Java笔记(2020)

1. 复杂JSON字符串转模型

1 import com.fasterxml.jackson.core.type.TypeReference;
2 import com.fasterxml.jackson.databind.ObjectMapper;
1 ObjectMapper mapper = new ObjectMapper();
2 List<CustomModel> list =  mapper.readValue(json, new TypeReference<List<CustomModel>>() { });

 

2. 在非Bean对象调用Spring Bean管理的对象

 1 package com.wunaozai.demo
 2 
 3 import org.springframework.beans.BeansException;
 4 import org.springframework.context.ApplicationContext;
 5 import org.springframework.context.ApplicationContextAware;
 6 import org.springframework.stereotype.Component;
 7 
 8 /**
 9  * 为不是spring所管理的对象,需要引用spring管理对象的时候所用的工具类
10  * @author wunaozai
11  *
12  */
13 @Component
14 public class SpringApplicationContext implements ApplicationContextAware {
15 
16     protected static ApplicationContext context;
17     
18     @Override
19     public void setApplicationContext(ApplicationContext ctx) throws BeansException {
20         context = (ApplicationContext) ctx;
21     }
22 
23     public static ApplicationContext getContext(){
24         return context;
25     }
26     
27 }

调用

1 CustomerService influxdbconnectService = SpringApplicationContext.getContext().getBean(CustomerService.class);

 

3. Spring Boot 项目出现 pom.xml 第一行莫名的错误，在pom.xml 的 properties段下增加

1 <maven-jar-plugin.version>3.0.0</maven-jar-plugin.version>

 

4. eclipse maven 更换 阿里源， 需要配置 settings.xml 文件

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <settings>
 3     <mirrors>
 4         <mirror>
 5             <id>alimaven</id>
 6             <name>aliyun maven</name>
 7             <url>http://maven.aliyun.com/nexus/content/groups/public/</url>
 8             <mirrorOf>central</mirrorOf>
 9         </mirror>
10     </mirrors>
11   <profiles>
12     <profile>
13        <id>nexus</id>
14         <repositories>
15             <repository>
16                 <id>nexus</id>
17                 <name>local private nexus</name>
18                 <url>http://maven.oschina.net/content/groups/public/</url>
19                 <releases>
20                     <enabled>true</enabled>
21                 </releases>
22                 <snapshots>
23                     <enabled>false</enabled>
24                 </snapshots>
25             </repository>
26         </repositories>
27          
28         <pluginRepositories>
29             <pluginRepository>
30             <id>nexus</id>
31             <name>local private nexus</name>
32             <url>http://maven.oschina.net/content/groups/public/</url>
33             <releases>
34                 <enabled>true</enabled>
35             </releases>
36             <snapshots>
37                 <enabled>false</enabled>
38             </snapshots>
39             </pluginRepository>
40         </pluginRepositories>
41     </profile></profiles>
42 </settings>

 

5. spring boot 项目，用maven编译打包时，使用wrapper时遇到下载apache-maven失败，可以到 .m2/wrapper/dists/apache-maven-** 目录下，将离线包放到该目录下。或者修改wrapper目录下的maven-wrapper.properties文件里面的distributionUrl 为本地离线地址，都是可以的。

 

6. mybatis-plus 打印SQL详细日志，在application配置文件中增加

1 #mybatis-plus
2 mybatis-plus.mapper-locations=classpath:com/wunaozai/demo/mapper/*.xml
3 mybatis-plus.configuration.log-impl=org.apache.ibatis.logging.stdout.StdOutImpl

 

 7. springboot中默认使用jackson做json序列化和反序列化，后台接收数据时将上述日期字符串转成LocalDateTime时，会报如下错误

JSON parse error: Cannot deserialize value of type java.time.LocalDateTime from String “2018-09-20 08:01:00”: Failed to deserialize java.time.LocalDateTime: (java.time.format.DateTimeParseException) Text ‘2018-09-20 08:01:00’ could not be parsed at index 10; nested exception is com.fasterxml.jackson.databind.exc.InvalidFormatException: Cannot deserialize value of type java.time.LocalDateTime from String “2018-09-20 08:01:00”: Failed to deserialize java.time.LocalDateTime: (java.time.format.DateTimeParseException) Text ‘2018-09-20 08:01:00’ could not be parsed at index 10

解决办法：

导入jackson-datatype

1         <dependency>
2             <groupId>com.fasterxml.jackson.datatype</groupId>
3             <artifactId>jackson-datatype-jsr310</artifactId>
4         </dependency>

配置bean

 1     @Bean
 2     public ObjectMapper serializingObjectMapper() {
 3         JavaTimeModule module = new JavaTimeModule();
 4         LocalDateTimeDeserializer deserializer =
 5                 new LocalDateTimeDeserializer(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss"));
 6         module.addDeserializer(LocalDateTime.class, deserializer);
 7         ObjectMapper object = Jackson2ObjectMapperBuilder.json()
 8                 .modules(module)
 9                 .featuresToDisable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS)
10                 .build();
11         return object;
12     }

 

8. PCM 转 WAV 格式

　　PcmToWav.java

 1 package com.wunaozai.demo.pcm2wav;
 2 
 3 import java.io.FileInputStream;
 4 import java.io.FileOutputStream;
 5 import java.io.IOException;
 6 
 7 /**
 8  * PCM 转 WAV
 9  * @author wunaozai
10  * @Date 2020-11-03
11  */
12 public class PcmToWav {
13     public static void main(String[] args) throws Exception {
14         convertAudioFiles("F:\\voice\\1311458187862568961.pcm", "F:\\voice\\1311458187862568961.pcm.mp3");
15     }
16     
17     public static void convertAudioFiles(String src, String dest) throws IOException {
18         FileInputStream fis = new FileInputStream(src);
19         FileOutputStream fos = new FileOutputStream(dest);
20         //计算长度
21         byte[] buf = new byte[1024 * 4];
22         int size = fis.read(buf);
23         int PCMSize = 0;
24         while (size != -1) {
25             PCMSize += size;
26             size = fis.read(buf);
27         }
28         fis.close();
29  
30         //填入参数，比特率等等。这里用的是16位单声道 8000 hz
31         WaveHeader header = new WaveHeader();
32         //长度字段 = 内容的大小（PCMSize) + 头部字段的大小(不包括前面4字节的标识符RIFF以及fileLength本身的4字节)
33         header.fileLength = PCMSize + (44 - 8);
34         header.FmtHdrLeth = 16;
35         header.BitsPerSample = 16;
36         header.Channels = 1;
37         header.FormatTag = 0x0001;
38         header.SamplesPerSec = 16000;
39         header.BlockAlign = (short) (header.Channels * header.BitsPerSample / 8);
40         header.AvgBytesPerSec = header.BlockAlign * header.SamplesPerSec;
41         header.DataHdrLeth = PCMSize;
42  
43         byte[] h = header.getHeader();
44  
45         assert h.length == 44; //WAV标准，头部应该是44字节
46         // write header
47         fos.write(h, 0, h.length);
48         // write data stream
49         fis = new FileInputStream(src);
50         size = fis.read(buf);
51         while (size != -1) {
52             fos.write(buf, 0, size);
53             size = fis.read(buf);
54         }
55         fis.close();
56         fos.close();
57         System.out.println("Convert OK!");
58     }
59 }
View Code

　　WaveHeader.java

 1 package com.wunaozai.demo.pcm2wav;
 2 
 3 import java.io.ByteArrayOutputStream;
 4 import java.io.IOException;
 5 
 6 /**
 7  * Wav头
 8  * @author wunaozai
 9  * @Date 2020-11-03
10  */
11 public class WaveHeader {
12     public final char fileID[] = {'R', 'I', 'F', 'F'};
13     public int fileLength;
14     public char wavTag[] = {'W', 'A', 'V', 'E'};
15     public char FmtHdrID[] = {'f', 'm', 't', ' '};
16     public int FmtHdrLeth;
17     public short FormatTag;
18     public short Channels;
19     public int SamplesPerSec;
20     public int AvgBytesPerSec;
21     public short BlockAlign;
22     public short BitsPerSample;
23     public char DataHdrID[] = {'d', 'a', 't', 'a'};
24     public int DataHdrLeth;
25  
26     public byte[] getHeader() throws IOException {
27         ByteArrayOutputStream bos = new ByteArrayOutputStream();
28         WriteChar(bos, fileID);
29         WriteInt(bos, fileLength);
30         WriteChar(bos, wavTag);
31         WriteChar(bos, FmtHdrID);
32         WriteInt(bos, FmtHdrLeth);
33         WriteShort(bos, FormatTag);
34         WriteShort(bos, Channels);
35         WriteInt(bos, SamplesPerSec);
36         WriteInt(bos, AvgBytesPerSec);
37         WriteShort(bos, BlockAlign);
38         WriteShort(bos, BitsPerSample);
39         WriteChar(bos, DataHdrID);
40         WriteInt(bos, DataHdrLeth);
41         bos.flush();
42         byte[] r = bos.toByteArray();
43         bos.close();
44         return r;
45     }
46     private void WriteShort(ByteArrayOutputStream bos, int s) throws IOException {
47         byte[] mybyte = new byte[2];
48         mybyte[1] = (byte) ((s << 16) >> 24);
49         mybyte[0] = (byte) ((s << 24) >> 24);
50         bos.write(mybyte);
51     }
52     private void WriteInt(ByteArrayOutputStream bos, int n) throws IOException {
53         byte[] buf = new byte[4];
54         buf[3] = (byte) (n >> 24);
55         buf[2] = (byte) ((n << 8) >> 24);
56         buf[1] = (byte) ((n << 16) >> 24);
57         buf[0] = (byte) ((n << 24) >> 24);
58         bos.write(buf);
59     }
60     private void WriteChar(ByteArrayOutputStream bos, char[] id) {
61         for (char c : id) {
62             bos.write(c);
63         }
64     }
65 }
View Code

 

9. Java 线程池简单使用

  1 package com.wunaozai.demo.testdemo;
  2 
  3 import java.util.ArrayList;
  4 import java.util.List;
  5 import java.util.concurrent.Callable;
  6 import java.util.concurrent.ExecutionException;
  7 import java.util.concurrent.ExecutorService;
  8 import java.util.concurrent.Executors;
  9 import java.util.concurrent.Future;
 10 import java.util.concurrent.ScheduledExecutorService;
 11 import java.util.concurrent.ThreadPoolExecutor;
 12 import java.util.concurrent.TimeUnit;
 13 
 14 /**
 15  * 测试线程池
 16  * @author wunaozai
 17  * @Date 2020-12-09
 18  */
 19 public class TestThreadPoolExecutor {
 20 
 21     public static void main(String[] args) {
 22         //testSingleThreadPool();
 23         //testFixedThreadPool();
 24         //testCachedThreadPool();
 25         //testScheduledThreadPool();
 26         //testAwaitTermination();
 27         testThreadPoolResult();
 28     }
 29     
 30     //创建单个线程的线程池
 31     public static void testSingleThreadPool() {
 32         ExecutorService service = Executors.newSingleThreadExecutor();
 33         for(int i=0; i<10; i++) {
 34             service.submit(newRunnable());
 35         }
 36         service.shutdown(); //禁止再继续提交任务，等所有任务都执行完成后，关闭当前线程池
 37         //service.shutdownNow(); //禁止再提交任务，不等所有任务执行完，立即关闭当前线程池
 38         System.out.println("结束");
 39     }
 40     //创建使用固定线程数的线程池
 41     public static void testFixedThreadPool() {
 42         ExecutorService service = Executors.newFixedThreadPool(3);
 43         for(int i=0; i<10; i++) {
 44             service.submit(newRunnable());
 45         }
 46         service.shutdown();
 47         System.out.println("结束");
 48     }
 49     //创建一个根据需要动态创建新线程的线程池
 50     public static void testCachedThreadPool() {
 51         ExecutorService service = Executors.newCachedThreadPool();
 52         for(int i=0; i<200; i++) {
 53             service.submit(newRunnable());
 54         }
 55         service.shutdown();
 56         System.out.println("结束");
 57     }
 58     //创建使用固定线程数的定时任务线程池
 59     public static void testScheduledThreadPool() {
 60         ScheduledExecutorService service = Executors.newScheduledThreadPool(5);
 61         for(int i=0; i<20; i++) {
 62             service.schedule(newRunnable(), 3, TimeUnit.SECONDS);
 63         }
 64         service.shutdown();
 65         System.out.println("结束");
 66     }
 67     //阻塞式，等待线程池关闭
 68     public static void testAwaitTermination() {
 69         ScheduledExecutorService service = Executors.newSingleThreadScheduledExecutor();
 70         service.schedule(newRunnable(), 2, TimeUnit.SECONDS);
 71         try {
 72             boolean flag = service.awaitTermination(4, TimeUnit.SECONDS);
 73             if(flag == false) {
 74                 service.shutdown();
 75             }
 76         } catch (InterruptedException e) {
 77             e.printStackTrace();
 78         }
 79         System.out.println("结束");
 80     }
 81     
 82     private static Runnable newRunnable() {
 83         return new Runnable() {
 84             @Override
 85             public void run() {
 86                 try {
 87                     Thread.sleep(200);
 88                 } catch (InterruptedException e) {
 89                     e.printStackTrace();
 90                 }
 91                 System.out.println(Thread.currentThread().getName() + "正在执行");
 92             }
 93         };
 94     }
 95     
 96     //测试带返回值的线程池
 97     public static void testThreadPoolResult() {
 98         ThreadPoolExecutor service = (ThreadPoolExecutor) Executors.newFixedThreadPool(3);
 99         
100         List<Future<String>> resultList = new ArrayList<>();
101         for(int i=0; i<10; i++) {
102             Future<String> ret = service.submit(newCallable("val: " + i)); //异步提交
103             resultList.add(ret);
104         }
105         
106         //同步取值
107         while(service.getCompletedTaskCount() < resultList.size()) {
108             System.out.println("当前完成数: " + service.getCompletedTaskCount());
109             for(int i=0; i<resultList.size(); i++) {
110                 Future<String> ret = resultList.get(i);
111                 System.out.printf("Task %d: %s\n", i, ret.isDone());
112             }
113             try {
114                 Thread.sleep(50);
115             } catch (InterruptedException e) {
116                 e.printStackTrace();
117             }
118         }
119         //所有线程都返回结果
120         for(int i=0; i<resultList.size(); i++) {
121             Future<String> result = resultList.get(i);
122             String ret = "Err";
123             try {
124                 ret = result.get(); //阻塞读取
125             } catch (InterruptedException | ExecutionException e) {
126                 e.printStackTrace();
127             }
128             System.out.printf("Task: %d, result %s\n", i, ret);
129         }
130         service.shutdown();
131         System.out.println("结束");
132     }
133     
134     public static Callable<String> newCallable(String txt) {
135         return new Callable<String>() {
136             @Override
137             public String call() throws Exception {
138                 System.out.println(Thread.currentThread().getName() + "正在执行");
139                 Thread.sleep(200);
140                 return txt;
141             }
142         };
143     }
144 
145 }

 

10. Mybatis-Plus 自定义SQL

1 @EnableTransactionManagement(proxyTargetClass = true) //开启事务

Mapper.java

1 public interface Mapper {
2 
3     public List<Model> selectList(@Param(value=Constants.WRAPPER) Wrapper<?> wrapper);
4 
5     public IPage<Model> selectPage(@Param(value="page") IPage<?> page,
6             @Param(value=Constants.WRAPPER) Wrapper<?> wrapper);
7 }

Mapper.xml

 1 <?xml version="1.0" encoding="UTF-8" ?>
 2 <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
 3 <mapper namespace="com.wunaozai.mapper.Mapper">
 4 
 5     <select id="selectList" resultType="com.wunaozai.model.Model">
 6         SELECT * FROM tbl ${ew.customSqlSegment}
 7     </select>
 8     
 9     <select id="selectPage" resultType="com.wunaozai.model.Model">
10         SELECT * FROM tbl ${ew.customSqlSegment}
11     </select>
12 </mapper>

 11. 清理Postgres表空间

1 # 查询所有表占用空间
2 select relname, pg_size_pretty(pg_relation_size(relid)) as size from pg_stat_user_tables;
3 # 针对已经delete的表进行vacuum full
4 vacuum FULL device_event_log ;

 

 

持续更新...

posted @ 2020-01-10 10:46  无脑仔的小明  阅读(537)  评论(0)  编辑  收藏  举报