首发于Enaium的个人博客
不用XML只用注解
首先需要创建6个注解
SQL用于输入SQL语句
@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
public @interface SQL {
String[] value();
}
用来表示这个方法是Update
@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
public @interface Update {
}
用来表示这个方法是Select
@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
public @interface Select {
}
用来表示这个方法是Insert
@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
public @interface Insert {
}
用来表示这个方法是Delete
@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
public @interface Delete {
}
用来表示方法参数名
@Target(ElementType.PARAMETER)
@Retention(RetentionPolicy.RUNTIME)
public @interface Param {
String value();
}
好了注解写完了
开始写主类
用map实现简单的配置，然后读取配置连接数据库，然后程序关闭的时候关闭连接。
public class Satis {
private final Statement statement;
public Satis(Map<String, String> config) throws Exception {
Class.forName(config.get("driver"));
Connection connection = DriverManager.getConnection(config.get("url"), config.get("username"), config.get("password"));
statement = connection.createStatement();
Runtime.getRuntime().addShutdownHook(new Thread(() -> {
try {
statement.close();
connection.close();
} catch (SQLException e) {
e.printStackTrace();
}
}));
}
}
创建getMapper方法。
public <T> T getMapper(Class<?> mapper) {
}
使用动态代理。
public <T> T getMapper(Class<?> mapper) {
Object instance = Proxy.newProxyInstance(mapper.getClassLoader(), new Class<?>[]{
mapper}, new InvocationHandler() {
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
return null;
}
};
return (T) instance;
}
遍历方法获取方法是否有SQL这个注解。
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
if (method.isAnnotationPresent(SQL.class)) {
}
return null;
}
创建4个方法，分别获取方法是否有这几个注解。
private boolean isSelect(Method method) {
return method.isAnnotationPresent(Select.class);
}
private boolean isDelete(Method method) {
return method.isAnnotationPresent(Delete.class);
}
private boolean isInsert(Method method) {
return method.isAnnotationPresent(Insert.class);
}
private boolean isUpdate(Method method) {
return method.isAnnotationPresent(Update.class);
}
遍历SQL注解的值。
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
if (method.isAnnotationPresent(SQL.class)) {
SQL sql = method.getAnnotation(SQL.class);
for (String value : sql.value()) {
}
}
return null;
}
获取方法上是否有Select或Delete注解，是的话把SQL参数的值(获取参数的Param注解的值)替换为调用方法时的参数。
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
if (method.isAnnotationPresent(SQL.class)) {
SQL sql = method.getAnnotation(SQL.class);
for (String value : sql.value()) {
if (isSelect(method) || isDelete(method)) {
int index = 0;
for (Parameter parameter : method.getParameters()) {
if (parameter.isAnnotationPresent(Param.class)) {
Param param = parameter.getAnnotation(Param.class);
value = value.replace("#{" + param.value() + "}", args[index].toString());
}
index++;
}
}
}
}
return null;
}
如果是Insert或Update注解，获取第一个参数，获取这个参数的所有方法并获取值。
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
if (method.isAnnotationPresent(SQL.class)) {
SQL sql = method.getAnnotation(SQL.class);
for (String value : sql.value()) {
if (isInsert(method) || isUpdate(method)) {
Class<?> parameterType = method.getParameterTypes()[0];
for (Field declaredField : parameterType.getDeclaredFields()) {
value = value.replace("#{" + declaredField.getName() + "}", "\"" + parameterType.getMethod(getGetMethodName(declaredField.getName())).invoke(args[0]).toString() + "\"");
}
}
}
}
return null;
}
简单的获取方法名的方法。
private String getSetMethodName(String name) {
return "set" + name.substring(0, 1).toUpperCase(Locale.ROOT) + name.substring(1);
}
private String getGetMethodName(String name) {
return "get" + name.substring(0, 1).toUpperCase(Locale.ROOT) + name.substring(1);
}
执行SQL语句，如果有返回值那就返回实例化。
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
if (method.isAnnotationPresent(SQL.class)) {
SQL sql = method.getAnnotation(SQL.class);
for (String value : sql.value()) {
String typeName = method.getGenericReturnType().getTypeName();
ResultSet resultSet = statement.executeQuery(value);
if (!typeName.equals("void")) {
return toEntity(resultSet, typeName);
}
}
}
return null;
}
将返回值实例化。
private <T> T toEntity(ResultSet resultSet, String className) throws SQLException, NoSuchMethodException, InvocationTargetException, IllegalAccessException, InstantiationException, ClassNotFoundException {
boolean list = className.contains("<");//是不是列表
if (list) {
className = className.substring(className.indexOf("<") + 1, className.lastIndexOf(">"));//获取列表的泛型
}
Class<?> klass = Class.forName(className);
HashMap<String, Class<?>> fieldNameList = new HashMap<>();
for (int i = 0; i < resultSet.getMetaData().getColumnCount(); i++) {
//获取字段和参数
fieldNameList.put(resultSet.getMetaData().getColumnName(i + 1), Class.forName(resultSet.getMetaData().getColumnClassName(i + 1)));
}
List<Object> objectList = new ArrayList<>();
while (resultSet.next()) {
Object instance = klass.newInstance();//实例化
for (Map.Entry<String, Class<?>> entry : fieldNameList.entrySet()) {
//遍历字段
//调用set方法赋值
klass.getMethod(getSetMethodName(entry.getKey()), entry.getValue()).invoke(instance, resultSet.getObject(entry.getKey(), entry.getValue()));
}
objectList.add(instance);//添加到列表
}
resultSet.close();//关闭
if (objectList.isEmpty()) {
return null;//如果列表为空返回null
}
return list ? (T) objectList : (T) objectList.get(0);//判断是否为列表，如果是直接返回，如果不是取第一个
}
好了已经写完了。
现在来测试
实体
@Data
@AllArgsConstructor
public class AccountEntity {
private Long id;
private String name;
private Integer age;
public AccountEntity() {
//用了lombok就不会自动生成无参构造方法了
}
}
接口
public interface AccountMapper {
@Select
@SQL("select * from account")
List<AccountEntity> getAll();
@Select
@SQL("select * from account where id = #{id}")
AccountEntity getById(@Param("id") Serializable id);
@Delete
@SQL("delete from account where id = #{id}")
void deleteById(@Param("id") Serializable id);
@Insert
@SQL("insert into account(id, name, age) values (#{id}, #{name}, #{age})")
void insert(AccountEntity accountEntity);
@Update
@SQL("update account set name=#{name}, age=#{age} where id=#{id}")
void update(AccountEntity accountEntity);
}
主类
public class Main {
public static void main(String[] args) throws Exception {
Satis satis = new Satis(ImmutableMap.of(
"url", "jdbc:mariadb://localhost:3306/enaium?useUnicode=true&characterEncoding=UTF-8",
"driver", "org.mariadb.jdbc.Driver",
"username", "root",
"password", "root"));//使用guava
AccountMapper mapper = satis.getMapper(AccountMapper.class);//获取Mapper
System.out.println(mapper.getById(1));//获取ID为1的Account
mapper.getAll().forEach(System.out::println);//获取所有Account
mapper.insert(new AccountEntity(0L, "Enaium", 1));//插入一个新的Account
mapper.getAll().forEach((it) -> {
//把所有Account的Age都改为0
it.setAge(0);
mapper.update(it);
});
}
}
