devtools-beans-streaming包是devtools系列的工具包之一，它是一个对对象列表（或称为结果集）进行查询或聚合等操作的解决方案, 提供了类似于C#中的LINQ功能
安装：
<dependency>
<groupId>com.github.paganini2008</groupId>
<artifactId>devtools-beans-streaming</artifactId>
<version>2.0.3</version>
</dependency>
兼容性：
jdk1.8+
如何使用？
devtools-beans-streaming操作的对象通常是一个List
举例说明：
比如有这样一个对象：
@Getter
@Setter
@ToString
public class Product {
private int id;
private String name;
private String location;
private Date created;
private Date expired;
private Float price;
private BigInteger sales;
private boolean export;
private Long number;
private BigDecimal freight;
private Style style;
private Salesman salesman;
public static enum Style {
HARD, SOFT;
}
@Getter
@Setter
@ToString
public static class Salesman {
private String name;
private String password;
public Salesman(String name, String password) {
this.name = name;
this.password = password;
}
}
}
然后定义一个List, 生成一批对象，随机赋值
比如：
// 定义一个List
private static final List<Product> products = new ArrayList<Product>();
static {
String[] users = new String[] { "Petter", "Jack", "Tony" };
String[] locations = new String[] { "London", "NewYork", "Tokyo", "HongKong", "Paris" };
for (int i = 0; i < 10000; i++) {
Product product = new Product();
product.setCreated(DateUtils.valueOf(2020, RandomUtils.randomInt(1, 12), RandomUtils.randomInt(1, 28)));
product.setExpired(DateUtils.addDays(product.getCreated(), 90));
product.setExport(RandomUtils.randomBoolean());
product.setFreight(BigDecimal.valueOf(RandomUtils.randomFloat(10, 100)).setScale(2, RoundingMode.HALF_UP));
product.setId(i + 1);
product.setLocation(RandomUtils.randomChoice(locations));
product.setName("Product-" + product.getId());
product.setNumber(RandomUtils.randomLong(1, 1000));
product.setPrice(RandomUtils.randomFloat(10, 1000, 2));
product.setSales(BigInteger.valueOf(RandomUtils.randomLong(10000, 100000)));
product.setStyle(Style.values()[RandomUtils.randomInt(0, 2)]);
product.setSalesman(new Product.Salesman(RandomUtils.randomChoice(users), "123456"));
products.add(product);
}
}
示例1
Predicate<Product> predicate = Restrictions.eq("location", "London");
Selector.from(products).filter(predicate).list().forEach(product -> {
System.out.println(product);
});
// Equivalent to: select * from Product where location='London'
示例2
Predicate<Product> predicate = Restrictions.lte("created", new Date());
predicate = predicate.and(Restrictions.eq("salesman.name", "Petter"));
Selector.from(products).filter(predicate).list().forEach(product -> {
System.out.println(product);
});
// select * from Product where created<= now() and salesman.name='Petter'
示例3
Selector.from(products).groupBy("location", String.class).setTransformer(new View<Product>() {
protected void setAttributes(Tuple tuple, Group<Product> group) {
tuple.set("maxPrice", group.max("price", Float.class));
tuple.set("minPrice", group.min("price", Float.class));
tuple.set("avgFreight", group.avg("freight"));
tuple.set("sumSales", group.sum("sales"));
}
}).list().forEach(tuple -> {
System.out.println(tuple);
});
// Equivalent to: select location,max(price) as maxPrice, min(price) as minPrice,avg(freight) as avgFreight,sum(sales) as sumSales from Product group by location
示例4
Selector.from(products).groupBy("location", String.class).groupBy("style", Product.Style.class).having(group -> {
return group.avg("freight").compareTo(BigDecimal.valueOf(55)) > 0;
}).setTransformer(new View<Product>() {
protected void setAttributes(Tuple tuple, Group<Product> group) {
tuple.set("maxPrice", group.max("price", Float.class));
tuple.set("minPrice", group.min("price", Float.class));
tuple.set("avgFreight", group.avg("freight"));
tuple.set("sumSales", group.sum("sales"));
}
}).list().forEach(tuple -> {
System.out.println(tuple);
});
// Equivalent to: select location,style,max(price) as maxPrice, min(price) as minPrice,avg(freight) as avgFreight,sum(sales) as sumSales from Product group by location,style having avg(freight) > 55
示例5:
Sorter<Product> sorter = Orders.descending("price", BigDecimal.class);
Selector.from(products).orderBy(sorter).list(100).forEach(product -> {
System.out.println("Name: " + product.getName() + ", Price: " + product.getPrice() + ", Freight: " + product.getFreight());
});
// Equivalent to: select name,price from Product order by price desc limit 100
