to use as specified in the {@link SequenceGenerator} 
     * or {@link TableGenerator} annotation.
     * <p> Defaults to the id generator supplied by persistence provider.
     */
    String generator() default "";
}

/** 
 * Defines the types of primary key generation. 
 *
 * @since Java Persistence 1.0
 */
public enum GenerationType { 
    /**
     * Indicates that the persistence provider must assign 
     * primary keys for the entity using an underlying 
     * database table to ensure uniqueness.
     */
    TABLE, 
    /**
     * Indicates that the persistence provider must assign 
     * primary keys for the entity using database sequence column.
     */
    SEQUENCE, 
    /**
     * Indicates that the persistence provider must assign 
     * primary keys for the entity using database identity column.
     */
    IDENTITY, 
    /**
     * Indicates that the persistence provider should pick an 
     * appropriate strategy for the particular database. The 
     * <code>AUTO</code> generation strategy may expect a database 
     * resource to exist, or it may attempt to create one. A vendor 
     * may provide documentation on how to create such resources 
     * in the event that it does not support schema generation 
     * or cannot create the schema resource at runtime.
     */
    AUTO
}

@Id
@GeneratedValue(strategy = GenerationType.TABLE, generator = "roleSeq")
@TableGenerator(name = "roleSeq", allocationSize = 1, table = "seq_table", pkColumnName = "seq_id", valueColumnName = "seq_count")
private Integer id;

@Id
@GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "menuSeq")
@SequenceGenerator(name = "menuSeq", initialValue = 1, allocationSize = 1, sequenceName = "MENU_SEQUENCE")
private Integer id;

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY,generator = "mysql")
private Integer id;

    @GeneratedValue(strategy = GenerationType.AUTO)
    private Integer id;
	或
    @GeneratedValue
    private Integer id;

// 包名
package tk.mybatis.mapper.mapperhelper;
	//主鍵策略 - Oracle序列，MySql自動(dòng)增長(zhǎng)，UUID
	// Oracle序列生成注解
    if (field.isAnnotationPresent(SequenceGenerator.class)) {
        SequenceGenerator sequenceGenerator = field.getAnnotation(SequenceGenerator.class);
        if (sequenceGenerator.sequenceName().equals("")) {
            throw new RuntimeException(entityTable.getEntityClass() + "字段" + field.getName() + "的注解@SequenceGenerator未指定sequenceName!");
        }
        entityColumn.setSequenceName(sequenceGenerator.sequenceName());
      //MySql自動(dòng)增長(zhǎng)，UUID
    } else if (field.isAnnotationPresent(GeneratedValue.class)) {
        GeneratedValue generatedValue = field.getAnnotation(GeneratedValue.class);
        // 首先 通過generator 類型判斷主鍵生成類型
        if (generatedValue.generator().equals("UUID")) {
            entityColumn.setUuid(true);
        } else if (generatedValue.generator().equals("JDBC")) {
            entityColumn.setIdentity(true);
            entityColumn.setGenerator("JDBC");
            entityTable.setKeyProperties(entityColumn.getProperty());
            entityTable.setKeyColumns(entityColumn.getColumn());
        } else {
            //允許通過generator來(lái)設(shè)置獲取id的sql,例如mysql=CALL IDENTITY(),hsqldb=SELECT SCOPE_IDENTITY()
            //允許通過攔截器參數(shù)設(shè)置公共的generator
            // generator 不是UUID 和 JDBC時(shí) 判斷 strategy ；如果類型不是 GenerationType.IDENTITY 則會(huì)拋出異常
            if (generatedValue.strategy() == GenerationType.IDENTITY) {
                //mysql的自動(dòng)增長(zhǎng)
                entityColumn.setIdentity(true);
                if (!generatedValue.generator().equals("")) {
                    String generator = null;
                    // 獲取generator 主鍵生成的來(lái)源 
                    IdentityDialect identityDialect = IdentityDialect.getDatabaseDialect(generatedValue.generator());
                    if (identityDialect != null) {
                        generator = identityDialect.getIdentityRetrievalStatement();
                    } else {
                        generator = generatedValue.generator();
                    }
                    entityColumn.setGenerator(generator);
                }
            } else {
                throw new RuntimeException(field.getName()
                        + " - 該字段@GeneratedValue配置只允許以下幾種形式:" +
                        "\n1.全部數(shù)據(jù)庫(kù)通用的@GeneratedValue(generator=\"UUID\")" +
                        "\n2.useGeneratedKeys的@GeneratedValue(generator=\\\"JDBC\\\")  " +
                        "\n3.類似mysql數(shù)據(jù)庫(kù)的@GeneratedValue(strategy=GenerationType.IDENTITY[,generator=\"Mysql\"])");
            }
        }
    }
    entityTable.getEntityClassColumns().add(entityColumn);
    if (entityColumn.isId()) {
        entityTable.getEntityClassPKColumns().add(entityColumn);
    }

package tk.mybatis.mapper.code;
public enum IdentityDialect {
    DB2("VALUES IDENTITY_VAL_LOCAL()"),
    MYSQL("SELECT LAST_INSERT_ID()"),
    SQLSERVER("SELECT SCOPE_IDENTITY()"),
    CLOUDSCAPE("VALUES IDENTITY_VAL_LOCAL()"),
    DERBY("VALUES IDENTITY_VAL_LOCAL()"),
    HSQLDB("CALL IDENTITY()"),
    SYBASE("SELECT @@IDENTITY"),
    DB2_MF("SELECT IDENTITY_VAL_LOCAL() FROM SYSIBM.SYSDUMMY1"),
    INFORMIX("select dbinfo('sqlca.sqlerrd1') from systables where tabid=1");
    private String identityRetrievalStatement;
    private IdentityDialect(String identityRetrievalStatement) {
        this.identityRetrievalStatement = identityRetrievalStatement;
    }
    public static IdentityDialect getDatabaseDialect(String database) {
        IdentityDialect returnValue = null;
        if ("DB2".equalsIgnoreCase(database)) {
            returnValue = DB2;
        } else if ("MySQL".equalsIgnoreCase(database)) {
            returnValue = MYSQL;
        } else if ("SqlServer".equalsIgnoreCase(database)) {
            returnValue = SQLSERVER;
        } else if ("Cloudscape".equalsIgnoreCase(database)) {
            returnValue = CLOUDSCAPE;
        } else if ("Derby".equalsIgnoreCase(database)) {
            returnValue = DERBY;
        } else if ("HSQLDB".equalsIgnoreCase(database)) {
            returnValue = HSQLDB;
        } else if ("SYBASE".equalsIgnoreCase(database)) {
            returnValue = SYBASE;
        } else if ("DB2_MF".equalsIgnoreCase(database)) {
            returnValue = DB2_MF;
        } else if ("Informix".equalsIgnoreCase(database)) {
            returnValue = INFORMIX;
        }
        return returnValue;
    }
    public String getIdentityRetrievalStatement() {
        return identityRetrievalStatement;
    }
}