实体使用注解：这里是运用了运行时候处理注解，所以RetentionPolicy.RUNTIME
| package whut.annotationDB; @DBTable(name="MEMBER") public class Member { //在使用注解过程中，如果有元素是value，并且只有value需要赋值， //则只需要在()中将值写入 @SQLString(30) private String firstName; @SQLString(50) private String lastName; @SQLInteger private Integer age; @SQLString(value=30,constraints=@Constraints(primaryKey=true)) private String handle; public String getFirstName() { return firstName; } public void setFirstName(String firstName) { this.firstName = firstName; } public String getLastName() { return lastName; } public void setLastName(String lastName) { this.lastName = lastName; } public Integer getAge() { return age; } public void setAge(Integer age) { this.age = age; } public String getHandle() { return handle; } public void setHandle(String handle) { this.handle = handle; } } |
具体的非apt实现的注解处理器：
| package whut.annotationDB; import java.lang.annotation.Annotation; import java.lang.reflect.Field; import java.sql.Connection; import java.sql.DriverManager; import java.sql.PreparedStatement; import java.sql.SQLException; import java.util.ArrayList; import java.util.List; public class TableCreator { public Connection getConnection() { String user = "root"; String password = ""; String serverUrl = "jdbc:mysql://localhost:3306/carrent?user=root&password="; try { Class.forName("com.mysql.jdbc.Driver"); Connection con = DriverManager.getConnection(serverUrl, user, password); return con; } catch (Exception e) { e.printStackTrace(); return null; } } //实现创建表 public static void main(String[] args) { TableCreator tc = new TableCreator(); tc.executeCreateDB(Member.class); } public void executeCreateDB(Class<?> entity) { String sqlStr = explainAnnotation(entity); Connection con = getConnection(); PreparedStatement psql = null; if (con != null && !sqlStr.equals("error")) { try { psql = con.prepareStatement(sqlStr); psql.execute(); } catch (SQLException e) { e.printStackTrace(); } catch (Exception e) { e.printStackTrace(); } finally { try { if (psql != null) psql.close(); } catch (SQLException e) { e.printStackTrace(); } try { if (con != null) psql.close(); } catch (SQLException e) { e.printStackTrace(); } } } else System.out.println("failure to..."); } // 真正的处理器,Class<?>必须用这个表明 public String explainAnnotation(Class<?> entity) { // 获取指定类型的注解 DBTable dbtable = entity.getAnnotation(DBTable.class); if (dbtable == null) { System.out.println("No DBTable annotation in class" + entity.getName()); return "error"; } else { String tableName = dbtable.name();// 获取注解name值，即表名称 // 当没有设置name值，直接利用类的名作为表名 if (tableName.length() < 1) tableName = entity.getName().toUpperCase();// 转换大写 // 准备处理字段注解 List<String> columnsDefs = new ArrayList<String>(); // 获取该类的所有字段 for (Field field : entity.getDeclaredFields()) { String columnName = null; // 获取该字段所有的注解 Annotation[] anns = field.getDeclaredAnnotations(); // Annotation[] anns=field.getAnnotations(); // 当有注解的时候 if (anns.length >= 1) { // 判断注解的类型 if (anns[0] instanceof SQLInteger) { SQLInteger sInt = (SQLInteger) anns[0]; // 当没有name时候，将字段大写为列名 if (sInt.name().length() < 1) columnName = field.getName().toUpperCase(); else columnName = sInt.name(); columnsDefs.add(columnName + " INT" + getConstraints(sInt.constraints())); } if (anns[0] instanceof SQLString) { SQLString sString = (SQLString) anns[0]; // 当没有name时候，将字段大写为列名 if (sString.name().length() < 1) columnName = field.getName().toUpperCase(); else columnName = sString.name(); columnsDefs.add(columnName + " VARCHAR(" + sString.value() + ")" + getConstraints(sString.constraints())); } } } StringBuilder createDB = new StringBuilder("CREATE TABLE " + tableName + "("); for (String cols : columnsDefs) createDB.append(" " + cols + ","); // 移除最后一个，号 String tableSQL = createDB.substring(0, createDB.length() - 1) + ");"; // 输出创建表的过程 System.out.println("Table Creation SQL is:\n" + tableSQL); return tableSQL; } } // 返回指定的约束 public String getConstraints(Constraints con) { String constras = ""; if (!con.allowNull()) constras += " NOT NULL"; if (con.primaryKey()) constras += " PRIMARY KEY"; if (con.unique()) constras += " UNIQUE"; return constras; } } |
