Java中一个只实现了接口的类，在它的构造方法中调用了super()方法，这样做有什么意义呢

Question

今天在看spring源码spring-core包中的EncodedResource.java时发现它的其中一个构造方法里出现了：
private EncodedResource(Resource resource, String encoding, Charset charset) {
super();
Assert.notNull(resource, "Resource must not be null");
this.resource = resource;
this.encoding = encoding;
this.charset = charset;
}
一开始并不知道super()到底做了什么，后来经别人提醒知道了原来这是在调用Object类的
的构造方法，这样是对的吗？还有，这样做有什么意义吗？

Answer 1

此处附上源代码：
EncodedResource.java
/*

• Copyright 2002-2016 the original author or authors. *
• Licensed under the Apache License, Version 2.0 (the "License");
• you may not use this file except in compliance with the License.
• You may obtain a copy of the License at *
• http://www.apache.org/licenses/LICENSE-2.0 *
• Unless required by applicable law or agreed to in writing, software
• distributed under the License is distributed on an "AS IS" BASIS,
• WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
• See the License for the specific language governing permissions and
• limitations under the License. */

package org.springframework.core.io.support;

import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.Reader;
import java.nio.charset.Charset;

import org.springframework.core.io.InputStreamSource;
import org.springframework.core.io.Resource;
import org.springframework.util.Assert;
import org.springframework.util.ObjectUtils;

/**

• Holder that combines a {@link Resource} descriptor with a specific encoding
• or {@code Charset} to be used for reading from the resource. *

• Used as an argument for operations that support reading content with

• a specific encoding, typically via a {@code java.io.Reader}. *
• @author Juergen Hoeller
• @author Sam Brannen
• @since 1.2.6
• @see java.io.Reader

• @see java.nio.charset.Charset
  */
  public class EncodedResource implements InputStreamSource {

  private final Resource resource;

  private final String encoding;

  private final Charset charset;

  /**

  • Create a new {@code EncodedResource} for the given {@code Resource},
  • not specifying an explicit encoding or {@code Charset}.
  • @param resource the {@code Resource} to hold (never {@code null}) */ public EncodedResource(Resource resource) { this(resource, null, null); }

  /**

  • Create a new {@code EncodedResource} for the given {@code Resource},
  • using the specified {@code encoding}.
  • @param resource the {@code Resource} to hold (never {@code null})
  • @param encoding the encoding to use for reading from the resource */ public EncodedResource(Resource resource, String encoding) { this(resource, encoding, null); }

  /**

  • Create a new {@code EncodedResource} for the given {@code Resource},
  • using the specified {@code Charset}.
  • @param resource the {@code Resource} to hold (never {@code null})
  • @param charset the {@code Charset} to use for reading from the resource */ public EncodedResource(Resource resource, Charset charset) { this(resource, null, charset); }

  private EncodedResource(Resource resource, String encoding, Charset charset) {
  super();
  Assert.notNull(resource, "Resource must not be null");
  this.resource = resource;
  this.encoding = encoding;
  this.charset = charset;
  }

  /**

  • Return the {@code Resource} held by this {@code EncodedResource}. */ public final Resource getResource() { return this.resource; }

  /**

  • Return the encoding to use for reading from the {@linkplain #getResource() resource},
  • or {@code null} if none specified. */ public final String getEncoding() { return this.encoding; }

  /**

  • Return the {@code Charset} to use for reading from the {@linkplain #getResource() resource},
  • or {@code null} if none specified. */ public final Charset getCharset() { return this.charset; }

  /**

  • Determine whether a {@link Reader} is required as opposed to an {@link InputStream},
  • i.e. whether an {@linkplain #getEncoding() encoding} or a {@link #getCharset() Charset}
  • has been specified.
  • @see #getReader()
  • @see #getInputStream() */ public boolean requiresReader() { return (this.encoding != null || this.charset != null); }

  /**

  • Open a {@code java.io.Reader} for the specified resource, using the specified
  • {@link #getCharset() Charset} or {@linkplain #getEncoding() encoding}
  • (if any).
  • @throws IOException if opening the Reader failed
  • @see #requiresReader()
  • @see #getInputStream() */ public Reader getReader() throws IOException { if (this.charset != null) { return new InputStreamReader(this.resource.getInputStream(), this.charset); } else if (this.encoding != null) { return new InputStreamReader(this.resource.getInputStream(), this.encoding); } else { return new InputStreamReader(this.resource.getInputStream()); } }

  /**

  • Open a {@code java.io.InputStream} for the specified resource, ignoring any
  • specified {@link #getCharset() Charset} or {@linkplain #getEncoding() encoding}.
  • @throws IOException if opening the InputStream failed
  • @see #requiresReader()
  • @see #getReader() */ @Override public InputStream getInputStream() throws IOException { return this.resource.getInputStream(); }

  @Override
  public boolean equals(Object other) {
  if (this == other) {
  return true;
  }
  if (!(other instanceof EncodedResource)) {
  return false;
  }
  EncodedResource otherResource = (EncodedResource) other;
  return (this.resource.equals(otherResource.resource) &&
  ObjectUtils.nullSafeEquals(this.charset, otherResource.charset) &&
  ObjectUtils.nullSafeEquals(this.encoding, otherResource.encoding));
  }

  @Override
  public int hashCode() {
  return this.resource.hashCode();
  }

  @Override
  public String toString() {
  return this.resource.toString();
  }

}

InputStreamSource.java
/*

• Copyright 2002-2012 the original author or authors. *
• Licensed under the Apache License, Version 2.0 (the "License");
• you may not use this file except in compliance with the License.
• You may obtain a copy of the License at *
• http://www.apache.org/licenses/LICENSE-2.0 *
• Unless required by applicable law or agreed to in writing, software
• distributed under the License is distributed on an "AS IS" BASIS,
• WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
• See the License for the specific language governing permissions and
• limitations under the License. */

package org.springframework.core.io;

import java.io.IOException;
import java.io.InputStream;

/**

• Simple interface for objects that are sources for an {@link InputStream}. *

• This is the base interface for Spring's more extensive {@link Resource} interface. *

• For single-use streams, {@link InputStreamResource} can be used for any

• given {@code InputStream}. Spring's {@link ByteArrayResource} or any
• file-based {@code Resource} implementation can be used as a concrete
• instance, allowing one to read the underlying content stream multiple times.
• This makes this interface useful as an abstract content source for mail
• attachments, for example. *
• @author Juergen Hoeller
• @since 20.01.2004
• @see java.io.InputStream
• @see Resource
• @see InputStreamResource

• @see ByteArrayResource
  */
  public interface InputStreamSource {

  /**

  • Return an {@link InputStream}.

  • It is expected that each call creates a fresh stream.

  • This requirement is particularly important when you consider an API such

  • as JavaMail, which needs to be able to read the stream multiple times when
  • creating mail attachments. For such a use case, it is required
  • that each {@code getInputStream()} call returns a fresh stream.
  • @return the input stream for the underlying resource (must not be {@code null})
  • @throws IOException if the stream could not be opened
  • @see org.springframework.mail.javamail.MimeMessageHelper#addAttachment(String, InputStreamSource) */ InputStream getInputStream() throws IOException;

}