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Java开发中常用记录

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：

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TransactionStatus transactionStatus =  platformTransactionManager.getTransaction(transactionDefinition);

if (!transactionStatus.isCompleted()) {

     platformTransactionManager测试数据mit(transactionStatus);

}

 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：

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TransactionStatus transactionStatus = platformTransactionManager.getTransaction(transactionDefinition);

try {

     ... ...

} catch (Exception ex) {

     ... ...

} finally {

     if (!transactionStatus.isCompleted()) {

         platformTransactionManager.rollback(transactionStatus);

     }

}

二、Stream

1.使用到的数据结构及模拟数据

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import io.swagger.annotations.ApiModelProperty;

import lombok.Data;

import java.math.BigDecimal;

@Data

public class Student {

     @ApiModelProperty (value = "学生ID" )

     private String studentId;

     @ApiModelProperty (value = "学生姓名" )

     private String studentName;

     @ApiModelProperty (value = "学生性别，1-男，2-女" )

     private String studentSex;

     @ApiModelProperty (value = "学生年龄Integer" )

     private Integer studentAgeInt;

     @ApiModelProperty (value = "学生年龄Double" )

     private Double studentAgeDou;

     @ApiModelProperty (value = "学生年龄BigDecimal" )

     private BigDecimal studentAgeDec;

}

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// 数据列表 List

List<Student> studentList = new ArrayList<>();

Student student = new Student();

student.setStudentId( "20220930000001" );

student.setStudentName( "赵甲" );

student.setStudentSex( "1" );

student.setStudentAgeInt( 11 );

student.setStudentAgeDou( 11.11 );

student.setStudentAgeDec( new BigDecimal( 11.11 ));

studentList.add(student);

student = new Student();

student.setStudentId( "20220930000002" );

student.setStudentName( "钱乙" );

student.setStudentSex( "2" );

student.setStudentAgeInt( 12 );

student.setStudentAgeDou( 12.12 );

student.setStudentAgeDec( new BigDecimal( 12.12 ));

studentList.add(student);

student = new Student();

student.setStudentId( "20220930000003" );

student.setStudentName( "孙丙" );

student.setStudentSex( "1" );

student.setStudentAgeInt( 13 );

student.setStudentAgeDou( 13.13 );

student.setStudentAgeDec( new BigDecimal( 13.13 ));

studentList.add(student);

student = new Student();

student.setStudentId( "20220930000004" );

student.setStudentName( "李丁" );

student.setStudentSex( "2" );

student.setStudentAgeInt( 14 );

student.setStudentAgeDou( 14.14 );

student.setStudentAgeDec( new BigDecimal( 14.14 ));

studentList.add(student);

student = new Student();

student.setStudentId( "20220930000005" );

student.setStudentName( "周戊" );

student.setStudentSex( "1" );

student.setStudentAgeInt( 15 );

student.setStudentAgeDou( 15.15 );

student.setStudentAgeDec( new BigDecimal( 15.15 ));

studentList.add(student);

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// 数据Map

Map<String,Student> studentMap = new HashMap<>( 5 );

Student student = new Student();

student.setStudentId( "20220930000001" );

student.setStudentName( "赵甲" );

student.setStudentSex( "1" );

student.setStudentAgeInt( 11 );

student.setStudentAgeDou( 11.11 );

student.setStudentAgeDec( new BigDecimal( 11.11 ));

studentMap.put(student.getStudentId(),student);

student = new Student();

student.setStudentId( "20220930000002" );

student.setStudentName( "钱乙" );

student.setStudentSex( "2" );

student.setStudentAgeInt( 12 );

student.setStudentAgeDou( 12.12 );

student.setStudentAgeDec( new BigDecimal( 12.12 ));

studentMap.put(student.getStudentId(),student);

student = new Student();

student.setStudentId( "20220930000003" );

student.setStudentName( "孙丙" );

student.setStudentSex( "1" );

student.setStudentAgeInt( 13 );

student.setStudentAgeDou( 13.13 );

student.setStudentAgeDec( new BigDecimal( 13.13 ));

studentMap.put(student.getStudentId(),student);

student = new Student();

student.setStudentId( "20220930000004" );

student.setStudentName( "李丁" );

student.setStudentSex( "2" );

student.setStudentAgeInt( 14 );

student.setStudentAgeDou( 14.14 );

student.setStudentAgeDec( new BigDecimal( 14.14 ));

studentMap.put(student.getStudentId(),student);

student = new Student();

student.setStudentId( "20220930000005" );

student.setStudentName( "周戊" );

student.setStudentSex( "1" );

student.setStudentAgeInt( 15 );

student.setStudentAgeDou( 15.15 );

student.setStudentAgeDec( new BigDecimal( 15.15 ));

studentMap.put(student.getStudentId(),student);

 2.过滤-filter

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// 过滤所有女生

List<Student> studentListT = studentList.stream()

         .filter(item -> "2" .equals(item.getStudentSex())).collect(Collectors.toList());

// 过滤12岁以上学生（3种数据类型示例）

studentListT = studentList.stream().filter(item -> item.getStudentAgeInt() > 12 ).collect(Collectors.toList());

studentListT = studentList.stream().filter(item -> item.getStudentAgeDou() > 12 ).collect(Collectors.toList());

studentListT = studentList.stream()

         .filter(item -> item.getStudentAgeDec()测试数据pareTo( new BigDecimal( 12 )) > 0 ).collect(Collectors.toList());

// 过滤12岁以上男生（2种方法示例）

studentListT = studentList.stream().filter(item -> "1" .equals(item.getStudentSex()))

         .filter(item -> item.getStudentAgeInt() > 12 ).collect(Collectors.toList());

studentListT = studentList.stream()

         .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

http://HdhCmsTesttuohang.net/article/2735.html

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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原文链接：https://blog.csdn.net/weixin_44200996/article/details/127067774

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