Google Guava集合在实体类中的应用示例

将实体list，转换成map，拿到所有id的集合方法。减少访问数据库。

 

实体基类BaseEntity

package com.mytest;import org.apache.commons.lang3.builder.ToStringBuilder;import org.apache.commons.lang3.builder.ToStringStyle;public class BaseEntity {private Long id;public Long getId() {return id;}public void setId(Long id) {this.id = id;}/** * 覆盖toString方法，目的显示所有JavaBean的属性值，省略写很多的getXxx的方法 */public String toString() {return ToStringBuilder.reflectionToString(this,ToStringStyle.MULTI_LINE_STYLE);}}

实体类Person

package com.mytest;public class Person extends BaseEntity{private String name;private String gender;private int age;private double weight;public Person(Long id, String name, String gender, int age, double weight) {super();this.setId(id);this.name = name;this.gender = gender;this.age = age;this.weight = weight;}public String getName() {return name;}public void setName(String name) {this.name = name;}public String getGender() {return gender;}public void setGender(String gender) {this.gender = gender;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}public double getWeight() {return weight;}public void setWeight(double weight) {this.weight = weight;}}

Example

package com.mytest;import java.util.List;import java.util.Map;import java.util.Set;import org.slf4j.Logger;import org.slf4j.LoggerFactory;import com.google.common.base.Function;import com.google.common.collect.Lists;import com.google.common.collect.Maps;import com.google.common.collect.Ordering;public class Example {    public static Logger logger = LoggerFactory.getLogger(Example.class);       public static void main(String[] args) {        List<Person> list = Lists.newArrayList();        list.add(new Person(4L,"jason", "male", 16, 120.50));        list.add(new Person(1L,"tom", "male", 48, 163.50));        list.add(new Person(3L,"john", "male", 33, 105));        list.add(new Person(2L,"rose", "female", 26, 90));                        logger.debug(list.toString());        //获取ids        List<Long> ids  = entityIds(list);  //entityIds方法        logger.debug("---------------ids-------------------");        logger.debug(ids.toString());                logger.debug("---------------maps-------------------");        //获取map        Map<Long, Person> maps = entityMaps(list); //entityMaps方法        Set<Long> keys = maps.keySet();        for (Long id : keys) {logger.debug("key: " + id + " value: " + maps.get(id));}}/** * 获取表记录集合的Id集合 * @param list * @return */public static<T extends BaseEntity> List<Long> entityIds(List<T> list){List<Long> ids = Lists.transform(list, new Function<T, Long>(){            public Long apply(T entity){        return entity.getId();            }                }); return ids;}/** * 根据实体记录，输出Map<Long id,K extend BaseEntity>集合 * @param list * @return */public static<V extends BaseEntity> Map<Long,V> entityMaps(List<V> list){        Map<Long,V> maps = Maps.uniqueIndex(list.iterator(),  new Function<V, Long>() {    @Override    public Long apply(V entity) {        return entity.getId();    }});return maps;}}

 

entityIds方法

        /** * 获取表记录集合的Id集合 * @param list * @return */public static<T extends BaseEntity> List<Long> entityIds(List<T> list){List<Long> ids = Lists.transform(list, new Function<T, Long>(){            public Long apply(T entity){        return entity.getId();            }                }); return ids;}

 

entityMaps方法

        /** * 根据实体记录，输出Map<Long id,K extend BaseEntity>集合 * @param list * @return */public static<V extends BaseEntity> Map<Long,V> entityMaps(List<V> list){        Map<Long,V> maps = Maps.uniqueIndex(list.iterator(),  new Function<V, Long>() {    @Override    public Long apply(V entity) {        return entity.getId();    }});return maps;}

 

引入包，可参考pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"><modelVersion>4.0.0</modelVersion><groupId>com.gzdfbz</groupId><artifactId>mytest</artifactId><version>0.0.1-SNAPSHOT</version><dependencies><dependency><groupId>com.google.guava</groupId><artifactId>guava</artifactId><version>18.0</version></dependency><dependency><groupId>org.apache.commons</groupId><artifactId>commons-lang3</artifactId><version>3.3.2</version></dependency><dependency><groupId>org.slf4j</groupId><artifactId>slf4j-api</artifactId><version>1.7.7</version></dependency><dependency><groupId>org.slf4j</groupId><artifactId>slf4j-log4j12</artifactId><version>1.7.7</version></dependency><dependency><groupId>joda-time</groupId><artifactId>joda-time</artifactId><version>2.3</version></dependency></dependencies></project>

log4j参考：

#log4j.rootLogger=DEBUG,consolelog4j.additivity.org.apache=true#log4j.appender.console=org.apache.log4j.ConsoleAppenderlog4j.appender.console.Threshold=DEBUGlog4j.appender.console.ImmediateFlush=truelog4j.appender.console.Target=System.errlog4j.appender.console.layout=org.apache.log4j.PatternLayout#log4j.appender.console.layout.ConversionPattern=[%-5p] %d(%r) --> [%t] %l: %m %x %nlog4j.appender.console.layout.ConversionPattern=%l: %m %x %nlog4j.appender.com.mytest =  debug

 来自：http://my.oschina.net/u/221951/blog/333286