如何使用反射来基于JPA注释记录数据模型

因此，当您仅可以注释Java类时，使用JPA，Hibernate或EBeans会很酷，但是您不是一直希望可以从代码“生成”数据模型的文档吗？提取JPA / Hibernate和其他验证批注的信息？

假设您的bean中包含所有这些漂亮的注释：

@Entity
@Table(name = "project_bills")
public class Bill extends Model {private static final long serialVersionUID = 1L;@Id@Column(name="PBI_ID")public Long id;@DoubleFormat@Column(name="PBI_BILL_AMOUNT",length=22)public Double billAmount;@Column(name="PBI_BILL_DATE")@DateTime(pattern="dd.MM.yyyy")public Date billDate;@Column(name="PBI_BILL_NUMBER",length=10)public String billNumber;@Column(name="PBI_CAN_BILL")public Boolean canBill;@Column(name="PBI_COMMENT",length=65535)public String comment;@Column(name="PBI_PAID_DATE")@DateTime(pattern="dd.MM.yyyy")public Date paidDate;

这是如何完成该任务的示例：

public static String listEntities(String _package) {StringBuffer retval = new StringBuffer();Reflections reflections = new Reflections(_package, Play.application().classloader());Set<Class<?>> classes = reflections.getTypesAnnotatedWith(javax.persistence.Entity.class);for (Class c : classes) {retval.append(c.getName() + "\n");retval.append(listAnnotations(c.getName()) + "\n\n");retval.append(listAttributes(c.getName()) + "\n\n");}return retval.toString();}public static String listAnnotations(String _class) {StringBuffer retval = new StringBuffer();try {Annotation[] annotations = Class.forName(_class).getAnnotations();if (annotations.length != 0) {for (int j = 0; j < annotations.length; j++) {retval.append(annotations[j].toString() + ": " + annotations[j].annotationType() + "\n");}retval.append("\n");}} catch (ClassNotFoundException e) {System.out.println(e.toString());return retval.toString();}return retval.toString();}public static String listAttributes(String _class) {StringBuffer retval2 = new StringBuffer();boolean perstistent = false;try {for (Field field : Class.forName(_class).getDeclaredFields()) {Class type = field.getType();String name = field.getName();perstistent = false;StringBuffer retval = new StringBuffer();retval.append("\t" + name + " (" + type + ")\n");Annotation[] annotations = field.getDeclaredAnnotations();if (annotations.length != 0) {for (int j = 0; j < annotations.length; j++) {retval.append(annotations[j].toString() + ": " + annotations[j].annotationType() + "\n");if (annotations[j].toString().startsWith("@javax.persistence")) {perstistent = true;}}retval.append("\n");}if (perstistent) {retval2.append(retval);}}} catch (ClassNotFoundException e) {System.out.println(e.toString());return retval2.toString();}return retval2.toString();}

这将生成如下内容：

models.controlling.Bill
@javax.persistence.Table(schema=, uniqueConstraints=[], catalog=, name=project_bills): interface javax.persistence.Table
@javax.persistence.Entity(name=): interface javax.persistence.Entityid (class java.lang.Long)
@javax.persistence.Id(): interface javax.persistence.Id
@javax.persistence.Column(insertable=true, scale=0, unique=false, precision=0, columnDefinition=, name=PBI_ID, updatable=true, length=255, nullable=true, table=): interface javax.persistence.ColumnbillAmount (class java.lang.Double)
@utils.data.formatters.Formats$DoubleFormat(): interface utils.data.formatters.Formats$DoubleFormat
@javax.persistence.Column(insertable=true, scale=0, unique=false, precision=0, columnDefinition=, name=PBI_BILL_AMOUNT, updatable=true, length=22, nullable=true, table=): interface javax.persistence.ColumnbillDate (class java.util.Date)
@javax.persistence.Column(insertable=true, scale=0, unique=false, precision=0, columnDefinition=, name=PBI_BILL_DATE, updatable=true, length=255, nullable=true, table=): interface javax.persistence.Column
@play.data.format.Formats$DateTime(pattern=dd.MM.yyyy): interface play.data.format.Formats$DateTimebillNumber (class java.lang.String)
@javax.persistence.Column(insertable=true, scale=0, unique=false, precision=0, columnDefinition=, name=PBI_BILL_NUMBER, updatable=true, length=10, nullable=true, table=): interface javax.persistence.Column

当然，这只是冰山一角，但是您明白了。

参考： 如何使用 Poornerd博客上的JCG合作伙伴 Brian Porter的JPA注释，如何使用反射来记录数据模型。