Builder模式实例 MyBatis的ResultMapping和ResultMap

MyBatis的ResultMapping和ResultMap

CSDN LoveLion
复杂对象的组装与创建——建造者模式（一）
Effective java 第3版中描述的Builder模式
Java设计模式14：建造者模式
2个类都使用了Builder来构建对象。

ResultMapping

package org.apache.ibatis.mapping;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Set;

import org.apache.ibatis.session.Configuration;
import org.apache.ibatis.type.JdbcType;
import org.apache.ibatis.type.TypeHandler;
import org.apache.ibatis.type.TypeHandlerRegistry;

public class ResultMapping {

  private Configuration configuration;
  private String property;
  private String column;
  private Class<?> javaType;
  private JdbcType jdbcType;
  private TypeHandler<?> typeHandler;
  private String nestedResultMapId;
  private String nestedQueryId;
  private Set<String> notNullColumns;
  private String columnPrefix;
  private List<ResultFlag> flags;
  private List<ResultMapping> composites;
  private String resultSet;
  private String foreignColumn;
  private boolean lazy;

  ResultMapping() {
  }

  public static class Builder {
    private ResultMapping resultMapping = new ResultMapping();

    public Builder(Configuration configuration, String property, String column, TypeHandler<?> typeHandler) {
      this(configuration, property);
      resultMapping.column = column;
      resultMapping.typeHandler = typeHandler;
    }

    public Builder(Configuration configuration, String property, String column, Class<?> javaType) {
      this(configuration, property);
      resultMapping.column = column;
      resultMapping.javaType = javaType;
    }

    public Builder(Configuration configuration, String property) {
      resultMapping.configuration = configuration;
      resultMapping.property = property;
      resultMapping.flags = new ArrayList<>();
      resultMapping.composites = new ArrayList<>();
      resultMapping.lazy = configuration.isLazyLoadingEnabled();
    }

    public Builder javaType(Class<?> javaType) {
      resultMapping.javaType = javaType;
      return this;
    }

    public Builder jdbcType(JdbcType jdbcType) {
      resultMapping.jdbcType = jdbcType;
      return this;
    }

    public Builder nestedResultMapId(String nestedResultMapId) {
      resultMapping.nestedResultMapId = nestedResultMapId;
      return this;
    }

    public Builder nestedQueryId(String nestedQueryId) {
      resultMapping.nestedQueryId = nestedQueryId;
      return this;
    }

    public Builder resultSet(String resultSet) {
      resultMapping.resultSet = resultSet;
      return this;
    }

    public Builder foreignColumn(String foreignColumn) {
      resultMapping.foreignColumn = foreignColumn;
      return this;
    }

    public Builder notNullColumns(Set<String> notNullColumns) {
      resultMapping.notNullColumns = notNullColumns;
      return this;
    }

    public Builder columnPrefix(String columnPrefix) {
      resultMapping.columnPrefix = columnPrefix;
      return this;
    }

    public Builder flags(List<ResultFlag> flags) {
      resultMapping.flags = flags;
      return this;
    }

    public Builder typeHandler(TypeHandler<?> typeHandler) {
      resultMapping.typeHandler = typeHandler;
      return this;
    }

    public Builder composites(List<ResultMapping> composites) {
      resultMapping.composites = composites;
      return this;
    }

    public Builder lazy(boolean lazy) {
      resultMapping.lazy = lazy;
      return this;
    }

    public ResultMapping build() {
      // lock down collections
      resultMapping.flags = Collections.unmodifiableList(resultMapping.flags);
      resultMapping.composites = Collections.unmodifiableList(resultMapping.composites);
      resolveTypeHandler();
      validate();
      return resultMapping;
    }

    private void validate() {
      // Issue #697: cannot define both nestedQueryId and nestedResultMapId
      if (resultMapping.nestedQueryId != null && resultMapping.nestedResultMapId != null) {
        throw new IllegalStateException("Cannot define both nestedQueryId and nestedResultMapId in property " + resultMapping.property);
      }
      // Issue #5: there should be no mappings without typehandler
      if (resultMapping.nestedQueryId == null && resultMapping.nestedResultMapId == null && resultMapping.typeHandler == null) {
        throw new IllegalStateException("No typehandler found for property " + resultMapping.property);
      }
      // Issue #4 and GH #39: column is optional only in nested resultmaps but not in the rest
      if (resultMapping.nestedResultMapId == null && resultMapping.column == null && resultMapping.composites.isEmpty()) {
        throw new IllegalStateException("Mapping is missing column attribute for property " + resultMapping.property);
      }
      if (resultMapping.getResultSet() != null) {
        int numColumns = 0;
        if (resultMapping.column != null) {
          numColumns = resultMapping.column.split(",").length;
        }
        int numForeignColumns = 0;
        if (resultMapping.foreignColumn != null) {
          numForeignColumns = resultMapping.foreignColumn.split(",").length;
        }
        if (numColumns != numForeignColumns) {
          throw new IllegalStateException("There should be the same number of columns and foreignColumns in property " + resultMapping.property);
        }
      }
    }

    private void resolveTypeHandler() {
      if (resultMapping.typeHandler == null && resultMapping.javaType != null) {
        Configuration configuration = resultMapping.configuration;
        TypeHandlerRegistry typeHandlerRegistry = configuration.getTypeHandlerRegistry();
        resultMapping.typeHandler = typeHandlerRegistry.getTypeHandler(resultMapping.javaType, resultMapping.jdbcType);
      }
    }

    public Builder column(String column) {
      resultMapping.column = column;
      return this;
    }
  }

  public String getProperty() {
    return property;
  }

  public String getColumn() {
    return column;
  }

  public Class<?> getJavaType() {
    return javaType;
  }

  public JdbcType getJdbcType() {
    return jdbcType;
  }

  public TypeHandler<?> getTypeHandler() {
    return typeHandler;
  }

  public String getNestedResultMapId() {
    return nestedResultMapId;
  }

  public String getNestedQueryId() {
    return nestedQueryId;
  }

  public Set<String> getNotNullColumns() {
    return notNullColumns;
  }

  public String getColumnPrefix() {
    return columnPrefix;
  }

  public List<ResultFlag> getFlags() {
    return flags;
  }

  public List<ResultMapping> getComposites() {
    return composites;
  }

  public boolean isCompositeResult() {
    return this.composites != null && !this.composites.isEmpty();
  }

  public String getResultSet() {
    return this.resultSet;
  }

  public String getForeignColumn() {
    return foreignColumn;
  }

  public void setForeignColumn(String foreignColumn) {
    this.foreignColumn = foreignColumn;
  }

  public boolean isLazy() {
    return lazy;
  }

  public void setLazy(boolean lazy) {
    this.lazy = lazy;
  }

  @Override
  public boolean equals(Object o) {
    if (this == o) {
      return true;
    }
    if (o == null || getClass() != o.getClass()) {
      return false;
    }

    ResultMapping that = (ResultMapping) o;

    return property != null && property.equals(that.property);
  }

  @Override
  public int hashCode() {
    if (property != null) {
      return property.hashCode();
    } else if (column != null) {
      return column.hashCode();
    } else {
      return 0;
    }
  }
}

ResultMap

package org.apache.ibatis.mapping;

import java.lang.annotation.Annotation;
import java.lang.reflect.Constructor;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashSet;
import java.util.List;
import java.util.Locale;
import java.util.Set;

import org.apache.ibatis.annotations.Param;
import org.apache.ibatis.builder.BuilderException;
import org.apache.ibatis.logging.Log;
import org.apache.ibatis.logging.LogFactory;
import org.apache.ibatis.reflection.ParamNameUtil;
import org.apache.ibatis.session.Configuration;

public class ResultMap {
  private Configuration configuration;

  private String id;
  private Class<?> type;
  private List<ResultMapping> resultMappings;
  private List<ResultMapping> idResultMappings;
  private List<ResultMapping> constructorResultMappings;
  private List<ResultMapping> propertyResultMappings;
  private Set<String> mappedColumns;
  private Set<String> mappedProperties;
  private Discriminator discriminator;
  private boolean hasNestedResultMaps;
  private boolean hasNestedQueries;
  private Boolean autoMapping;

  private ResultMap() {
  }

  public static class Builder {
    private static final Log log = LogFactory.getLog(Builder.class);

    private ResultMap resultMap = new ResultMap();

    public Builder(Configuration configuration, String id, Class<?> type, List<ResultMapping> resultMappings) {
      this(configuration, id, type, resultMappings, null);
    }

    public Builder(Configuration configuration, String id, Class<?> type, List<ResultMapping> resultMappings, Boolean autoMapping) {
      resultMap.configuration = configuration;
      resultMap.id = id;
      resultMap.type = type;
      resultMap.resultMappings = resultMappings;
      resultMap.autoMapping = autoMapping;
    }

    public Builder discriminator(Discriminator discriminator) {
      resultMap.discriminator = discriminator;
      return this;
    }

    public Class<?> type() {
      return resultMap.type;
    }

    public ResultMap build() {
      if (resultMap.id == null) {
        throw new IllegalArgumentException("ResultMaps must have an id");
      }
      resultMap.mappedColumns = new HashSet<>();
      resultMap.mappedProperties = new HashSet<>();
      resultMap.idResultMappings = new ArrayList<>();
      resultMap.constructorResultMappings = new ArrayList<>();
      resultMap.propertyResultMappings = new ArrayList<>();
      final List<String> constructorArgNames = new ArrayList<>();
      for (ResultMapping resultMapping : resultMap.resultMappings) {
        resultMap.hasNestedQueries = resultMap.hasNestedQueries || resultMapping.getNestedQueryId() != null;
        resultMap.hasNestedResultMaps = resultMap.hasNestedResultMaps || (resultMapping.getNestedResultMapId() != null && resultMapping.getResultSet() == null);
        final String column = resultMapping.getColumn();
        if (column != null) {
          resultMap.mappedColumns.add(column.toUpperCase(Locale.ENGLISH));
        } else if (resultMapping.isCompositeResult()) {
          for (ResultMapping compositeResultMapping : resultMapping.getComposites()) {
            final String compositeColumn = compositeResultMapping.getColumn();
            if (compositeColumn != null) {
              resultMap.mappedColumns.add(compositeColumn.toUpperCase(Locale.ENGLISH));
            }
          }
        }
        final String property = resultMapping.getProperty();
        if (property != null) {
          resultMap.mappedProperties.add(property);
        }
        if (resultMapping.getFlags().contains(ResultFlag.CONSTRUCTOR)) {
          resultMap.constructorResultMappings.add(resultMapping);
          if (resultMapping.getProperty() != null) {
            constructorArgNames.add(resultMapping.getProperty());
          }
        } else {
          resultMap.propertyResultMappings.add(resultMapping);
        }
        if (resultMapping.getFlags().contains(ResultFlag.ID)) {
          resultMap.idResultMappings.add(resultMapping);
        }
      }
      if (resultMap.idResultMappings.isEmpty()) {
        resultMap.idResultMappings.addAll(resultMap.resultMappings);
      }
      if (!constructorArgNames.isEmpty()) {
        final List<String> actualArgNames = argNamesOfMatchingConstructor(constructorArgNames);
        if (actualArgNames == null) {
          throw new BuilderException("Error in result map '" + resultMap.id
              + "'. Failed to find a constructor in '"
              + resultMap.getType().getName() + "' by arg names " + constructorArgNames
              + ". There might be more info in debug log.");
        }
        resultMap.constructorResultMappings.sort((o1, o2) -> {
          int paramIdx1 = actualArgNames.indexOf(o1.getProperty());
          int paramIdx2 = actualArgNames.indexOf(o2.getProperty());
          return paramIdx1 - paramIdx2;
        });
      }
      // lock down collections
      resultMap.resultMappings = Collections.unmodifiableList(resultMap.resultMappings);
      resultMap.idResultMappings = Collections.unmodifiableList(resultMap.idResultMappings);
      resultMap.constructorResultMappings = Collections.unmodifiableList(resultMap.constructorResultMappings);
      resultMap.propertyResultMappings = Collections.unmodifiableList(resultMap.propertyResultMappings);
      resultMap.mappedColumns = Collections.unmodifiableSet(resultMap.mappedColumns);
      return resultMap;
    }

    private List<String> argNamesOfMatchingConstructor(List<String> constructorArgNames) {
      Constructor<?>[] constructors = resultMap.type.getDeclaredConstructors();
      for (Constructor<?> constructor : constructors) {
        Class<?>[] paramTypes = constructor.getParameterTypes();
        if (constructorArgNames.size() == paramTypes.length) {
          List<String> paramNames = getArgNames(constructor);
          if (constructorArgNames.containsAll(paramNames)
              && argTypesMatch(constructorArgNames, paramTypes, paramNames)) {
            return paramNames;
          }
        }
      }
      return null;
    }

    private boolean argTypesMatch(final List<String> constructorArgNames,
        Class<?>[] paramTypes, List<String> paramNames) {
      for (int i = 0; i < constructorArgNames.size(); i++) {
        Class<?> actualType = paramTypes[paramNames.indexOf(constructorArgNames.get(i))];
        Class<?> specifiedType = resultMap.constructorResultMappings.get(i).getJavaType();
        if (!actualType.equals(specifiedType)) {
          if (log.isDebugEnabled()) {
            log.debug("While building result map '" + resultMap.id
                + "', found a constructor with arg names " + constructorArgNames
                + ", but the type of '" + constructorArgNames.get(i)
                + "' did not match. Specified: [" + specifiedType.getName() + "] Declared: ["
                + actualType.getName() + "]");
          }
          return false;
        }
      }
      return true;
    }

    private List<String> getArgNames(Constructor<?> constructor) {
      List<String> paramNames = new ArrayList<>();
      List<String> actualParamNames = null;
      final Annotation[][] paramAnnotations = constructor.getParameterAnnotations();
      int paramCount = paramAnnotations.length;
      for (int paramIndex = 0; paramIndex < paramCount; paramIndex++) {
        String name = null;
        for (Annotation annotation : paramAnnotations[paramIndex]) {
          if (annotation instanceof Param) {
            name = ((Param) annotation).value();
            break;
          }
        }
        if (name == null && resultMap.configuration.isUseActualParamName()) {
          if (actualParamNames == null) {
            actualParamNames = ParamNameUtil.getParamNames(constructor);
          }
          if (actualParamNames.size() > paramIndex) {
            name = actualParamNames.get(paramIndex);
          }
        }
        paramNames.add(name != null ? name : "arg" + paramIndex);
      }
      return paramNames;
    }
  }

  public String getId() {
    return id;
  }

  public boolean hasNestedResultMaps() {
    return hasNestedResultMaps;
  }

  public boolean hasNestedQueries() {
    return hasNestedQueries;
  }

  public Class<?> getType() {
    return type;
  }

  public List<ResultMapping> getResultMappings() {
    return resultMappings;
  }

  public List<ResultMapping> getConstructorResultMappings() {
    return constructorResultMappings;
  }

  public List<ResultMapping> getPropertyResultMappings() {
    return propertyResultMappings;
  }

  public List<ResultMapping> getIdResultMappings() {
    return idResultMappings;
  }

  public Set<String> getMappedColumns() {
    return mappedColumns;
  }

  public Set<String> getMappedProperties() {
    return mappedProperties;
  }

  public Discriminator getDiscriminator() {
    return discriminator;
  }

  public void forceNestedResultMaps() {
    hasNestedResultMaps = true;
  }

  public Boolean getAutoMapping() {
    return autoMapping;
  }

}