lombok guide
lombok是什么
lombok是一款用于减少重复代码（或模板类代码）的开源框架。
相信大家都用过jdbc操作数据库，过程很麻烦，而且千篇一律……
同理，项目中最常见的代码set/get、toString、equals、hashCode、Logger……
lombok怎么用
这里不谈原理，不讲性能，只谈使用。
这里只说比较常用的，其他偏门的查API
lombok内置很多注解，这些注解可以帮我们减少重复代码
@Getter、@Setter
@Getter @Setter private boolean employed = true;
@Setter(AccessLevel.PROTECTED) private String name;
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private boolean employed = true;
private String name;
public boolean isEmployed() {
return employed;
}
public void setEmployed(final boolean employed) {
this.employed = employed;
}
protected void setName(final String name) {
this.name = name;
}
分隔线上是lombok注解的使用例子，分割线下是lombok为我们生成的或者我们以前就是那么干的
@NonNull
public class Family{
@Getter @Setter @NonNull
private List<Person> members;
}
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@NonNull
private List<Person> members;
public Family(@NonNull final List<Person> members) {
if (members == null) throw new java.lang.NullPointerException("members");
this.members = members;
}
@NonNull
public List<Person> getMembers() {
return members;
}
public void setMembers(@NonNull final List<Person> members) {
if (members == null) throw new java.lang.NullPointerException("members");
this.members = members;
}
非null校验
@ToString
@ToString(callSuper=true,exclude="someExcludedField")
public class Foo extends Bar {
private boolean someBoolean = true;
private String someStringField;
private float someExcludedField;
}
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public class Foo extends Bar {
private boolean someBoolean = true;
private String someStringField;
private float someExcludedField;
@java.lang.Override
public java.lang.String toString() {
return "Foo(super=" + super.toString() +
", someBoolean=" + someBoolean +
", someStringField=" + someStringField + ")";
}
}
toString，可以排除某个字段，其他的可以看API
@EqualsAndHashCode
@EqualsAndHashCode(callSuper=true,exclude={"address","city","state","zip"})
public class Person extends SentientBeing {
enum Gender { Male, Female }
@NonNull private String name;
@NonNull private Gender gender;
private String ssn;
private String address;
private String city;
private String state;
private String zip;
}
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public class Person extends SentientBeing {
enum Gender {
/*public static final*/ Male /* = new Gender() */,
/*public static final*/ Female /* = new Gender() */;
}
@NonNull
private String name;
@NonNull
private Gender gender;
private String ssn;
private String address;
private String city;
private String state;
private String zip;
@java.lang.Override
public boolean equals(final java.lang.Object o) {
if (o == this) return true;
if (o == null) return false;
if (o.getClass() != this.getClass()) return false;
if (!super.equals(o)) return false;
final Person other = (Person)o;
if (this.name == null ? other.name != null : !this.name.equals(other.name)) return false;
if (this.gender == null ? other.gender != null : !this.gender.equals(other.gender)) return false;
if (this.ssn == null ? other.ssn != null : !this.ssn.equals(other.ssn)) return false;
return true;
}
@java.lang.Override
public int hashCode() {
final int PRIME = 31;
int result = 1;
result = result * PRIME + super.hashCode();
result = result * PRIME + (this.name == null ? 0 : this.name.hashCode());
result = result * PRIME + (this.gender == null ? 0 : this.gender.hashCode());
result = result * PRIME + (this.ssn == null ? 0 : this.ssn.hashCode());
return result;
}
}
同样可以exclude特定字段
@Data
@Data是lombok的工具集，包含了@ToString、@EqualsAndHashCode、@Getter和@Setter
@Data(staticConstructor="of")
public class Company {
private final Person founder;
private String name;
private List<Person> employees;
}
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public class Company {
private final Person founder;
private String name;
private List<Person> employees;
private Company(final Person founder) {
this.founder = founder;
}
public static Company of(final Person founder) {
return new Company(founder);
}
public Person getFounder() {
return founder;
}
public String getName() {
return name;
}
public void setName(final String name) {
this.name = name;
}
public List<Person> getEmployees() {
return employees;
}
public void setEmployees(final List<Person> employees) {
this.employees = employees;
}
@java.lang.Override
public boolean equals(final java.lang.Object o) {
if (o == this) return true;
if (o == null) return false;
if (o.getClass() != this.getClass()) return false;
final Company other = (Company)o;
if (this.founder == null ? other.founder != null : !this.founder.equals(other.founder)) return false;
if (this.name == null ? other.name != null : !this.name.equals(other.name)) return false;
if (this.employees == null ? other.employees != null : !this.employees.equals(other.employees)) return false;
return true;
}
@java.lang.Override
public int hashCode() {
final int PRIME = 31;
int result = 1;
result = result * PRIME + (this.founder == null ? 0 : this.founder.hashCode());
result = result * PRIME + (this.name == null ? 0 : this.name.hashCode());
result = result * PRIME + (this.employees == null ? 0 : this.employees.hashCode());
return result;
}
@java.lang.Override
public java.lang.String toString() {
return "Company(founder=" + founder + ", name=" + name + ", employees=" + employees + ")";
}
}
@NoArgsConstructor、@AllArgsConstructor
无参构造和全参构造
@Builder
@Builder
class Example {
private int foo;
private final String bar;
}
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class Example<T> {
private T foo;
private final String bar;
private Example(T foo, String bar) {
this.foo = foo;
this.bar = bar;
}
public static <T> ExampleBuilder<T> builder() {
return new ExampleBuilder<T>();
}
public static class ExampleBuilder<T> {
private T foo;
private String bar;
private ExampleBuilder() {}
public ExampleBuilder foo(T foo) {
this.foo = foo;
return this;
}
public ExampleBuilder bar(String bar) {
this.bar = bar;
return this;
}
@java.lang.Override public String toString() {
return "ExampleBuilder(foo = " + foo + ", bar = " + bar + ")";
}
public Example build() {
return new Example(foo, bar);
}
}
}
builder模式需要注意一点，因为builder生成的构造是private的，会引起一些框架的反射装配问题，所以一般与@ NoArgsConstructor一起使用
各种日志
包括apache、jdk logging、jboss log、log4j、slf4j。这里只讲@Slf4j
@Slf4j
public class LogExample {
}
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public class LogExample {
private static final org.slf4j.Logger log = org.slf4j.LoggerFactory.getLogger(LogExample.class);
}
利与弊
使用任何框架都有两面性
利：
1.减少重复代码
2.减少维护成本、增强可读性、减少基础性bug
弊：
1.降低性能
2.其他
