Java开发中常用记录_Java教程

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：

TransactionStatus transactionStatus =  platformTransactionManager.getTransaction(transactionDefinition);
if (!transactionStatus.isCompleted()) {
    platformTransactionManager.commit(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：

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

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;
}

// 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);

// 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

// 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().compareTo(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());