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Java开发中常用记录

福牛 5月 07, 2023 23 0

一、编程式事务

1.在执行事务提交或者回滚之前，事务状态不确定时，可以判断一下事务是否已完成，避免重复提交或者回滚出现异常

举例：

  1. TransactionStatus transactionStatus = platformTransactionManager.getTransaction(transactionDefinition);
  2. if (!transactionStatus.isCompleted()) {
  3.      platformTransactionManager.commit(transactionStatus);
  4. }

2.由于编程式事务不会自动提交或者回滚，我们可以在try-catch之后加一个finally，判断事务未完成时，进行回滚，保证每个事务一定会结束

举例：

  1. TransactionStatus transactionStatus = platformTransactionManager.getTransaction(transactionDefinition);
  2. try {
  3.      … …
  4. } catch (Exception ex) {
  5.      … …
  6. } finally {
  7.      if (!transactionStatus.isCompleted()) {
  8.          platformTransactionManager.rollback(transactionStatus);
  9.      }
  10. }

二、Stream

1.使用到的数据结构及模拟数据

  1. import io.swagger.annotations.ApiModelProperty;
  2. import lombok.Data;
  3. import Java.math.BigDecimal;
  4. @Data
  5. public class Student {
  6.      @ApiModelProperty(value = “学生ID”)
  7.      private String studentId;
  8.      @ApiModelProperty(value = “学生姓名”)
  9.      private String studentName;
  10.      @ApiModelProperty(value = “学生性别，1-男，2-女”)
  11.      private String studentSex;
  12.      @ApiModelProperty(value = “学生年龄Integer”)
  13.      private Integer studentAgeInt;
  14.      @ApiModelProperty(value = “学生年龄Double”)
  15.      private Double studentAgeDou;
  16.      @ApiModelProperty(value = “学生年龄BigDecimal”)
  17.      private BigDecimal studentAgeDec;
  18. }
  1. // 数据列表 List
  2. List<Student> studentList = new ArrayList<>();
  3. Student student = new Student();
  4. student.setStudentId(“20220930000001”);
  5. student.setStudentName(“赵甲”);
  6. student.setStudentSex(“1”);
  7. student.setStudentAgeInt(11);
  8. student.setStudentAgeDou(11.11);
  9. student.setStudentAgeDec(new BigDecimal(11.11));
  10. studentList.add(student);
  11. student = new Student();
  12. student.setStudentId(“20220930000002”);
  13. student.setStudentName(“钱乙”);
  14. student.setStudentSex(“2”);
  15. student.setStudentAgeInt(12);
  16. student.setStudentAgeDou(12.12);
  17. student.setStudentAgeDec(new BigDecimal(12.12));
  18. studentList.add(student);
  19. student = new Student();
  20. student.setStudentId(“20220930000003”);
  21. student.setStudentName(“孙丙”);
  22. student.setStudentSex(“1”);
  23. student.setStudentAgeInt(13);
  24. student.setStudentAgeDou(13.13);
  25. student.setStudentAgeDec(new BigDecimal(13.13));
  26. studentList.add(student);
  27. student = new Student();
  28. student.setStudentId(“20220930000004”);
  29. student.setStudentName(“李丁”);
  30. student.setStudentSex(“2”);
  31. student.setStudentAgeInt(14);
  32. student.setStudentAgeDou(14.14);
  33. student.setStudentAgeDec(new BigDecimal(14.14));
  34. studentList.add(student);
  35. student = new Student();
  36. student.setStudentId(“20220930000005”);
  37. student.setStudentName(“周戊”);
  38. student.setStudentSex(“1”);
  39. student.setStudentAgeInt(15);
  40. student.setStudentAgeDou(15.15);
  41. student.setStudentAgeDec(new BigDecimal(15.15));
  42. studentList.add(student);
  1. // 数据Map
  2. Map<String,Student> studentMap = new HashMap<>(5);
  3. Student student = new Student();
  4. student.setStudentId(“20220930000001”);
  5. student.setStudentName(“赵甲”);
  6. student.setStudentSex(“1”);
  7. student.setStudentAgeInt(11);
  8. student.setStudentAgeDou(11.11);
  9. student.setStudentAgeDec(new BigDecimal(11.11));
  10. studentMap.put(student.getStudentId(),student);
  11. student = new Student();
  12. student.setStudentId(“20220930000002”);
  13. student.setStudentName(“钱乙”);
  14. student.setStudentSex(“2”);
  15. student.setStudentAgeInt(12);
  16. student.setStudentAgeDou(12.12);
  17. student.setStudentAgeDec(new BigDecimal(12.12));
  18. studentMap.put(student.getStudentId(),student);
  19. student = new Student();
  20. student.setStudentId(“20220930000003”);
  21. student.setStudentName(“孙丙”);
  22. student.setStudentSex(“1”);
  23. student.setStudentAgeInt(13);
  24. student.setStudentAgeDou(13.13);
  25. student.setStudentAgeDec(new BigDecimal(13.13));
  26. studentMap.put(student.getStudentId(),student);
  27. student = new Student();
  28. student.setStudentId(“20220930000004”);
  29. student.setStudentName(“李丁”);
  30. student.setStudentSex(“2”);
  31. student.setStudentAgeInt(14);
  32. student.setStudentAgeDou(14.14);
  33. student.setStudentAgeDec(new BigDecimal(14.14));
  34. studentMap.put(student.getStudentId(),student);
  35. student = new Student();
  36. student.setStudentId(“20220930000005”);
  37. student.setStudentName(“周戊”);
  38. student.setStudentSex(“1”);
  39. student.setStudentAgeInt(15);
  40. student.setStudentAgeDou(15.15);
  41. student.setStudentAgeDec(new BigDecimal(15.15));
  42. studentMap.put(student.getStudentId(),student);

2.过滤-filter

  1. // 过滤所有女生
  2. List<Student> studentListT = studentList.stream()
  3.          .filter(item -> “2”.equals(item.getStudentSex())).collect(Collectors.toList());
  4. // 过滤12岁以上学生（3种数据类型示例）
  5. studentListT = studentList.stream().filter(item –> item.getStudentAgeInt() > 12).collect(Collectors.toList());
  6. studentListT = studentList.stream().filter(item -> item.getStudentAgeDou() > 12).collect(Collectors.toList());
  7. studentListT = studentList.stream()
  8.          .filter(item -> item.getStudentAgeDec().compareTo(new BigDecimal(12)) > 0).collect(Collectors.toList());
  9. // 过滤12岁以上男生（2种方法示例）
  10. studentListT = studentList.stream().filter(item -> “1”.equals(item.getStudentSex()))
  11.          .filter(item -> item.getStudentAgeInt() &gt; 12).collect(Collectors.toList());
  12. studentListT = studentList.stream()
  13.          .filter(item -> “1”.equals(item.getStudentSex()) && item.getStudentAgeInt() > 12).collect(Collectors.toList());

三、Map转对象

最近，研究map与java对象之间的相互转换，总结了5种方法

https://www.jb51.net/article/190478.htm

四、linux常用命令

1.查看所有java进程

ps -ef | grep java

2.结束某个进程

kill -9 pid

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