大数据实训第一天总结

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软件工程小学期第一天，学习内容包括：复习JAVA基础知识、熟悉主流框架，总结如下：

1. 输入一组数，计算平均值

程序代码：

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import java.util.Scanner;

public class Average {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner scanner = new Scanner(System.in);
		int s = 0;						// 所有数之和
		int n = 0;						// 数据个数
		System.out.println("输入数据个数");
		n = scanner.nextInt();
		for (int i = 0; i < n; i++) {
			s += scanner.nextInt();
		}
		System.out.println(s / n);

	}

}

执行结果： 实训1-1

2. 定义一个集合类，实现add()、set()、size()、get()方法，要求集合能够自动扩容

实现set()、size()、get()方法较为简单。 本题关键在于如何实现集合类的自动扩容，因为JAVA数组不支持动态修改长度，于是经思考后得出一般思路：集合已满后再添加数据时，创建一个比原来数组更长的数组，并把之前的数据拷贝进新数组，来代替原先长度较小的数组，来实现集合类的自动扩容。

程序代码：

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package demo;

public class MySet {

	private Object[] list;				// 内置数组
	private int length = 0;				// 集合中元素个数
	
	public MySet(int mSize) {
		list = new Object[mSize];
	}
	
	// 添加元素
	public void add(Object object) {
		
		if(length == list.length) {
			Object[] list2 = new Object[2 * list.length];
			for(int i = 0;i < length;i++)
				list2[i] = list[i];
			list = list2;
		}
		
		list[length] = object;
		length++;
	}
	
	// 获取下标为i的元素
	public Object get(int i) {
	    if (i < 0 || i >= length) {
	        throw new IllegalArgumentException("获取失败，参数不能负数以及不能大于当前数组元数个数");
	    }
		return list[i];
	}
	
	// 将下标为i的元素置为obj
	public void set(int i,Object obj) {
		if (i < 0 || i >= length) {
	        throw new IllegalArgumentException("设置失败，设置位置不能负数以及不能大于当前数组元数个数");
	    }
		list[i] = obj;
	}
	
	// 获取集合大小
	public int size() {
		return length;
	}
	
	// 打印
	public static void show(MySet myset) {
		for (int i = 0;i < myset.size();i++) {
			System.out.println("set.get(" + i + "): " + (String)myset.get(i));
		}
	}
	
	public static void main(String[] args) {
		MySet set = new MySet(4);
		set.add("hh");
		set.add("ee");
		set.add("ll");
		set.add("oo");
		set.add("ww");
		set.set(0, "HH");
		show(set);
		System.out.println("set.size(): " + set.size());
	}

}

执行结果： QQ截图20190901090451

3. 实现一个实体的增删改查

为复习框架知识，本程序使用SpringBoot框架实现

  • 实体层 ```java package com.imooc.domain;

import com.fasterxml.jackson.annotation.JsonIgnoreProperties;

import javax.persistence.Entity; import javax.persistence.GeneratedValue; import javax.persistence.Id; import javax.validation.constraints.Min; import java.io.Serializable;

@Entity @JsonIgnoreProperties(value={“hibernateLazyInitializer”,”handler”,”fieldHandler”}) public class Girl {

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@Id
@GeneratedValue
private Integer id;

private String cS;

@Min(value = 18,message = "未成年少女禁止入内")
private Integer age;

public Girl() {
}

public Integer getId() {
    return id;
}

public void setId(Integer id) {
    this.id = id;
}

public String getCS() {
    return cS;
}

public void setCS(String cS) {
    this.cS = cS;
}

public Integer getAge() {
    return age;
}

public void setAge(Integer age) {
    this.age = age;
} } ``` - Service层 ```java package com.imooc.service;

import com.imooc.domain.Girl; import com.imooc.repository.GirlRepository; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.stereotype.Service; import org.springframework.transaction.annotation.Transactional;

@Service public class GirlService {

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@Autowired
private GirlRepository girlRepository;

@Transactional
public void insertTwo(){

    Girl girlA = new Girl();
    girlA.setCS("A");
    girlA.setAge(18);
    girlRepository.save(girlA);

    Girl girlB = new Girl();
    girlB.setCS("BBBB");
    girlB.setAge(19);
    girlRepository.save(girlB);

} } ``` - repository ```java package com.imooc.repository;

import com.imooc.domain.Girl; import org.springframework.data.jpa.repository.JpaRepository;

import java.util.List;

public interface GirlRepository extends JpaRepository<Girl,Integer> {

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public List<Girl> findByAge(Integer age);

}

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- Controller层
```java
package com.imooc.controller;

import com.imooc.domain.Girl;
import com.imooc.repository.GirlRepository;
import com.imooc.service.GirlService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.validation.BindingResult;
import org.springframework.web.bind.annotation.*;

import javax.validation.Valid;
import java.util.List;

@RestController
public class GirlController {

    @Autowired
    private GirlRepository girlRepository;

    @Autowired
    private GirlService girlService;

    //查询所有女生列表
    @GetMapping(value = "/girls")
    public List<Girl> girlList(){
        return girlRepository.findAll();
    }

    //添加一个女生
    @PostMapping(value = "/addGirl")
    public Girl girlAdd(@Valid Girl girl, BindingResult bindingResult){
        if (bindingResult.hasErrors()){
            System.out.println(bindingResult.getFieldError().getDefaultMessage());
            return null;
        }
        girl.setCS(girl.getCS());
        girl.setAge(girl.getAge());
        return girlRepository.save(girl);
    }

    @GetMapping(value = "/girls/{id}")
    public Girl getGirl(@PathVariable("id") Integer id){
        return girlRepository.getOne(id);
    }

    @GetMapping(value = "/updateGirl/{id}")
    public Girl girlUpdate(@PathVariable("id") Integer id,
                           @RequestParam("cS") String cS,
                           @RequestParam("age") Integer age){
        System.out.println("ss");
        Girl girl = new Girl();
        girl.setId(id);
        girl.setAge(age);
        girl.setCS(cS);
        Girl girl1 = girlRepository.save(girl);
        System.out.println(girl.getCS());
        System.out.println(girl.getAge());
        return girl1;
    }

    @GetMapping(value = "/delGirl/{id}")
    public void delGirl(@PathVariable("id") Integer id){
        girlRepository.delete(id);
    }

    @GetMapping(value = "/findByAge/{age}")
    public List<Girl> findByAge(@PathVariable("age") Integer age){
        return girlRepository.findByAge(age);
    }

    @PostMapping(value = "/girls/two")
    public void girlTwo(){
        girlService.insertTwo();
    }
}
  • Properties ```java package com.imooc.properties;

import org.springframework.boot.context.properties.ConfigurationProperties; import org.springframework.stereotype.Component;

@Component @ConfigurationProperties(prefix = “girl”) public class GirlPropertites { private String cS; private Integer age;

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public String getCS() {
    return cS;
}

public void setCS(String cS) {
    this.cS = cS;
}

public Integer getAge() {
    return age;
}

public void setAge(Integer age) {
    this.age = age;
} } ``` - 配置文件 ```yml # application.yml spring:   profiles:
active: dev   datasource:
driver-class-name: com.mysql.jdbc.Driver
url: jdbc:mysql://127.0.0.1:3306/dbgirl
username: root
password: root   jpa:
hibernate:
  ddl-auto: update
show-sql: true

jackson: serialization: FAIL_ON_EMPTY_BEANS: false ``` — 今天的讲课中，再次听到一句老生常谈的话题，即JDBC模式已经过时，当今用最多的仍是三大框架，而Springboot正在流行。