public class ArrayList<T> {
    private T[] array;
    private int size;
    public void add(T e) {...}
    public void remove(int index) {...}
    public T get(int index) {...}
}

T可以是任何class。这样一来，我们就实现了：编写一次模版，可以创建任意类型的ArrayList：

2021-10-25发表2021-10-25更新java1 分钟读完 (大约114个字)

读取txt文件

public class ReadFileByLines {
	public static void main(String[] args) {
		try {
			//1.打开一个file
			File file = new File("E:/test.txt");
			//2.InputStreamReader<-FileInputStream<-file
			FileInputStream fis = new FileInputStream(file);
			InputStreamReader is = new InputStreamReader(fis);
			//3.用BufferedReader(<-InputStreamReader)的readLine()方法读取
			BufferedReader br = new BufferedReader(is);

			//4.输出
			String txtLine = null;
			while ((txtLine = br.readLine()) != null) {
				System.out.println(txtLine);
			}
			br.close();
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}

public class ReadFileByLines {
	public static void main(String[] args) {
		try {
			
			File file = new File("E:/test.txt");
			
			BufferedReader br = new BufferedReader(new FileReader(file));
			
			String txtLine = null;
			while ((txtLine = br.readLine()) != null) {
				System.out.println(txtLine);
			}
			br.close();
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}

2021-10-25发表2021-10-26更新java1 分钟读完 (大约199个字)

bind header to controller


import javax.servlet.http.HttpServletRequest;

import org.springframework.core.MethodParameter;
import org.springframework.web.bind.support.WebDataBinderFactory;
import org.springframework.web.context.request.NativeWebRequest;
import org.springframework.web.method.support.HandlerMethodArgumentResolver;
import org.springframework.web.method.support.ModelAndViewContainer;

import lombok.extern.slf4j.Slf4j;
import summer.webserver.util.SummerUtils;

@Slf4j
public class SummerArgumentResolver implements HandlerMethodArgumentResolver {

	public SummerArgumentResolver() {
		super();
	}

	@Override
	public boolean supportsParameter(MethodParameter parameter) {
		return SummerHeader.class.isAssignableFrom(parameter.getParameterType());
	}

	@Override
	public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer,
		NativeWebRequest webRequest, WebDataBinderFactory binderFactory) {
		return SummerUtils.getSummerHeader(webRequest.getNativeRequest(HttpServletRequest.class));
	}
}


@Slf4j
public class SummerUtils {
	public static SummerHeader getSummerHeader(HttpServletRequest request) {
		User user = (User)request.getAttribute("user");
		String userName = Objects.isNull(user) ? request.getHeader(USER_NAME) : user.getUserName();
		String userId = Objects.isNull(user) ? request.getHeader(USER_ID) : user.getUserId();
		SummerHeader summerHeader = SummerHeader.builder()
			.userName(userName)
			.userId(userId)
			.build();

		if (log.isDebugEnabled()) {
			log.debug(summerHeader.toString());
		}
		request.setAttribute("summerHeader", summerHeader);
		return summerHeader;
	}
}

usage


@Api(tags = "User")
@RestController()
@RequestMapping(ROOT_DOMAIN + "/users")
@Slf4j
public class UserController {
	@ApiOperation(value = "delete user")
	@DeleteMapping("/{user-id}")
	@ResponseStatus(HttpStatus.OK)
	public void deleteUser(SummerHeader summerHeader,
		@ApiParam(required = true) @Length(max = 10) @PathVariable(value = "user-id") String userId) {
		userMapper.deleteById(userId);
	}
}

2021-10-25发表2022-06-24更新java2 分钟读完 (大约245个字)

java多线程那点事

java多线程那点事|提升java能力
 阿里面试官的分享Java面试中需要准备哪些多线程并发的技术要点

2021-10-14发表2021-10-14更新java2 分钟读完 (大约328个字)

some parameters that only one is not null valid

注解

@Documented
@Target({ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
public @interface CustomValid {

}

@Documented
@Constraint(validatedBy = OnlyOneNotNullValidator.class)
@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
public @interface OnlyOneNotNull {

	String message() default "only one filed should not be null";

	Class<?>[] groups() default {};

	Class<? extends Payload>[] payload() default {};

	String[] fieldNames();

}

2021-10-14发表2021-10-14更新java1 分钟读完 (大约154个字)

时间格式注解验证

EnumValid.java


@Constraint(validatedBy = DateFormatValidator.class)
@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
public @interface DateFormat {
	String message() default "";

	String pattern() default "yyyy-MM-dd HH:mm:ss";

	Class<?>[] groups() default {};

	Class<? extends Payload>[] payload() default {};
}

CompletableFuture基本用法

对比

ConfigurationProperties

java 多态 Polymorphic

简述

多态的语法格式

java 泛型 Generics

简述

读取txt文件

bind header to controller

usage

java多线程那点事

some parameters that only one is not null valid

注解

时间格式注解验证

EnumValid.java

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