如题所示: 尝试手写简易的mybatis框架, 参照大佬的文章,写出来后在代码中加了部分注解,以此记录当做学习过程
参照原文链接: https://blog.csdn.net/l1028386804/article/details/117409076
提供Table 注解
package test.orm;
import java.lang.annotation.*;
@Inherited
@Target({
ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Table {
String value() default "";
}
提供Column 注解
package test.orm;
import java.lang.annotation.*;
@Inherited
@Target({
ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Column {
String value() default "";
}
实体类 所用的两个注解均为自己提供的注解
package test.orm;
@Table("table_name")
public class Entity {
public Entity() {
}
public Entity(String userName, Integer age, String sex) {
this.userName = userName;
this.age = age;
this.sex = sex;
}
@Column("user_name")
private String userName;
@Column("age")
private Integer age;
@Column("sex")
private String sex;
public String getUserName() {
return userName;
}
public void setUserName(String userName) {
this.userName = userName;
}
public Integer getAge() {
return age;
}
public void setAge(Integer age) {
this.age = age;
}
public String getSex() {
return sex;
}
public void setSex(String sex) {
this.sex = sex;
}
}
核心代码 根据实体类创建sql
package test.orm;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
public class SqlBuilder {
public static String assembleSqlFromObj(Object obj) {
Table table = obj.getClass().getAnnotation(Table.class);
StringBuffer sbSql = new StringBuffer();
String tableName = table.value();
sbSql.append("select * from " + tableName + " where 1 = 1 ");
Field[] fileds = obj.getClass().getDeclaredFields();
for (Field f : fileds) {
String fieldName = f.getName();
String methodName = "get" + fieldName.substring(0, 1).toUpperCase() + fieldName.substring(1);
try {
Column column = f.getAnnotation(Column.class);
if (column != null) {
Method method = obj.getClass().getMethod(methodName);
Object v = method.invoke(obj);
if (v != null) {
if (v instanceof String) {
String value = v.toString().trim();
if (value.contains(",")) {
String sqlParams = value.replace(",", "").trim();
if (isNum(sqlParams)) {
sbSql.append(" and " + column.value() + " in (" + value + ") ");
} else {
String[] split = value.split(",");
value = "";
for (int i = 0; i < split.length - 1; i++) {
value += "'" + split[i] + "',";
}
value += "'" + split[split.length - 1] + "'";
sbSql.append(" and " + column.value() + " in (" + value + ") ");
}
} else {
if (value.length() > 0) {
sbSql.append(" and " + column.value() + " like '%" + value + "%' ");
}
}
} else {
sbSql.append(" and " + column.value() + " = " + v.toString() + " ");
}
}
}
} catch (Exception e) {
e.printStackTrace();
}
}
return sbSql.toString();
}
private static boolean isNum(String target) {
boolean isNum = false;
if (target.matches("\\d+")) {
isNum = true;
}
return isNum;
}
}
进行测试
package test.orm;
public class Test {
public static void main(String[] args) {
Entity entity = new Entity("张三", 18, "男");
Entity entity1 = new Entity("张三", null, null);
String sql1 = SqlBuilder.assembleSqlFromObj(entity);
String sql2 = SqlBuilder.assembleSqlFromObj(entity1);
System.out.println(sql1);
System.out.println(sql2);
}
}
测试结果: