# java学习

**Repository Path**: corgile/java-learning

## Basic Information

- **Project Name**: java学习
- **Description**: 学习
- **Primary Language**: Unknown
- **License**: Not specified
- **Default Branch**: master
- **Homepage**: None
- **GVP Project**: No

## Statistics

- **Stars**: 0
- **Forks**: 0
- **Created**: 2022-02-26
- **Last Updated**: 2022-02-28

## Categories & Tags

**Categories**: Uncategorized

**Tags**: None

## README

## 整合 Jackson 和 Gson

1.   将服务的返回的对象序列化成json字符串
2.   将前端传来的json字符串反序列化成对象

所有的Json生成都需要相关的 HttpMessageConverter

SpringBoot 中自动配置了Jackson和Gson的HttpMessageConverter，

>   如何配置全局 json 格式（比如说日期格式）

1.   创建配置类

     <img src="https://gitee.com/corgile/images/raw/master/images/2021/image-20220226154052274.png" alt="image-20220226154052274" style="zoom: 80%;" />

2.   手动提供一个converter的 bean

     ```java
     package com.a.bootweb.config;
     
     import com.fasterxml.jackson.databind.ObjectMapper;
     import org.springframework.context.annotation.Bean;
     import org.springframework.context.annotation.Configuration;
     import org.springframework.http.converter.json.MappingJackson2HttpMessageConverter;
     
     import java.text.SimpleDateFormat;
     
     @Configuration
     public class WebConfig {
     	@Bean
     	MappingJackson2HttpMessageConverter mapping() {
     		MappingJackson2HttpMessageConverter converter = new MappingJackson2HttpMessageConverter();
     		ObjectMapper om = new ObjectMapper();
             // 设置全局统一日期格式
     		om.setDateFormat(new SimpleDateFormat("yy-MM-dd"));
     		converter.setObjectMapper(om);
     		return converter;
     	}
     }
     
     ```

     

3.   或者也可以：因为真正起作用的是`ObjectMapper` 

     ```java
     package com.a.bootweb.config;
     
     import com.fasterxml.jackson.databind.ObjectMapper;
     import org.springframework.context.annotation.Bean;
     import org.springframework.context.annotation.Configuration;
     
     import java.text.SimpleDateFormat;
     
     @Configuration
     public class WebConfig {
     
     	@Bean
     	public ObjectMapper mapper() {
     		ObjectMapper om = new ObjectMapper();
     		om.setDateFormat(new SimpleDateFormat("MM-dd-yyyy"));
     		return om;
     	}
     }
     ```

## 全局异常处理

```java
package com.a.bootweb.controller;
 
 import org.omg.CosNaming.NamingContextPackage.NotFound;
 import org.springframework.web.bind.annotation.ControllerAdvice;
 import org.springframework.web.bind.annotation.ExceptionHandler;
 import org.springframework.web.bind.annotation.RestControllerAdvice;
 import org.springframework.web.servlet.NoHandlerFoundException;
 
 import javax.servlet.http.HttpServletResponse;
 import java.io.IOException;
 import java.io.PrintWriter;
 @RestControllerAdvice
 public class MyExceptionHandler {
 	@ExceptionHandler(NoHandlerFoundException.class)
 	public void notFound(HttpServletResponse response) throws IOException {
 		response.setContentType("text/html;charset=utf-8");
 		PrintWriter out = response.getWriter();
 		out.write("<h1>404 Not Found! 找不到服务器</h1>");
 		out.flush();
 		out.close();
 	}
 }
```

404需要配置：

```properties
spring.mvc.throw-exception-if-no-handler-found=true
```

## 跨域

1.   跨域注解可以写在方法或类上，也可以写在全局配置中

```java
package com.a.bootweb.config;

import com.fasterxml.jackson.databind.ObjectMapper;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.CorsRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;

import java.text.SimpleDateFormat;

/**
 * @author Corgile
 * @date 2022-02-26
 */
@Configuration
public class WebConfig implements WebMvcConfigurer {
	@Bean
	public ObjectMapper mapper() {
		ObjectMapper om = new ObjectMapper();
		om.setDateFormat(new SimpleDateFormat("MM-dd-yyyy"));
		return om;
	}

	@Override
	public void addCorsMappings(CorsRegistry registry) {
		registry.addMapping("/user/**")
				.allowedOrigins("http://localhost:8081")
				.allowedHeaders("*")
				.allowedMethods("*") //.allowedMethods("/getuser", "/setuser")
				.maxAge(30 * 1000);
	}
}
```



## AOP

定义切点：在service所有方法执行时

```java
@Pointcut(value = "execution(* com.a.bootweb.service.*.*(..))")
public void pointCutForServices() { }
```

各种通知类型

```java
@Before(value = "pointCutForServices()")
public void before(JoinPoint joinPoint) {
	String name = joinPoint.getSignature().getName();
	System.out.println("before-----" + name);
}

@After(value = "pointCutForServices()")
public void after(JoinPoint joinPoint) {
	String name = joinPoint.getSignature().getName();
		System.out.println("after-----" + name);
}

@AfterReturning(value = "pointCutForServices()", returning = "result")
public void afterReturning(JoinPoint joinPoint, Object result) {
	String name = joinPoint.getSignature().getName();
	System.out.println("afterReturning----" + name + "---" + result);
}

@AfterThrowing(value = "pointCutForServices()", throwing = "e")
public void afterThrowing(JoinPoint joinPoint, Exception e) {
	String name = joinPoint.getSignature().getName();
	System.out.println("afterThrowing---" + name + "----" + e.getMessage());
}

@Around(value = "pointCutForServices()")
public Object around(ProceedingJoinPoint pjp) throws Throwable {
	return pjp.proceed();
}
```

完整

```java
package com.a.bootweb.aop;

import org.aspectj.lang.JoinPoint;
import org.aspectj.lang.ProceedingJoinPoint;
import org.aspectj.lang.annotation.*;
import org.springframework.stereotype.Component;

/**
 * @author Corgile
 * @date 2022-02-26
 */
@Component
@Aspect
public class MyLogger {
	@Pointcut(value = "execution(* com.a.bootweb.service.*.*(..))")
	public void pointCutForServices() { }

	@Before(value = "pointCutForServices()")
	public void before(JoinPoint joinPoint) {
		String name = joinPoint.getSignature().getName();
		System.out.println("before-----" + name);
	}

	@After(value = "pointCutForServices()")
	public void after(JoinPoint joinPoint) {
		String name = joinPoint.getSignature().getName();
		System.out.println("after-----" + name);
	}

	@AfterReturning(value = "pointCutForServices()", returning = "result")
	public void afterReturning(JoinPoint joinPoint, Object result) {
		String name = joinPoint.getSignature().getName();
		System.out.println("afterReturning----" + name + "---" + result);
	}

	@AfterThrowing(value = "pointCutForServices()", throwing = "e")
	public void afterThrowing(JoinPoint joinPoint, Exception e) {
		String name = joinPoint.getSignature().getName();
		System.out.println("afterThrowing---" + name + "----" + e.getMessage());
	}

	@Around(value = "pointCutForServices()")
	public Object around(ProceedingJoinPoint pjp) throws Throwable {
		return pjp.proceed();
	}
}

```

## 文件上传

1.   全局异常处理大小超过限制

     ```java
     @ControllerAdvice
     public class GlobalController {
     
     	@ExceptionHandler(FileSizeLimitExceededException.class)
     	public void maxSizeFile(FileSizeLimitExceededException e, HttpServletResponse resopnse) {
     		resopnse.setContentType("text/html;charset=utf-8");
     		try {
     			PrintWriter out = resopnse.getWriter();
     			out.write("<h1>上传文件大小超过限制</h1>");
     			out.flush();
     			out.close();
     		} catch (IOException ioException) {
     			ioException.printStackTrace();
     		}
     	}
     }
     ```

     ![image-20220226230001340](https://gitee.com/corgile/images/raw/master/images/2021/image-20220226230001340.png)

2.   上传成功

     ![image-20220226230107670](https://gitee.com/corgile/images/raw/master/images/2021/image-20220226230107670.png)
     
     ```java
     package com.a.bootweb.controller;
     
     import org.springframework.web.bind.annotation.PostMapping;
     import org.springframework.web.bind.annotation.RequestMapping;
     import org.springframework.web.bind.annotation.RestController;
     import org.springframework.web.multipart.MultipartFile;
     
     import javax.servlet.http.HttpServletRequest;
     import java.io.File;
     import java.io.IOException;
     import java.text.SimpleDateFormat;
     import java.util.ArrayList;
     import java.util.Date;
     import java.util.List;
     import java.util.UUID;
     
     /**
      * @author Corgile
      * @date 2022-02-26
      */
     @RestController
     @RequestMapping(value = "file")
     public class FileUploadController {
     
     	@PostMapping(value = "upload")
     	public String upload(MultipartFile file, HttpServletRequest request) throws IOException {
     		String format = new SimpleDateFormat("/yyyy/MM-dd/").format(new Date());
     		String realPath = request.getServletContext().getRealPath("/img") + format;
     		File folder = new File(realPath);
     		if (!folder.exists()) {
     			folder.mkdirs();
     		}
     		return getUrl(request, format, folder, file);
     	}
     
     	@PostMapping(value = "uploads")
     	public List<String> uploads(MultipartFile[] files, HttpServletRequest request) throws IOException {
     		String format = new SimpleDateFormat("/yyyy/MM-dd/").format(new Date());
     		String realPath = request.getServletContext().getRealPath("/img") + format;
     		File folder = new File(realPath);
     		if (!folder.exists()) {
     			folder.mkdirs();
     		}
     		List<String> urls = new ArrayList<>();
     		for (MultipartFile file : files) {
     			urls.add(getUrl(request, format, folder, file));
     		}
     		urls.forEach(System.out::println);
     		return urls;
     	}
     
     	private String getUrl(HttpServletRequest request, String format, File folder, MultipartFile file) throws IOException {
     		String oldName = file.getOriginalFilename();
     		assert oldName != null;
     		String newName = UUID.randomUUID() + oldName.substring(oldName.lastIndexOf("."));
     		file.transferTo(new File(folder, newName));
     		return request.getScheme() + "://" + request.getServerName() + ":"
     				+ request.getServerPort() + "/img" + format + newName;
     	}
     
     }
     
     ```
     
3.   配合Ajax上传

     ```html
     <!DOCTYPE html>
     <html lang="en">
     <head>
     	<meta charset="UTF-8">
     	<title>文件上传</title>
     	<script src="jquery-3.2.1.js"></script>
     </head>
     <body>
     
     <form action="/file/upload" method="post" enctype="multipart/form-data">
     	<input type="file" name="file">
     	<input type="submit" value="表单上传">
     </form>
     
     <input type="file" id="file">
     <input type="button" value="Ajax单文件上传" onclick="upload()">
     <img alt="Ajax单文件上传" id="result">
     
     <form id="files" action="/file/uploads" method="post" enctype="multipart/form-data">
     	<input type="file" name="files" multiple>
     	<input type="submit" value="Ajax多文件上传">
     </form>
     <script>
     	function upload() {
     		let file = $("#file")[0].files[0];
     		let formData = new FormData();
     		formData.append("file", file);
     		$.ajax({
     			type: 'post',
     			url: '/file/upload',
     			processData: false,// 不用给我处理成对象
     			contentType: false,
     			data: formData,
     			success: function (res) {
     				$("#result").attr("src", JSON.parse(res))
     			}
     		})
     	}
     
     </script>
     </body>
     </html>
     ```

## 整合持久层

### JDBCTemplate + 多数据源

1.   配置文件中说明要用到的数据库

     ![image-20220227032532117](https://gitee.com/corgile/images/raw/master/images/2021/image-20220227032532117.png)

2.   手动配置数据源

     ![image-20220227032626406](https://gitee.com/corgile/images/raw/master/images/2021/image-20220227032626406.png)

3.   数据源的操作类

     ![image-20220227032709378](https://gitee.com/corgile/images/raw/master/images/2021/image-20220227032709378.png)

4.   在Service中指明用的是哪一个数据源的操作类

     ![image-20220227032834164](https://gitee.com/corgile/images/raw/master/images/2021/image-20220227032834164.png)
     
5.   测试通过✅

     ![image-20220227033128695](https://gitee.com/corgile/images/raw/master/images/2021/image-20220227033128695.png)

### MyBatis + 多数据源

>   与Jdbc多数据源配置类似，`DataSourceConfig`类不变

1.   properties文件

     ![image-20220227161821778](https://gitee.com/corgile/images/raw/master/images/2021/image-20220227161821778.png)

2.   添加各个数据源的配置类，这里只给出其一，要加`@Primary` 

     ![image-20220227162014677](https://gitee.com/corgile/images/raw/master/images/2021/image-20220227162014677.png)

3.   创建数据访问接口和对应的xml文件

     ![image-20220227162342377](https://gitee.com/corgile/images/raw/master/images/2021/image-20220227162342377.png)

4.   测试✅

     ![image-20220227162610897](https://gitee.com/corgile/images/raw/master/images/2021/image-20220227162610897.png)

### JPA（Java Persistence API）

1.   配置JPA相关

     ![image-20220227172221966](https://gitee.com/corgile/images/raw/master/images/2021/image-20220227172221966.png)

2.   创建一个实体类

     ![image-20220227172437085](https://gitee.com/corgile/images/raw/master/images/2021/image-20220227172437085.png)

3.   启动项目，表已被自动创建

     ![image-20220227172641728](https://gitee.com/corgile/images/raw/master/images/2021/image-20220227172641728.png)

4.   随便弄几个函数查询

     ![image-20220227181000171](https://gitee.com/corgile/images/raw/master/images/2021/image-20220227181000171.png)

     -   Controller

     ![image-20220227181041348](https://gitee.com/corgile/images/raw/master/images/2021/image-20220227181041348.png)

     -   测试通过✅

     ![image-20220227181207044](https://gitee.com/corgile/images/raw/master/images/2021/image-20220227181207044.png)

## Session共享

正向代理：Proxy向Client作出response，并隐藏Server袭击

反向代理：Proxy向Server发出request，并隐藏Client细节

负载均衡

```java
# 上有服务器配置
upstream some_server_name{
    server 127.0.0.1:8080 weight=2;
    server 127.0.0.1:8081 weight=1;
}
# 路由分发配置
server {
    listen	80;
    server_name	localhost;
    location / {
        proxy_pass	http://some_server_name;
        proxy_redirect	default;
    }
}
```

## JdbcTemplate 构建 Restful