框架

三层架构

• controller：控制层，接收前端发送的请求，对请求进行处理并响应数据
• service：业务逻辑层，处理具体的业务逻辑
• dao：数据访问层(持久层)，负责数据访问操作

//service层
package com.example.service;

import java.io.IOException;
import java.util.Map;


public interface PrintFileContentService {
    Map<String,String> printContentFromUrlFile() throws IOException;
}

//serviceImpl
package com.example.service;

import com.example.dao.UrlFileDao;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.URL;
import java.net.URLConnection;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;

@Service
public class PrintFileContentServiceImpl implements PrintFileContentService {
    @Autowired
    private UrlFileDao urlFileDao;

    @Override
    public Map<String,String> printContentFromUrlFile() throws IOException {
        List<String> urls = urlFileDao.readAllUrls();
        Map<String, String> result = new LinkedHashMap<>();

        for (String urlStr : urls) {
            if (urlStr == null || urlStr.trim().isEmpty()) {
                continue;
            }
            try {
                URL url = new URL(urlStr);
                URLConnection con = url.openConnection();
                StringBuilder content = new StringBuilder();
                try (BufferedReader reader = new BufferedReader(
                        new InputStreamReader(con.getInputStream()))) {
                    String line;
                    while ((line = reader.readLine()) != null) {
                        content.append(line).append("\n");  // 收集每一行
                    }
                }
                result.put(urlStr, content.toString());
            } catch (Exception e) {
                result.put(urlStr, "Error: " + e.getMessage());
            }
        }
        return result;
    }

}

//dao层
package com.example.dao;

import java.io.IOException;
import java.util.List;

public interface UrlFileDao {
    List<String> readAllUrls() throws IOException;
}


//daoImpl
package com.example.dao;

import org.springframework.core.io.ClassPathResource;
import org.springframework.stereotype.Repository;

import java.io.BufferedReader;
import java.io.File;
import java.io.IOException;
import java.io.InputStreamReader;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Path;
import java.util.List;

@Repository
public class UrlFileDaoImpl implements UrlFileDao {
    private static final String URL_FILE_PATH="url.txt";

    /**
     *获取文件数据
     */
    @Override
    public List<String> readAllUrls() throws IOException {
        ClassPathResource resource = new ClassPathResource(URL_FILE_PATH);
        try(BufferedReader reader = new BufferedReader(new InputStreamReader(resource.getInputStream(), StandardCharsets.UTF_8))){
            return reader.lines().toList();
        }
    }
}

//controller层
package com.example.controller;

import com.example.dao.UrlFileDao;
import com.example.service.PrintFileContentService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

import java.io.IOException;
import java.util.Map;

@RestController
public class PrintFileContentController {
    @Autowired
    private  PrintFileContentService printService;

    @GetMapping("/list")
    public Map<String,String> PrintFileContent() throws IOException {
        return printService.printContentFromUrlFile();
    }

}

IOC容器管理

@RestController则是@Controller的衍生注解。

如果在声明bean的时候没有指定名字，默认使用类名首字母小写。

声明bean的注解想要生效需要被组件扫描注解@ComponentScan扫描。该注解被启动类声明注解@SpringBootApplication包含在其中，@SpringBootApplication默认扫描范围是启动类所在包及其子包。

DI(依赖注入)

基于@Autowired进行依赖注入的常见方式有三种：

• 属性注入

@RestController
public class PrintFileContentController {
    @Autowired
    private  PrintFileContentService printService;
    //......
}

• 构造函数注入

当只有一个构造函数时，@Autowired可以省略不写

@RestController
public class PrintFileContentController {
    private final PrintFileContentService printService;
    @Autowired
    public PrintFileContentController(PrintFileContentService printService){
        this.printService=printService;
    }
}

• setter注入

@RestController
public class PrintFileContentController {
    private PrintFileContentService printService;
    @Autowired
    public setPrintFileContentController(PrintFileContentService printService){
        this.printService=printService;
    }
}

@Autowired注解默认是按照类型进行注入的，当存在多个相同类型的bean时会报错。

有三种方式能解决：

• @Primary

@Primary
@Service
public class PrintFileContentServiceImpl implements PrintFileContentService {
    @Autowired
    private UrlFileDao urlFileDao;
    //......
}

• @Qualifier，注意首字母一定要小写

@RestController
public class PrintFileContentController {
    @Autowired
    @Qualifier("printFileContentServiceImpl")
    private  PrintFileContentService printService;

• @Resource

@RestController
public class PrintFileContentController {
    @Resource(name="printFileContentServiceImpl")
    private  PrintFileContentService printService;

@Autowired是spring框架提供的注解，@Resource是JavaEE规范提供的；

@Autowired默认按照类型注入，@Resource默认按照名称注入。