使用Lombok簡化你的代碼

時間 2019-12-13

標籤使用 lombok 簡化代碼欄目 Java 简体版

原文原文鏈接

1、安裝

eclipse

下載：https://projectlombok.org/
雙擊安裝便可。 html

重啓eclipse/myeclipsejava

若是有報錯，clean一下項目就ok了。apache

intellij

安裝lombok插件便可
setting→plugins→搜lombok→安裝（須要重啓） eclipse

重啓intelliJ 函數

2、Lombok用法

註解說明

val：用在局部變量前面，至關於將變量聲明爲final
@NonNull：給方法參數增長這個註解會自動在方法內對該參數進行是否爲空的校驗，若是爲空，則拋出NPE（NullPointerException）
@Cleanup：自動管理資源，用在局部變量以前，在當前變量範圍內即將執行完畢退出以前會自動清理資源，自動生成try-finally這樣的代碼來關閉流
@Getter/@Setter：用在屬性上，不再用本身手寫setter和getter方法了，還能夠指定訪問範圍
@ToString：用在類上，能夠自動覆寫toString方法，固然還能夠加其餘參數，例如@ToString(exclude=」id」)排除id屬性，或者@ToString(callSuper=true, includeFieldNames=true)調用父類的toString方法，包含全部屬性
@EqualsAndHashCode：用在類上，自動生成equals方法和hashCode方法
@NoArgsConstructor, @RequiredArgsConstructor and @AllArgsConstructor：用在類上，自動生成無參構造和使用全部參數的構造函數以及把全部@NonNull屬性做爲參數的構造函數，若是指定staticName = 「of」參數，同時還會生成一個返回類對象的靜態工廠方法，比使用構造函數方便不少
@Data：註解在類上，至關於同時使用了@ToString、@EqualsAndHashCode、@Getter、@Setter和@RequiredArgsConstrutor這些註解，對於POJO類十分有用
@Value：用在類上，是@Data的不可變形式，至關於爲屬性添加final聲明，只提供getter方法，而不提供setter方法
@Builder：用在類、構造器、方法上，爲你提供複雜的builder APIs，讓你能夠像以下方式同樣調用Person.builder().name("Adam Savage").city("San Francisco").job("Mythbusters").job("Unchained Reaction").build();更多說明參考Builder
@SneakyThrows：自動拋受檢異常，而無需顯式在方法上使用throws語句
@Synchronized：用在方法上，將方法聲明爲同步的，並自動加鎖，而鎖對象是一個私有的屬性$lock或$LOCK，而java中的synchronized關鍵字鎖對象是this，鎖在this或者本身的類對象上存在反作用，就是你不能阻止非受控代碼去鎖this或者類對象，這可能會致使競爭條件或者其它線程錯誤
@Getter(lazy=true)：能夠替代經典的Double Check Lock樣板代碼
@Log：根據不一樣的註解生成不一樣類型的log對象，可是實例名稱都是log，有六種可選實現類
- @CommonsLog Creates log = org.apache.commons.logging.LogFactory.getLog(LogExample.class);
- @Log Creates log = java.util.logging.Logger.getLogger(LogExample.class.getName());
- @Log4j Creates log = org.apache.log4j.Logger.getLogger(LogExample.class);
- @Log4j2 Creates log = org.apache.logging.log4j.LogManager.getLogger(LogExample.class);
- @Slf4j Creates log = org.slf4j.LoggerFactory.getLogger(LogExample.class);
- @XSlf4j Creates log = org.slf4j.ext.XLoggerFactory.getXLogger(LogExample.class);

3、代碼示例

val示例ui

public static void main(String[] args) {
    val sets = new HashSet<String>();
    val lists = new ArrayList<String>();
    val maps = new HashMap<String, String>();
    //=>至關於以下
    final Set<String> sets2 = new HashSet<>();
    final List<String> lists2 = new ArrayList<>();
    final Map<String, String> maps2 = new HashMap<>();
}

@NonNull示例this

    public void notNullExample(@NonNull String string) {
      string.length();
    }

    //=>至關於
     public void notNullExample(String string) {
       if (string != null) {
          string.length();
       } else {
          throw new NullPointerException("null");
       }
    }

@Cleanup示例atom

public static void main(String[] args) {
    try {
        @Cleanup InputStream inputStream = new FileInputStream(args[0]);
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    }
    //=>至關於
    InputStream inputStream = null;
    try {
        inputStream = new FileInputStream(args[0]);
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } finally {
        if (inputStream != null) {
            try {
                inputStream.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

@Getter/@Setter示例插件

@Setter(AccessLevel.PUBLIC)
@Getter(AccessLevel.PROTECTED)
private int id;
private String shap;

@ToString示例線程

@ToString(exclude = "id", callSuper = true, includeFieldNames = true)
public class LombokDemo {
    private int id;
    private String name;
    private int age;

    public static void main(String[] args) {
        //輸出LombokDemo(super=LombokDemo@48524010, name=null, age=0)
        System.out.println(new LombokDemo());
    }
}

@EqualsAndHashCode示例

@EqualsAndHashCode(exclude = {"id", "shape"}, callSuper = false)
public class LombokDemo {
    private int id;
    private String shap;
}

@NoArgsConstructor, @RequiredArgsConstructor and @AllArgsConstructor示例

@NoArgsConstructor
@RequiredArgsConstructor(staticName = "of")
@AllArgsConstructor
public class LombokDemo {
    @NonNull
    private int id;
    @NonNull
    private String shap;
    private int age;
    public static void main(String[] args) {
        new LombokDemo(1, "circle");
        //使用靜態工廠方法
        LombokDemo.of(2, "circle");
        //無參構造
        new LombokDemo();
        //包含全部參數
        new LombokDemo(1, "circle", 2);
    }
}

@Data示例

import lombok.Data;
@Data
public class Menu {
    private String shopId;
    private String skuMenuId;
    private String skuName;
    private String normalizeSkuName;
    private String dishMenuId;
    private String dishName;
    private String dishNum;
    //默認閾值
    private float thresHold = 0;
    //新閾值
    private float newThresHold = 0;
    //總得分
    private float totalScore = 0;
}

在IntelliJ中按下Ctrl+F12就能夠看到Lombok已經爲咱們自動生成了一系列的方法。

@Value示例

@Value
public class LombokDemo {
    @NonNull
    private int id;
    @NonNull
    private String shap;
    private int age;
    //至關於
    private final int id;
    public int getId() {
        return this.id;
    }
    ...
}

@Builder示例

@Builder
public class BuilderExample {
    private String name;
    private int age;
    @Singular
    private Set<String> occupations;
    public static void main(String[] args) {
        BuilderExample test = BuilderExample.builder().age(11).name("test").build();
    }
}

@SneakyThrows示例

import lombok.SneakyThrows;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.InputStream;
import java.io.UnsupportedEncodingException;
public class Test {
    @SneakyThrows()
    public void read() {
        InputStream inputStream = new FileInputStream("");
    }
    @SneakyThrows
    public void write() {
        throw new UnsupportedEncodingException();
    }
    //至關於
    public void read() throws FileNotFoundException {
        InputStream inputStream = new FileInputStream("");
    }
    public void write() throws UnsupportedEncodingException {
        throw new UnsupportedEncodingException();
    }
}

@Synchronized示例

public class SynchronizedDemo {
    @Synchronized
    public static void hello() {
        System.out.println("world");
    }
    //至關於
    private static final Object $LOCK = new Object[0];
    public static void hello() {
        synchronized ($LOCK) {
            System.out.println("world");
        }
    }
}

@Getter(lazy = true)

    public class GetterLazyExample {
      @Getter(lazy = true)
      private final double[] cached = expensive();
      private double[] expensive() {
          double[] result = new double[1000000];
          for (int i = 0; i < result.length; i++) {
            result[i] = Math.asin(i);
          }
        return result;
      }
    }

    import java.util.concurrent.atomic.AtomicReference;
    public class GetterLazyExample {
       private final AtomicReference<java.lang.Object> cached = new AtomicReference<>();
       public double[] getCached() {
          java.lang.Object value = this.cached.get();
          if (value == null) {
              synchronized (this.cached) {
                  value = this.cached.get();
                  if (value == null) {
                      final double[] actualValue = expensive();
                      value = actualValue == null ? this.cached : actualValue;
                      this.cached.set(value);
                  }
              }
          }
          return (double[]) (value == this.cached ? null : value);
       }
       private double[] expensive() {
          double[] result = new double[1000000];
          for (int i = 0; i < result.length; i++) {
              result[i] = Math.asin(i);
          }
          return result;
       }
    }