Copy cat > /tmp/Lab12.java << 'JAVAEOF'
import java.lang.annotation.*;
import java.lang.reflect.*;
import java.util.*;
public class Lab12 {
@Retention(RetentionPolicy.RUNTIME) @Target(ElementType.TYPE)
@interface Entity { String table(); }
@Retention(RetentionPolicy.RUNTIME) @Target(ElementType.FIELD)
@interface Column { String name() default ""; boolean nullable() default true; boolean primaryKey() default false; }
@Retention(RetentionPolicy.RUNTIME) @Target(ElementType.METHOD)
@interface Validate { String message() default "Validation failed"; }
@Entity(table = "products")
static class Product {
@Column(name = "id", primaryKey = true, nullable = false) private int id;
@Column(name = "name", nullable = false) private String name;
@Column(name = "price", nullable = false) private double price;
@Column(name = "stock") private int stock;
private String internalField = "skip_me";
Product(int id, String name, double price, int stock) {
this.id=id; this.name=name; this.price=price; this.stock=stock; }
@Validate(message = "price must be positive") boolean priceValid() { return price > 0; }
@Validate(message = "name must not be blank") boolean nameValid() { return name != null && !name.isBlank(); }
}
static String generateInsert(Object entity) throws Exception {
var cls = entity.getClass();
var table = cls.getAnnotation(Entity.class);
if (table == null) throw new IllegalArgumentException("Not an @Entity");
var cols = new ArrayList<String>(); var vals = new ArrayList<String>();
for (var field : cls.getDeclaredFields()) {
var col = field.getAnnotation(Column.class);
if (col == null) continue;
field.setAccessible(true);
cols.add(col.name().isEmpty() ? field.getName() : col.name());
var val = field.get(entity);
vals.add(val instanceof String ? "'" + val + "'" : String.valueOf(val));
}
return "INSERT INTO " + table.table() + " (" + String.join(", ", cols) +
") VALUES (" + String.join(", ", vals) + ")";
}
static List<String> validate(Object entity) throws Exception {
var errors = new ArrayList<String>();
for (var method : entity.getClass().getDeclaredMethods()) {
var v = method.getAnnotation(Validate.class);
if (v == null) continue;
method.setAccessible(true);
if (Boolean.FALSE.equals(method.invoke(entity))) errors.add(v.message());
}
return errors;
}
static void inspectSchema(Class<?> cls) {
var entity = cls.getAnnotation(Entity.class);
if (entity == null) return;
System.out.println("Table: " + entity.table());
System.out.println("Columns:");
for (var field : cls.getDeclaredFields()) {
var col = field.getAnnotation(Column.class);
if (col == null) continue;
System.out.printf(" %-15s -> %-15s PK=%-5b nullable=%b%n",
field.getName(), col.name().isEmpty() ? field.getName() : col.name(),
col.primaryKey(), col.nullable());
}
}
static class Repo<T> {
private final Class<T> type; private final Map<Integer, T> store = new LinkedHashMap<>();
Repo(Class<T> type) { this.type = type; }
void save(T obj) throws Exception {
for (var f : type.getDeclaredFields()) {
if (f.isAnnotationPresent(Column.class) && f.getAnnotation(Column.class).primaryKey()) {
f.setAccessible(true); store.put((Integer) f.get(obj), obj); return;
}
}
}
int size() { return store.size(); }
Collection<T> findAll() { return store.values(); }
String tableName() { var e = type.getAnnotation(Entity.class); return e != null ? e.table() : type.getSimpleName(); }
}
public static void main(String[] args) throws Exception {
var p1 = new Product(1, "Surface Pro", 864.0, 15);
var p2 = new Product(2, "Surface Pen", 49.99, 80);
var pBad = new Product(3, "", -1.0, 0);
System.out.println("=== Schema Inspection ===");
inspectSchema(Product.class);
System.out.println("\n=== SQL Generation ===");
System.out.println(generateInsert(p1));
System.out.println(generateInsert(p2));
System.out.println("\n=== Validation ===");
System.out.println("p1 valid: " + validate(p1).isEmpty());
System.out.println("pBad errors: " + validate(pBad));
System.out.println("\n=== Generic Repository ===");
var repo = new Repo<>(Product.class);
repo.save(p1); repo.save(p2);
System.out.println("Table: " + repo.tableName() + " | Size: " + repo.size());
repo.findAll().forEach(p -> {
try {
var f = Product.class.getDeclaredField("name"); f.setAccessible(true);
System.out.println(" " + f.get(p));
} catch (Exception e) {}
});
System.out.println("\n=== Class Introspection ===");
var cls = Product.class;
System.out.println("Class: " + cls.getSimpleName());
System.out.println("Annotations: " + Arrays.stream(cls.getAnnotations()).map(a -> a.annotationType().getSimpleName()).toList());
System.out.println("Methods: " + Arrays.stream(cls.getDeclaredMethods()).map(Method::getName).toList());
System.out.println("Fields: " + Arrays.stream(cls.getDeclaredFields()).map(Field::getName).toList());
System.out.println("Modifiers: " + Modifier.toString(cls.getModifiers()));
}
}
JAVAEOF
docker run --rm -v /tmp/Lab12.java:/tmp/Lab12.java zchencow/innozverse-java:latest sh -c "javac /tmp/Lab12.java -d /tmp && java -cp /tmp Lab12" 