工作笔记

最新推荐文章于 2021-09-19 21:00:26 发布

槐夏十八

最新推荐文章于 2021-09-19 21:00:26 发布

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分类专栏：工作文章标签： Java

本文链接：https://blog.youkuaiyun.com/Bii_yu/article/details/80182502

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重点：戒骄戒躁！！！写任何功能的时候都要先梳理逻辑！！！不然很容易重写，浪费时间！！！

1.xxx cannot be resolved to a type

解决方法：Project ——> Clean——>选择要clean的项目。

2.Java访问接口

		// 请求体
		Map<String, String> requestBody = new HashMap<String, String>();
		requestBody.put("sentpair", rdssList.toString());
		String result = "";
		// POST请求
		HttpPost requestMethod = new HttpPost(
				url地址);
		// 添加默认请求头
		requestMethod.addHeader("Connection", "keep-alive");
		requestMethod.addHeader("Pragma", "no-cache");
		requestMethod
				.addHeader(
						"Accept",
						"text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8");
		requestMethod.addHeader("Accept-Encoding", "gzip, deflate");
		requestMethod.addHeader("Accept-Language",
				"en-US,en;q=0.9,zh-CN;q=0.8,zh;q=0.7");
		// 封装请求体
		Iterator<Map.Entry<String, String>> iterator = requestBody.entrySet()
				.iterator();
		List<BasicNameValuePair> nameValuePairList = new ArrayList<BasicNameValuePair>();
		while (iterator.hasNext()) {
			Map.Entry<String, String> entry = iterator.next();
			String name = entry.getKey();
			String value = entry.getValue();
			BasicNameValuePair nameValuePair = new BasicNameValuePair(name,
					value);
			nameValuePairList.add(nameValuePair);
		}

		try {
			UrlEncodedFormEntity entity = new UrlEncodedFormEntity(
					nameValuePairList, "UTF-8");
			requestMethod.setEntity(entity);
			InputStream is = null;
			InputStreamReader isr = null;
			BufferedReader reader = null;
			RequestConfig config = RequestConfig.custom()
					.setConnectTimeout(300000)
					.setConnectionRequestTimeout(300000)
					.setSocketTimeout(300000).build();
			CloseableHttpClient httpClient = HttpClientBuilder.create()
					.setDefaultRequestConfig(config).build();

			CloseableHttpResponse response = null;
			StringBuffer stringBuffer = new StringBuffer();
			try {
				try {
					response = httpClient.execute(requestMethod);
				} catch (ClientProtocolException e1) {
					// TODO Auto-generated catch block
					e1.printStackTrace();
				} catch (IOException e1) {
					// TODO Auto-generated catch block
					e1.printStackTrace();
				}
				try {
					is = response.getEntity().getContent();
				} catch (IOException e1) {
					// TODO Auto-generated catch block
					e1.printStackTrace();
				}
				isr = new InputStreamReader(is);
				reader = new BufferedReader(isr);
				String inputLine = StringUtils.EMPTY;
				try {
					while (null != (inputLine = reader.readLine())) {
						stringBuffer.append(inputLine);
					}
				} catch (IOException e) {
					// TODO Auto-generated catch block
					e.printStackTrace();
				}
			} finally {
				IOUtils.closeQuietly(reader);
				IOUtils.closeQuietly(httpClient);
				IOUtils.closeQuietly(isr);
				IOUtils.closeQuietly(response);
			}
			result = stringBuffer.toString();
			resultJson.put("result", result);
		} catch (UnsupportedEncodingException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}

3.前后台分离，后端向前端传文件



import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.OutputStream;
import java.io.UnsupportedEncodingException;
import java.net.URLDecoder;
import java.net.URLEncoder;
import java.util.Map;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.commons.io.IOUtils;
import org.apache.commons.lang.StringUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;

public class DownloadYhsc extends HttpServlet {

	/**
	 * @author admin
	 * @version 2.0
	 */
	private static final long serialVersionUID = 8529206527876956262L;

	final protected static Logger logger = LoggerFactory
			.getLogger(Download.class);

	@Autowired
	private ExportExcelUtil exportExcelUtil;

	/**
	 * The doGet method of the servlet. <br>
	 * 
	 * This method is called when a form has its tag value method equals to get.
	 * 
	 * @param request
	 *            the request send by the client to the server
	 * @param response
	 *            the response send by the server to the client
	 * @throws ServletException
	 *             if an error occurred
	 * @throws IOException
	 *             if an error occurred
	 */
	@Override
	@SuppressWarnings({ "unchecked" })
	public void doGet(HttpServletRequest request, HttpServletResponse response) {
		Map<String, Object> paramMap = request.getParameterMap();
		if (null == paramMap || paramMap.isEmpty()) {
			return;
		}

		String serverPath = new StringBuilder()
				.append(ArteryUtil.getRequest().getSession()
						.getServletContext().getRealPath(File.separator))
				.append("pub\\yhsc").append(File.separator).toString();

		String fileName;
		try {
			fileName = URLEncoder.encode("xxx.docx", "UTF-8");
			String header = new StringBuilder().append("attachment;filename=")
					.append(fileName).toString();
			response.setContentType("application/octet-stream");
			response.addHeader("Content-disposition", header);
			response.addHeader("Transfer-Encoding", null);
			response.addHeader("connection", "close");
		} catch (UnsupportedEncodingException e1) {
			// TODO Auto-generated catch block
			e1.printStackTrace();
		}

		File file = new File(serverPath + "xxx.docx");
		FileInputStream in = null;
		OutputStream out = null;
		try {
			in = new FileInputStream(file);
			out = response.getOutputStream();
			IOUtils.copy(in, out);
			out.flush();
		} catch (FileNotFoundException e) {
			e.printStackTrace();
			logger.error("文件不存在" + e);
		} catch (IOException e) {
			e.printStackTrace();
			logger.error("获取流异常" + e);
		} finally {
			IOUtils.closeQuietly(out);
			IOUtils.closeQuietly(in);
		}
	}

	/**
	 * 转换编码
	 * 
	 * @param fileName
	 * @return
	 */
	private String getDecodedStr(String str) {
		String decodedStr = null;
		try {
			if (null == str || str.isEmpty()) {
				decodedStr = StringUtils.EMPTY;
			} else {
				decodedStr = URLDecoder.decode(str, "UTF-8");
			}
		} catch (UnsupportedEncodingException e) {
			e.printStackTrace();
			logger.error("不支持的编码" + e);
		}
		return decodedStr;
	}

	/**
	 * Destruction of the servlet. <br>
	 */
	@Override
	public void destroy() {
		super.destroy(); // Just puts "destroy" string in log
		// Put your code here
	}

	/**
	 * Initialization of the servlet. <br>
	 * 
	 * @throws ServletException
	 *             if an error occurs
	 */
	@Override
	public void init() throws ServletException {
		// Put your code here
	}

	/**
	 * The doPost method of the servlet. <br>
	 * 
	 * This method is called when a form has its tag value method equals to
	 * post.
	 * 
	 * @param request
	 *            the request send by the client to the server
	 * @param response
	 *            the response send by the server to the client
	 * @throws ServletException
	 *             if an error occurred
	 * @throws IOException
	 *             if an error occurred
	 */
	@Override
	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		doGet(request, response);
	}
}

4.对map的value进行排序

		// 对map的value进行排序
		List<Map.Entry<String, String>> list = new ArrayList<Map.Entry<String, String>>(
				XzcfMap.entrySet());
		Collections.sort(list, new Comparator<Map.Entry<String, String>>() {
			// 升序排序
			public int compare(Entry<String, String> o1,
					Entry<String, String> o2) {
				return o1.getValue().compareTo(o2.getValue());
			}

		});

5.在循环里产生相同的UUID问题

解决：查看保存UUID的值是不是全局变量！！！

6.TreeMap倒序

		TreeMap<String, String> map = new TreeMap<String, String>(
				new Comparator<String>() {
					public int compare(String o1, String o2) {
						return o2.compareTo(o1);
					}
				});

7.MyBatis批量增删改查

	<!-- 批量增加 -->  
    <insert id="insertUsersBatch" parameterType="java.util.List">  
        insert into user(userName,password) values  
        <foreach collection="list" item="item" index="index" separator=",">  
            (#{item.userName},#{item.password})  
        </foreach>  
    </insert>  
	<!-- 批量删除 -->  
    <delete id="deleteUsersBatch" parameterType="java.util.List">  
        delete from user where id in  
        <foreach collection="list" index="index" item="item" open="(" close=")" separator=",">  
            #{item}  
        </foreach>  
    </delete>  
	<!-- 批量查询 -->  
    <select id="selectUsersBatch" resultType="User">  
        select *  
        from user where id in  
        <foreach collection="list" index="index" item="item" open="(" separator="," close=")">  
        #{item}  
        </foreach>  
    </select>  
	<!-- 批量更新 --> 
	<update id="updateUsersBatch" parameterType="java.util.List">  
        <foreach collection="list" item="item" index="index" open="begin" close=";end;" separator=";" >   
            update user   
            <set>         
                userName = #{item.userName}, password = #{item.password}  
            </set>  
            where id = #{item.id}  
        </foreach>  
    </update>

8.MyBatis写SQL的大于等于和小于等于

大于等于：<![CDATA[>=]]>

小于等于：<![CDATA[<=]]>

9.日期加一天的方法

Date time = new Date();
Calendar c = Calendar.getInstance();
c.setTime(time);
c.add(Calendar.DAY_OF_MONTH, 1)

10.PostgreSQL传时间类型

不能传String类型，会报错。

报错信息：timestamp without timeZone（时间戳没有时区）

11.jar包冲突解决方法

1.在maven的jar包中找到对应的jar包

2.在pom文件查看Dependency Hierarchy

3.看jar包版本信息是否对应

4.在项目的pom文件中找到依赖

5.右键Exclude Maven Artifact，保存

6.更新Maven依赖（项目右键update dependency）

12.前端开发：点击事件返回页面顶部

<!-- 定义一个名称为top的锚点链接 -->

<a name="top"></a>

<!-- 这里是网页主体内容，此处省略 -->


<!-- 返回页面顶部top锚点的链接 -->
<a href="#top">返回顶部</a>

13.前端开发：弹出框点击弹出框以外的地方，收起弹出框

:close-on-click-modal="true"

14.前端开发：VUE规定V-FOR循环次数

<p v-for="(lab,index) in Options" v-if='index<=1'></p>

15.JSON转换出现错误:net.sf.json.JSONException: Unterminated string at character

出现原因：字符串中存在换行符，导致json转换异常

解决方法：去除字符串中的换行符

代码：

"字符串".replaceAll("[\b\r\n\t]*", "")

16.where和having的区别

WHERE语句在GROUPBY语句之前；SQL会在分组之前计算WHERE语句。
HAVING语句在GROUPBY语句之后；SQL会在分组之后计算HAVING语句。

having是对group by后的结果进行筛选，可以写函数

17.Triple抽象类，实现这个抽象类的类能够存储三个对象

忘了就百度！！！