今天写根过滤的时候一下子有点愣眼，先是想到用 java 原生的 map 循环查出来，但是觉得太 low， 后面思考了一下可以用 java8 的 lambda，写完了，又发现 google guava 有现成的方法，这里一一列出来，供参考使用。
首先提示，如果照搬我的代码的话别忘了引这些依赖
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<dependencies>
<dependency>
<groupid>junit</groupid>
<artifactid>junit</artifactid>
<version>4.12</version>
<scope>test</scope>
<exclusions>
<exclusion>
<groupid>org.hamcrest</groupid>
<artifactid>hamcrest-core</artifactid>
</exclusion>
</exclusions>
</dependency>
<dependency>
<groupid>org.hamcrest</groupid>
<artifactid>hamcrest-library</artifactid>
<version>1.3</version>
<scope>test</scope>
</dependency>
<dependency>
<groupid>com.google.guava</groupid>
<artifactid>guava</artifactid>
<version>25.1-jre</version>
</dependency>
</dependencies>
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filter by key
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public class filtermapbykeytest {
private map<integer, string> week = new hashmap<>();
@before
public void setup () {
week.put(1, "monday");
week.put(2, "tuesday");
week.put(3, "wednesday");
week.put(4, "thursday");
week.put(5, "friday");
week.put(6, "saturday");
week.put(7, "sunday");
}
/**
* java 8之前的版本
*/
@test
public void filtermapbykey () {
map<integer, string> map = new hashmap<>();
for (map.entry<integer, string> entry : week.entryset()) {
if (entry.getkey() <= 3) {
map.put(entry.getkey(), entry.getvalue());
}
}
assertthat(map.keyset(), contains(1, 2, 3));
}
/**
* java 8 lambda
*/
@test
public void filtermapbykeyjava8lambda () {
map<integer, string> map = week.entryset().stream().filter(r -> r.getkey() <= 3)
.collect(collectors.tomap(map.entry::getkey, map.entry::getvalue));
assertthat(map.keyset(), contains(1, 2, 3));
}
/**
* google guava
*/
@test
public void filtermapbykeyguava () {
map<integer, string> map = maps.filterkeys(week, r -> r <= 3);
assertthat(map.keyset(), contains(1, 2, 3));
}
}
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filter by value
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public class filtermapbyvaluetest {
private map<integer, string> week = new hashmap<>();
@before
public void setup () {
week.put(1, "monday");
week.put(2, "tuesday");
week.put(3, "wednesday");
week.put(4, "thursday");
week.put(5, "friday");
week.put(6, "saturday");
week.put(7, "sunday");
}
/**
* java 8之前的版本
*/
@test
public void filtermapbyvalue () {
map<integer, string> map = new hashmap<>();
for (map.entry<integer, string> entry : week.entryset()) {
if (entry.getvalue().startswith("s")) {
map.put(entry.getkey(), entry.getvalue());
}
}
assertthat(map.values(), contains("saturday","sunday"));
}
/**
* java 8 lambda
*/
@test
public void filtermapbyvaluejava8lambda () {
map<integer, string> map = week.entryset().stream().filter(r -> r.getvalue().startswith("s"))
.collect(collectors.tomap(map.entry::getkey, map.entry::getvalue));
assertthat(map.values(), contains("saturday","sunday"));
}
/**
* google guava
*/
@test
public void filtermapbyvalueguava () {
map<integer, string> map = maps.filtervalues(week, r -> r.startswith("s"));
assertthat(map.values(), contains("saturday","sunday"));
}
}
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总结
以上所述是小编给大家介绍的java map 通过 key 或者 value 过滤的实例代码，希望对大家有所帮助，如果大家有任何疑问请给我留言，小编会及时回复大家的。在此也非常感谢大家对服务器之家网站的支持！
原文链接：https://segmentfault.com/a/1190000015421902