取list中所有对象的某个字段先绝对值后的最大值得对象
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| Optional<QuestionnaireResult> userOp = list.stream().map((x) -> {
x.setScore(Math.abs(x.getScore()));
return x;
}).max(Comparator.comparingDouble(QuestionnaireResult::getScore));
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过滤对象集合中对象字段满足条件的对象集合
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| List<OctoSupplierProductMapping> ospm = octoSupplierProductMappings.stream().filter(o -> o.getUsed() == 0).collect(Collectors.toList());
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List中的最大值对象
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| Optional<Employee > userOp= userList.stream().max(Comparator.comparingInt(Employee ::getAge));
Employee maxEmp = userOp.get();
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或者
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| Optional<Employee > userOp= userList.stream().filter(Objects::nonNull).filter(item -> item.getAge() != null)
.sorted(Comparator.comparing(Employee::getAge).reversed()).findFirst().get();
Employee maxEmp = userOp.get();
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避免空指针,添加一个filter,判断age不能为空,
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| filter(item -> item.getAge() != null)
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或者使用orElse防止空指针。
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| Optional<Employee > userOp= employees.stream().filter(Objects::nonNull).max(Comparator.comparingInt(Employee ::getAge));
Employee maxEmp = userOp.orElse(new Employee());
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按照多字段分组
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| Map<String, List<AgentStorageReports>> stringListMap = agentStorageReportsList.stream().collect(Collectors.groupingBy(o -> o.getInitiatorTanantId() + "_" + o.getInitiatorJobNum()));
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Java从list对象集合中获取某一列的集合数据
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| List<Book> list = Lists.newArrayList();
list.add(new Book("1", "sql基础大全", 200));
list.add(new Book("2", "Java基础", 500));
System.out.println(list);
List<String> nameList = list.stream().map(Book -> Book.getName()).collect(Collectors.toList());
System.out.println(nameList);
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