自定义注解实战：自定义 orm 工具。生成 sql 语句 ok ~

Signed-off-by: pythonCat <pythoncat@qq.com>

Author: pythoncat1024

src/main/java/com/intellij/cat/orm/BindField.java

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+package com.intellij.cat.orm;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+/**
+ * 对表字段的注解
+ */
+@Target(ElementType.FIELD)
+@Retention(RetentionPolicy.RUNTIME)
+public @interface BindField {
+
+    // `_uid` int(32) NOT NULL AUTO_INCREMENT,
+
+    String columnName() default "";
+
+    /**
+     * 字段类型：varchar , int(25)
+     *
+     * @return field type
+     */
+    String type();
+
+    boolean notNull() default false;
+
+    boolean primaryKey() default false;
+
+    boolean unique() default false;
+
+    boolean autoIncrement() default false;
+}

src/main/java/com/intellij/cat/orm/BindTable.java

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+package com.intellij.cat.orm;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+@Target(value = ElementType.TYPE)
+@Retention(value = RetentionPolicy.RUNTIME)
+public @interface BindTable {
+
+    /**
+     * table name
+     *
+     * @return table name
+     */
+    String value();
+
+    String charset() default "utf8";
+}

src/main/java/com/intellij/cat/orm/TbUserParser.java

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+package com.intellij.cat.orm;
+
+import javax.annotation.Nullable;
+import java.lang.reflect.Field;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Locale;
+import java.util.Objects;
+
+/**
+ * 自定义注解解析类
+ */
+public class TbUserParser {
+
+    private TbUserParser() {
+    }
+
+    private static TableInfo parseClass() {
+
+        BindTable annotation = (BindTable) ((Class) User.class).getAnnotation(BindTable.class);
+//        System.out.println(annotation);
+        String charset = annotation.charset();
+        String tbName = annotation.value();
+        return new TableInfo(charset, tbName);
+
+    }
+
+
+    private static List<FieldInfo> parserField() {
+
+        Field[] fields = User.class.getDeclaredFields();
+        ArrayList<FieldInfo> infoSet = new ArrayList<>();
+
+        for (Field f : fields) {
+
+            // 没有添加该注解的字段就会返回 null
+            @Nullable
+            BindField bindF = f.getAnnotation(BindField.class);
+
+            // System.out.println("bindF==" + bindF);
+            if (Objects.nonNull(bindF)) {
+                String columnName = bindF.columnName();
+                String type = bindF.type();
+                boolean unique = bindF.unique();
+                boolean autoIncrement = bindF.autoIncrement();
+                boolean notNull = bindF.notNull();
+                boolean primaryKey = bindF.primaryKey();
+                FieldInfo info = new FieldInfo(columnName, type, notNull,
+                        autoIncrement, unique, primaryKey);
+                infoSet.add(info);
+            }
+        }
+        return infoSet;
+    }
+
+
+    public static String createTable() {
+        TableInfo tableInfo = parseClass();
+        List<FieldInfo> fieldInfoSet = parserField();
+        String head = String.format(Locale.getDefault(),
+                "CREATE TABLE IF NOT EXISTS %s(", tableInfo.tbName);
+        StringBuilder item = new StringBuilder();
+        for (FieldInfo fi : fieldInfoSet) {
+            // `chat_id` INT UNSIGNED AUTO_INCREMENT,
+            item.append(String.format(Locale.getDefault(), "`%s` ", fi.columnName))
+                    .append(String.format(Locale.getDefault(), "%s ", fi.type))
+                    .append(fi.primaryKey ? "PRIMARY KEY " : "")
+                    .append(fi.notNull ? "NOT NULL " : "")
+                    .append(fi.unique ? "UNIQUE " : "")
+                    .append(fi.autoIncrement ? "AUTO_INCREMENT," : ",");
+        }
+        if (item.charAt(item.length() - 1) == ',') {
+            item.deleteCharAt(item.length() - 1);
+        }
+        String tail = String.format(Locale.getDefault(), ") CHARSET=%s;", tableInfo.charset);
+        return head + item + tail;
+    }
+
+
+    static class TableInfo {
+        String charset;
+        String tbName;
+
+        TableInfo(String charset, String tbName) {
+            this.charset = charset;
+            this.tbName = tbName;
+        }
+    }
+
+    static class FieldInfo {
+        String columnName;
+        String type;
+        boolean notNull;
+        boolean autoIncrement;
+        boolean unique;
+        boolean primaryKey;
+
+        FieldInfo(String columnName, String type, boolean notNull,
+                  boolean autoIncrement, boolean unique, boolean primaryKey) {
+            this.columnName = columnName;
+            this.type = type;
+            this.notNull = notNull;
+            this.autoIncrement = autoIncrement;
+            this.unique = unique;
+            this.primaryKey = primaryKey;
+        }
+    }
+}

src/main/java/com/intellij/cat/orm/User.java

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+package com.intellij.cat.orm;
+
+/**
+ * 对应到 数据库中的一条记录
+ */
+@BindTable(value = "tb_user")
+public class User {
+
+    public static final int GENDER_SECRET = 0;
+    public static final int GENDER_MAIL = 1;
+    public static final int GENDER_FEMAIL = 2;
+
+    @BindField(type = "varchar(50)", notNull = true, columnName = "_name")
+    private String name;
+    @BindField(type = "int(3)", columnName = "_age")
+    private int age;
+    @BindField(type = "int(1)", notNull = true, columnName = "_gender")
+    private int gender;
+
+    @BindField(type = "int(1)", primaryKey = true, columnName = "_uid")
+    private long uid;
+
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public int getAge() {
+        return age;
+    }
+
+    public void setAge(int age) {
+        this.age = age;
+    }
+
+    public int getGender() {
+        return gender;
+    }
+
+    public void setGender(int gender) {
+        this.gender = gender;
+    }
+
+    public long getUid() {
+        return uid;
+    }
+
+    public void setUid(long uid) {
+        this.uid = uid;
+    }
+}

src/main/java/com/intellij/cat/orm/package-info.java

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+/**
+ * 注解实践
+ * 通过自定义注解，使用注解，解析注解三部曲完成一个简单的 orm 功能
+ */
+package com.intellij.cat.orm;

src/test/java/TestTableParse.java

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+import com.intellij.cat.orm.TbUserParser;
+import org.junit.Test;
+
+public class TestTableParse {
+
+
+    @Test
+    public void testParse() {
+
+        String table = TbUserParser.createTable();
+
+        System.out.println("table==\n" + table);
+    }
+}